NCV78703 Multiphase Booster LED Driver for Automotive Front Lighting

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Multiphase Booster LED Driver for Automotive Front Lighting

The NCV78703 is a single−chip and high efficient booster for smart Power ballast and LED Driver designed for automotive front lighting applications like high beam, low beam, DRL (daytime running light), turn indicator, fog light, static cornering, etc. The NCV78703 is in particular designed for high current LEDs and with NCV78723 (dual channel buck)/713 (single channel) provides a complete solution to drive multiple LED strings of up−to 60 V. It includes a current−mode voltage boost controller which also acts as an input filter with a minimum of external components. The available output voltage can be customized. Two devices NCV78703 can be combined and the booster circuits can operate together to function as a multiphase booster (2−phase, 3−phase, 4−phase, 5−phase, 6−phase) in order to further optimize the filtering effect of the booster and lower the total application BOM cost for higher power. Thanks to the SPI programmability, one single hardware configuration can support various application platforms.

Features

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Single Chip

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Multiphase Booster

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High Overall Efficiency

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Minimum of External Components

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Active Input Filter with Low Current Ripple from Battery

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Integrated Boost Controller

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Programmable Input Current Limitation

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High Operating Frequencies to Reduce Inductor Sizes

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PCB Trace for Current Sense Shunt Resistor is Possible

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Low EMC Emission

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SPI Interface for Dynamic Control of System Parameters

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Fail Save Operating (FSO) Mode, Stand−Alone Mode

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Integrated Failure Diagnostic Typical Applications

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^{High Beam}

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^{Low Beam}

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DRL

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Position or Park Light

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Turn Indicator

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^Fog

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Static Cornering

www.onsemi.com

QFN24 MW SUFFIX CASE 485L

MARKING DIAGRAM

See detailed ordering and shipping information on page 34 of this data sheet.

ORDERING INFORMATION N703 = Specific Device Code or N78703

A = Assembly Location L or WL = Wafer Lot Y or YY = Year W or WW = Work Week G = Pb−Free Package

N703−1 ALYWG

G

(Note: Microdot may be in either location) 1 24

QFN24 MW SUFFIX CASE 485CS

24 1

Case 485L

N78703−0 AWLYYWWG

G Case 485CS

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TYPICAL APPLICATION SCHEMATIC

Figure 1. Typical Application Schematic

VBB

GND GNDP

ON Semiconductor LED driver 3 phase booster

NCV78703

C_BST_IN

ENABLE1,3

FSO/ENABLE2 VDRIVE

SPI_SCLK/TST2 SPI_SDI SPI_SDO SPI_SCS

mC V_Batt

VDD

(after rev. pol. prot.)

COMP

BSTSYNC/TST/TST1

PWR GND Sig GND

C_BB

C_DRIVE

C_DD R_BC1 C_BC1

C_BC2

L1 VGATE 1

IBSTSENSE 1+

IBSTSENSE 1−

L2 VGATE 2

C_BST VBOOSTDIV

Phase 1

Phase 2

Vboost

R_SENSE1

R_SENSE2

RD1

RD2 T1

T2 VCC of MCU

R_SDO

L3

Phase 3

R_SENSE3 VGATE 3 T3

IBSTSENSE 3+

IBSTSENSE 3−

IBSTSENSE 2+

IBSTSENSE 2−

Table 1. EXTERNAL COMPONENTS

Component Function Typ. Value Unit

L1, L2, L3 Booster regulator coil 10 mH

T1, T2, T3 Booster regulator switching transistor e.g. NTD6416ANL

D1, D2, D3 Booster regulator diode e.g. MBR5H100MFS

R_SENSE1, R_SENSE2,

R_SENSE3 Booster regulator current sensing resistor 10 mW

C_BST Booster regulator output capacitor 0.44 mF/W

C_BB VBB decoupling capacitance (Note 1) 1 mF

C_VDRIVE Capacitor for V_DRIVE regulator 1 mF

C_VDRIVE_ESR ESR of V_DRIVE capacitor max. 200 mW

C_DD V_DD decoupling capacitor 1 mF

C_DD_ESR ESR of V_DD capacitor max. 200 mW

R_SDO SPI pull−up resistor 1 kW

C_BC1 Booster compensation network See Booster Compensator Model section C_BC2 Booster compensation network See Booster Compensator Model section R_BC1 Booster compensation network See Booster Compensator Model section

RD1 Booster output voltage feedback divider (Note 2) 107 (±1% tolerance) kW RD2 Booster output voltage feedback divider (Note 2) 3.24 (±1% tolerance) kW 1. The value represents a potential initial startup value on a generic application. The actual size of the boost capacitor depends on the

application defined requirements (such as power level, operating ranges, number of phases) and transient performances with respect to the rest of BOM. Please refer to application notes and tools provided by ON Semiconductor for further guidance. The chosen value must be validated in the application.

2. Proposed values. Divider ratio (BSTDIV_RATIO) has to be 34. Tolerance of the resistors has to be ±1% to guarantee Booster parameters (see Table 12).

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Figure 2. Block Diagram LDR

LDR

Predriver

Current sense CMP PWM

Vdrive Vref

Error amplifier

VBOOSTDIV

Comp

VGATE 1 IBSTSENSE 1+

IBSTSENSE 1−

Predriver

Vdrive

IBSTSENSE 2−

VDRIVE DIV

VDD VBB

Bandgap Vref POR

Bias

TSD

OSC

5V tolerant input BSTSYNC,

ENABLE1,2,3, TST1/TST2

5V tolerant input / OD output

Digital control

SPI

GND GNDP

Booster

OTP

Predriver

Vdrive

IBSTSENSE 3−

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PACKAGE AND PIN DESCRIPTION

2 3 4 1

6 5

22 23

24 21 20 19

15 16 17 18

13 14

7 8 9 10 11 12

GNDVBB VDD COMP VBOOSTDIV

ENABLE1

FSO/ ENABLE2 BSTSYNC/

TST/TST1

SDO

SDI

CSB/SCS

SCLK/

TST2

GNDP IBST SENSE2−

IBST SENSE2+

IBST SENSE1−

IBST SENSE1+

IBST IBST VGATE3 VGATE2 VGATE1

VDRIVE

ENABLE3

NCV78703

Figure 3. Pin Connections – QFN24 5x5 and QFN24 4x4

SENSE3+

SENSE3−

Table 2. PIN DESCRIPTION

Pin No. QFN24 Pin Name Description I/O Type

1 ENABLE3 ENABLE3 input MV in

2 VGATE1 Booster MOSFET gate pre−driver MV out

5 IBSTSENSE3+ Coil3 current positive feedback input MV in

6 IBSTSENSE3− Coil3 current negative feedback input MV in

7 GNDP Power ground Ground

12 FSO/ENABLE2 FSO/ENABLE2 input MV in

13 SCLK/TST2 SPI clock / TST2 IO MV in

14 CSB/SCS SPI chip select (chip select bar) MV in

15 SDI SPI data input MV in

16 SDO SPI data output – pull up MV open−drain

17 BSTSYNC/TST/TST1 External clock for the boost regulator/ TM entry/ TST1 IO HV in

18 ENABLE1 ENABLE1 input MV in

19 VBOOSTDIV Booster high voltage feedback input HV in

20 COMP Compensation for the Boost regulator LV in/out

21 GND Ground Ground

22 VDD 3 V logic supply LV supply

23 VDRIVE 10 V supply MV supply

24 VBB Battery supply HV supply

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Table 3. ABSOLUTE MAXIMUM RATINGS

Characteristic Symbol Min Max Unit

Battery supply voltage (Note 4) VBB −0.3 36 (Note 3) V

Logic supply voltage (Note 5) V_DD −0.3 3.6 V

Gate driver supply voltage (Note 6) V_DRIVE −0.3 12 V

Input current sense voltage (Note 7) IBSTSENSEPx,

IBSTSENSENx −1.0 12 V

Medium voltage IO pins (Note 8) IOMV −0.3 6.5 V

Storage Temperature (Note 9) T_STRG −50 150 °C

Electrostatic Discharge on Component Level (Note 10) Human Body Model

Charge Device Model VESD_HBM

V_{ESD_CDM} −2

−500 +2

+500 kV

V Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected.

3. Absolute maximum rating for VBB is 40 V for limited time < 0.5 s

4. Absolute maximum rating for pins: VBB, BSTSYNC/TST/TST1, VBOOSTDIV 5. Absolute maximum rating for pins: VDD, COMP

6. Absolute maximum rating for pins: VDRIVE, VGATE1, VGATE2, VGATE3

7. Absolute maximum rating for pins: IBSTSENSE1+, IBSTSENSE1−, IBSTSENSE2+, IBSTSENSE2−, IBSTSENSE3+, IBSTSENSE3−

8. Absolute maximum rating for pins: SCLK/TST2, CSB, SDI, SDO, ENABLE1, FSO/ENABLE2, ENABLE3 9. For limited time up to 100 hours. Otherwise the max storage temperature is 85°C.

10.This device series incorporates ESD protection and is tested by the following methods:

ESD Human Body Model tested per EIA/JESD22−A114 ESD Charge Device Model tested per ESD−STM5.3.1−1999

Latch−up Current Maximum Rating: v100 mA per JEDEC standard: JESD78

Operating ranges define the limits for functional operation and parametric characteristics of the device. A mission profile (Note 11) is a substantial part of the

operation conditions; hence the Customer must contact ON Semiconductor in order to mutually agree in writing on the allowed missions profile(s) in the application.

Table 4. RECOMMENDED OPERATING RANGES

Characteristic Symbol Min Typ Max Unit

Battery supply voltage (Note 12 and 13) V_BB 5 30 V

Logic supply voltage (Note 14) V_DD 3.1 3.5 V

VDD current load I_DD 50 mA

Medium voltage IO pins IOMV 0 5 V

Input current sense voltage IBSTSENSEPx,

IBSTSENSENx −0.1 1 V

Functional operating junction temperature range (Note 15) T_JF −45 155 °C

Parametric operating junction temperature range (Note 16) T_JP −40 150 °C

Functional operation above the stresses listed in the Recommended Operating Ranges is not implied. Extended exposure to stresses beyond the Recommended Operating Ranges limits may affect device reliability.

11. A mission profile describes the application specific conditions such as, but not limited to, the cumulative operating conditions over life time, the system power dissipation, the system’s environmental conditions, the thermal design of the customer’s system, the modes, in which the device is operated by the customer, etc. No more than 100 cumulated hours in life time above T_tw.

12.Minimum VBB for OTP memory programming is 15.8 V.

13.VDRIVE is supplied from VBB, it must be verified that VDRIVE voltage is appropriate for the external FETs.

14.VBB > 5 V

15.The circuit functionality is not guaranteed outside the functional operating junction temperature range. Also please note that the device is verified on bench for operation up to 170°C but that the production test guarantees 155°C only.

16.The parametric characteristics of the circuit are not guaranteed outside the Parametric operating junction temperature range.

Table 5. THERMAL RESISTANCE

Characteristic Package Symbol Min Typ Max Unit

Thermal Resistance Junction to Exposed Pad (Note 17) QFN24 4x4 Rthjp 2.82 °C/W 17.Includes also typical solder thickness under the Exposed Pad (EP). Thermal resistance junction to PCB Top Layer.

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ELECTRICAL CHARACTERISTICS

Note: All Min and Max parameters are guaranteed over full battery voltage (5 V; 30 V) and junction temperature (T_JP) range (−40°C; 150°C), unless otherwise specified.

Table 6. TEMPERATURE MEASUREMENTS

Characteristic Symbol Conditions Min Typ Max Unit

Thermal Shutdown TSD 165 170 175 °C

Thermal Warning TW 155 160 165 °C

Thermal Output TEMP7 ADC_TEMP_THR[2:0] = 111 140 150 160 °C

Thermal Output Hysteresis TEMP_HYST 3 °C

Table 7. VDRIVE: 10 V SUPPLY FOR BOOST FET GATE DRIVER CIRCUIT

VDRIVE reg. voltage from VBB

(Note 18) VDRV_15 [VDRIVE_VSETPOINT =

1111], Vbb − VDRIVE > 0.5 V

@IDRIVE = 90 mA

9.7 10.1 10.7 V

VDRIVE reg. voltage from VBB

(Note 18) VDRV_00 [VDRIVE_VSETPOINT =

0000], Vbb − VDRIVE > 0.5 V @IDRIVE = 90 mA

4.8 5 5.3 V

VDRIVE increase per code (Note 18) DVDRV Linear increase, 4 bits 0.34 V

DC output current consumption VDRV_ILIM 0 90 mA

Output current limitation VDRV_BB_IL 90 500 mA

Output overload condition for

VDRIVE_NOK detection (Note 19) VDRIVE_NOK_ILOAD 95 mA

Minimum VBB−VDRIVE sufficient

voltage (Note 19) VDRIVE_NOK_VBBLOW 0.5 V

VDRIVE UV detection threshold

(Note 20) VDRV_UV_[7] Relative threshold to actual

VDRIVE_VSETPOINT {VDRIVE_UV_THR = 111]

83 87 91 %

79 83 87 %

75 79 84 %

71 75 79 %

63 67 71 %

18.The VDRIVE voltage drop between VDRIVE and VBB has to be sufficient (min. 0.5 V).

19.Both of these conditions have to be fulfilled otherwise SPI status bit VDRIVE_NOK is set.

20.Relative threshold to typical value of VDRIVE_VSETPOINT settings.

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Table 7. VDRIVE: 10 V SUPPLY FOR BOOST FET GATE DRIVER CIRCUIT

54 58 62 %

46 50 54 %

VDRIVE UV detection threshold VDRV_UV_[0] Relative threshold to actual VDRIVE_VSETPOINT {VDRIVE_UV_THR = 000]

0 %

VDRIVE UV detection delay VDRV_UV_DL 5 35 ms

18.The VDRIVE voltage drop between VDRIVE and VBB has to be sufficient (min. 0.5 V).

19.Both of these conditions have to be fulfilled otherwise SPI status bit VDRIVE_NOK is set.

20.Relative threshold to typical value of VDRIVE_VSETPOINT settings.

Table 8. VDD: 3 V LOW VOLTAGE ANALOG AND DIGITAL SUPPLY

VDD regulator output voltage V_DD Vbb > 5 V 3.135 3.465 V

DC output current consumption VDD_IOUT Vbb > 5 V, including 10 mA self

current consumption 50 mA

Output current limitation VDD_ILIM 60 350 mA

Table 9. POR: POWER−ON RESET CIRCUIT

POR Toggle level on VDD rising POR3V_H 2.55 3.05 V

POR Toggle level on VDD falling POR3V_L 2.3 2.8 V

POR Hysteresis POR3V_HYST 0.15 V

POR threshold on VBB, VBB rising POR_VBB_H Applicable only during startup

(VBB is rising) 3.8 4.3 V

Table 10. OTP MEMORY

Min. VBB for OTP zapping VBB_OTP 15.8 V

VBB range for OTP_FAIL flag during

OTP programming VBB_OTP_L 13.2 14.1 15 V

Table 11. OSC10M: SYSTEM OSCILLATOR CLOCK

System oscillator frequency FOSC10M 7 10 13 MHz

Table 12. BOOSTER (Note 21)

Booster overvoltage shutdown BST_OV_127 [BOOST_OVERVOLTSD_THR

=1111111], DC level 63.8 65.85 67.9 V Booster overvoltage shutdown BST_OV_022 [BOOST_OVERVOLTSD_THR

=0010110], DC level 11 11.5 12 V

Booster overvoltage shutdown

increase per code DBST_OV Linear increase, 7 bits 0.518 0.718 V

21.All parameters are guaranteed for recommended external Vboost resistor divider (Rdiv) ratio 34 with ±1% tolerance.

22.Higher levels are valid if BST_VLIMTH value 2 or 3 (BOOST_VLIMTHx[1] = 1) is selected at least on one channel.

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Booster overvoltage

re−activation BST_RA_3 [BOOST_OV_REACT =11], DV to

the Vboost reg. overvoltage protection, DC level

−1.9 −1.5 −1.1 V

Booster overvoltage

re−activation BST_RA_0 [BOOST_OV_REACT =00], DV to

the Vboost reg. overvoltage protection, DC level

0 V

Booster overvoltage re−activa-

tion decrease per code DBST_RA Linear decrease, 2 bits, DC level −0.6 −0.5 V

Booster undervoltage protection (external divider fail state detection)

BST_EA_UV 3.45 3.95 4.45 V

Booster undervoltage protection (external divider fail state detection) hysteresis

BST_EA_UV_HYST 0.6 V

Booster regulation level BST_REG_125 [BOOST_VSETPOINT =1111101],

DC level 62.8 64.8 66.8 V

Booster regulation level BST_REG_022 [BOOST_VSETPOINT =0010110],

DC level 11 11.5 12 V

Booster regulation level increase

per code DBST_REG Linear increase, 7 bits 0.518 0.718 V

Transconductance gain of Error

amplifier BST_EA_GM3 [BOOST_OTA_GAIN =11], seen

from VBOOST, DC value 63 90 117 mS

amplifier BST_EA_GM0 [BOOST_OTA_GAIN =00],

high impedance 0 mS

EA max output current EA_IOUT_POS 150 mA

EA min output current EA_IOUT_NEG −150 mA

Output leakage current in tri−state EA_ILEAK Output in tri−state (EA_GM0) −1 1 mA

EA output resistance EA_ROUT 2.0 MW

EA max output voltage_3 COMP_CLH_3 BOOST_SLPCTRL[2]=1,

OR of all BOOST_VLIMTHx[1]=1 2.1 2.26 V

OR of all BOOST_VLIMTHx[1]=0 1.98 V

EA min output voltage COMP_CLL 0.4 V

Booster VOOSTDIV pin input

pull up current BST_EA_DIV_INI Pull current source towards

to VDD voltage 0.4 0.8 1.4 mA

Division of COMP on the Current

comparator input COMP_DIV_15 [P_DISTRIBUTIONx =01111],

signed, see Power Distribution section and Table 19 for details

20

Division of COMP on the current

comparator input COMP_DIV_0 [P_DISTRIBUTIONx =00000],

signed, see Power Distribution section and Table 19 for details

6.81

Division of COMP on the current

comparator input COMP_DIV_−16 [P_DISTRIBUTIONx =11111], signed, see Power Distribution sec-

tion and Table 19 for details

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21.All parameters are guaranteed for recommended external Vboost resistor divider (Rdiv) ratio 34 with ±1% tolerance.

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Voltage shift on COMP on Cur-

rent comparator input COMP_VSF +0.5 V

Booster skip cycle for low cur-

rents (Note 22) BST_SKCL_3 [BOOST_SKCL =11], Booster dis-

abled for lower V(COMP) 0.7/0.8 V

VGATE comparator to start

BST_TOFF time BST_VGATE_THR_1 [VBOOST_VGATE_THR = 1] 1.2 V

VGATE comparator to start

BST_TOFF time BST_VGATE_THR_0 [VBOOST_VGATE_THR = 0] 0.4 V

Booster minimum OFF time BST_TOFF_7 [VBOOST_TOFF_SET = 111], time from VGATE below

VBOOST_VGATE_THR

780 1200 1620 ns

Booster minimum OFF time BST_TOFF_6 VBOOST_TOFF_SET = 110], time from VGATE below

VBOOST_VGATE_THR

300 460 620 ns

VBOOST_VGATE_THR

260 400 540 ns

VBOOST_VGATE_THR

220 340 460 ns

VBOOST_VGATE_THR

180 280 380 ns

VBOOST_VGATE_THR

140 220 300 ns

VBOOST_VGATE_THR

100 160 220 ns

VBOOST_VGATE_THR

60 100 140 ns

Booster minimum ON time BST_TON_7 [VBOOST_TON_SET =111], time

from internal signal for VGATE drive 330 530 730 ns Booster minimum ON time BST_TON_6 [VBOOST_TON_SET =110], time

from internal signal for VGATE drive 120 180 240 ns 21.All parameters are guaranteed for recommended external Vboost resistor divider (Rdiv) ratio 34 with ±1% tolerance.

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Table 13. BOOSTER – CURRENT REGULATION AND LIMITATION

Current comparator for Imax de-

tection BST_VLIMTHx_3 [BOOST_VLIMTHx =11], DC

level of threshold voltage 95 100 105 mV Current comparator for Imax de-

level of threshold voltage 75 80 85 mV

Current comparator for Imax de-

level of threshold voltage 57 62.5 67 mV Current comparator for Imax de-

level of threshold voltage 45 50 55 mV

Current comparator for Vboost

regulation, offset voltage BST_OFFS −10 10 mV

Booster slope compensation BST_SLPCTRL_7 BOOST_SLPCTRL =111], see

Power Distribution section 290 /

COMP_DIV mV/ ms

COMP_DIV mV/ ms Booster slope compensation BST_SLPCTRL_5 BOOST_SLPCTRL =101], see

COMP_DIV mV/ ms

Power Distribution section 0 mV/ ms

Sense voltage common mode

range CMVSENSE Over full operating range −0.1 1 V

Table 14. BOOSTER – PRE−DRIVER

High−side switch impedance RONHI t = 25°C 4.2 W

High−side switch impedance RONHI t = 150°C 6 7 W

Low−side switch impedance RONLO t = 25°C 4.2 W

Low−side switch impedance RONLO t = 150°C 6 7 W

Pull down resistor on VGATEx RPDOWN 10 kW

Table 15. 5 V TOLERANT DIGITAL INPUTS (SCLK/TST2, CSB, SDI, BSTSYNC/TST/TST1, ENABLE1, FSO/ENABLE2, ENABLE3)

High−level input voltage VINHI SDI, BSTSYNC, CSB and SCLK/TST2 2 V

Low−level input voltage VINLO SDI, BSTSYNC, CSB and SCLK/TST2 0.8 V

Pull resistance (Note 23) Rpull SDI, BSTSYNC, CSB and SCLK/TST2 40 160 kW

High−level input voltage ENA_VINHI ENABLE1, FSO/ENABLE2, ENABLE3 2.35 V

Low−level input voltage ENA_VINLO ENABLE1, FSO/ENABLE2, ENABLE3 0.7 V

Pull resistance (Notes 23 and 24) ENA_Rpull ENABLE1, FSO/ENABLE2, ENABLE3 20 400 kW 23.Internal pull down resistor (Rpd) for SDI, ENABLE1, FSO/ENABLE2, ENABLE3, BSTSYNC and SCLK/TST2, pull up resistor (Rpu) for CSB

to VDD.

24.VDD > POR3V_H; ENA_Rpull > 20 kW when VDD = 0 V to 3.5 V

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Table 16. 5 V TOLERANT OPEN−DRAIN DIGITAL OUTPUT (SDO)

Low−voltage output voltage VOUTLO Iout = −10 mA (current flows into the pin) 0.4 V

Equivalent output resistance RDSON Lowside switch 20 40 W

SDO pin leakage current SDO_ILEAK 2 mA

SDO pin capacitance (Note 25) SDO_C 10 pF

CLK to SDO propagation delay SDO_DL Low−side switch activation/deactivation time;

@1 kW to 5 V, 100 pF to GND, for falling edge V(SDO) goes below 0.5 V

60 ns

25.Guaranteed by bench measurement, not tested in production.

Table 17. SPI INTERFACE

Characteristic Symbol Min Typ Max Unit

CSB setup time t_CSS 0.5 ms

CSB hold time tCSH 0.25 ms

SCLK low time tWL 0.5 ms

SCLK high time tWH 0.5 ms

Data−in (DIN) setup time, valid data before rising edge of CLK tSU 0.25 ms

Data−in (DIN) hold time, hold data after rising edge of CLK tH 0.275 ms

Output (DOUT) disable time (Note 26) tDIS 0.07 0.32 ms

Output (DOUT) valid (Note 26) tV1→0 0.32 ms

Output (DOUT) valid (Note 27) t_V0→1 0.32 + t(RC) ms

Output (DOUT) hold time (Note 26) tHO 0.07 ms

CSB high time tCS 1 ms

26.SDO low–side switch activation time

27.Time depends on the SDO load and pull–up resistor

DIN 15 VIL

VIH

VIL VIH

VIH

DOUT 15 DOUT 14 DOUT 13 DOUT 1 DOUT 0

DIN 14 DIN 13 DIN 1 DIN 0

VIL VIH

VIL

tCSS

tWH tWL tCSH

tCS

tSU tH

tV tHO tDIS

HI−Z HI−Z

CSB

SCLK

DIN

DOUT

Initial state of SCLK after CSB falling edge is don’t care , it can be low or high

Figure 4. SPI Communication Timing

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Typical Characteristics

Figure 5. Typical temperature dependency of VGATE high and low side switch impedances

DETAILED OPERATING DESCRIPTION Supply Concept in General

Low operating voltages become more and more required due to the growing use of start stop systems. In order to respond to this necessity, the NCV78703 is designed to support power−up starting from VBB = 5 V.

Figure 6. Cranking Pulse (ISO7637−1): System has to be fully functional (Grade A) from Vs = 5 V to 28 V VDRIVE Supply

The VDRIVE supply voltage represents the power for the complete booster pre−driver block which generates the VGATE, used to switch the booster MOSFETs. The voltage is programmable via SPI in 16 different values (register VDRIVE_VSETPOINT[3:0], ranging from a minimum of 5 V typical to 10.1 V typical: see Table 7). This feature allows having the best switching losses vs. resistive losses trade off, according to the MOSFET selection in the

application, also versus the minimum required battery voltage.

VDRIVE supply takes its energy from VBB battery voltage. Minimal VDRIVE regulator voltage drop is about 0.5 V. To ensure that booster can be operated close to minimal VBB battery voltage, logic level MOSFETs should be considered. By efficiency reasons, it is important to select MOSFETs with low gate charge. External MOSFETs are

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controlled by the integrated pre−driver with slope control to reduce EMC emissions.

VDRIVE Undervoltage Lockout safety mechanism monitors sufficient voltage for MOSFETs and protects them by switching off the booster when VDRIVE voltage is too low. During initial 150 μs after POR the detection is disabled to ensure that normal operating mode is entered. Detection level is set by VDRIVE_UV_THR[2:0] register relatively to used VDRIVE voltage. Detection thresholds are summarized in Table 7. When VDRIVE_UV_THR[2:0] = 0, function is disabled.

VDD Supply

The VDD supply is the low voltage digital and analog supply for the chip and derives energy from VBB. Due to the low dropout regulator design, VDD is guaranteed already from low VBB voltages.

The Power−On−Reset circuit (POR) monitors the VDD and VBB voltages to control the out−of−reset condition at power−up. At least one ENABLE input is required to be in logic ‘1’ to enable the VDD regulator and leave reset state.

When SPI register VDD_ENA is set to ‘1’, VDD regulator stays enabled and chip stays in normal mode, even if all ENABLEx (x = 1, 2) inputs are set to logic ‘0’. When SPI register VDD_ENA is set to ‘0’ and all ENABLEx inputs are set to logic ‘0’, chip enters the reset state and VDD regulator is switched off.

VDD regulator is dimensioned to supply up to 8 NCV78713/NCV78723 buck devices.

Internal Clock Generation – OSC10M

An internal RC clock named OSC10M is used to run all the digital functions in the chip. The clock is trimmed in the factory prior to delivery. Its accuracy is guaranteed under full operating conditions and is independent from external component selection (refer to Table 11 for details). All timings depend on OSC10M accuracy.

Boost Regulator General

The booster stage provides the required voltage source for the LED string voltages out of the available battery voltage.

Moreover, it filters out the variations in the battery input current in case of LED strings PWM dimming.

For nominal loads, the boost controller will regulate in continuous mode of operation, thus maximizing the system power efficiency at the same time having the lowest possible

input ripple current (with “continuous mode” it is meant that the supply current does not go to zero while the load is activated). Only in case of very low loads or low dimming duty cycle values, discontinuous mode can occur: this means the supply current can swing from zero when the load is off, to the required peak value when the load is on, while keeping the required input average current through the cycle. In such situations, the total efficiency ratio may be lower than the theoretical optimal. However, as also the total losses will at the same time be lower, there will be no impact on the thermal design.

On top of the using phases available in the device, the device can be combined with more NCV78702/NCV78703 devices in the application to gain even more phases. More details about the multichip−multiphase mode can be found in the dedicated section.

Booster Regulation Principles

The NCV78703 features a current−mode voltage boost controller, which regulates the VBOOST line used by the buck converters. The regulation loop principle is shown in the following picture. The loop compares the reference voltage (BOOST_VSETPOINT) with the actual measured voltage at the VBOOST pin, thus generating an error signal which is treated internally by the error trans−conductance amplifier (block A1). This amplifier transforms the error voltage into current by means of the trans−conductance gain Gm. The amplifier’s output current is then fed into the external compensation network impedance (A2), so that it originates a voltage at the VCOMP pin, this last used as a reference by the current control block (B).

The current controller regulates the duty cycle as a consequence of the VCOMP reference, the sensed inductor peak current via the external resistor RSENSE and the slope compensation used. The power converter (block C) represents the circuit formed by the boost converter externals (inductor, capacitors, MOSFET and forward diode). The load power (usually the LED power going via the buck converters) is applied to the converter. The controlled variable is the boost voltage, measured directly at the device VBOOST pin with a unity gain feedback (block F). The picture highlights as block G all the elements contained inside the device. The regulation parameters are flexibly set by a series of SPI commands. A detailed internal boost controller block diagram is presented in the next section.

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Figure 7. NCV78703 Boost Control Loop – Principle Block Diagram

Boost Controller Detailed Internal Block Diagram A detailed NCV78703 boost controller block diagram is provided in this section. The main signals involved are indicated, with a particular highlight on the SPI programmable parameters.

The blocks referring to the principle block diagram are also indicated. In addition, the protection specific blocks can be found (see dedicated sections for details).

Figure 8. Boost Controller Internal Detailed Block Diagram

COMP_CLH

COMP_CLL BOOST_SLPCTRL[1]

BOOST_VLIMTH[1]

EA

SKCL

BOOST_VLIMTH[1]

BOOST_SKCL[1:0]

BOOST_VSETPOINT[6:0]

VBOOST

Internal connection of other phases

Current peak trigger (duty cycle regulation) Skip Cycle

COMP

1 k

Ireg k

1

BOOST_VLIMTH[1:0]

Imax

P_DISTRIBUTIONx[4:0]

Vshift = 0.5V Slope compensation

BOOST_SLPCTRL[2:0]

COMP_VSF

IMAX

VBAT

VGATE

Rsense IBSTSENSE+

L

IBSTSENSE-

D

COUT

RD1 RD2

R_BC1 C_BC1 C_BC2

COMP VBOOSTDIV

TOFF generator

TON generator

R S rst BOOSTx_SYNC

VBOOST_TOFF_SET[2:0]

Ireg Imax

VBOOST_TON_SET[2:0]

UV OV/RA BOOST_OVERVOLTSD_THR[6:0]

BOOST_OV_REACT[1:0]

Skip Cycle

1 BOOST_TOFF

VGATE

Error Ampliﬁer

PWM Control 1, 2, 3

Digital Control 1, 2, 3

AND

VBOOST_VGATE_THR VGATE VGATE Low

COMP_DIV_ratio = 4 ÷ 20 COMP_DIV_ratio = 4 ÷ 20

BOOST_TON

OR OR

OR AND

1

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Figure 9. Boost Controller Internal Waveforms

BOOSTx_SYNC [1,2,3]

Ireg or Imax cmp [1,2,3]

BOOST_TOFF [1,2,3]

BOOST_TON [1,2,3]

GATE [1,2,3]

VGATE_LOW [1,2,3]

Min TOFF Min TON

Pulse masked during min TON

ON time by BOOST _SYN signal

Min TOFF GATE reset Pulse masked

during min TON

Min TON Min TON

Min TOFF

OFF time by BOOST _SYN si g.

& VGATE comp. & TOFF gen.

ON time by TON generator ON time by IREG /IMAX comp.

OFF time by IREG /IMAX comp. & TOFF generator

Booster Regulator Setpoint (BOOST_VSETPOINT) The booster voltage VBOOST is regulated around the target programmable by the 7−bit SPI setting BOOST_VSETPOINT[6:0], ranging from a minimum of 11.5 V to a maximum of typical 64.8 V (please refer to Table 12 for details). Due to the step−up only characteristic of any boost converter, the boost voltage cannot obviously be lower than the supply battery voltage provided. Therefore a target of 11.5 V would be used only for systems that require the activation of the booster in case of battery drops below the nominal level. At power−up, the booster is disabled and the setpoint is per default the minimum (all zeroes).

Booster Overvoltage Shutdown Protection

An integrated comparator monitors VBOOST in order to protect the external booster components from overvoltage.

When the voltage rises above the threshold defined by the BOOST_OVERVOLTSD_THR[6:0], ranging from a minimum 11.5 V to a maximum of typical 65.85 V (please refer to Table 12 for details), the MOSFET gate is switched−off at least for the current PWM cycle and at the same time, the boost overvoltage flag in the status register will be set (BOOST_OV = ‘1’), together with the

BOOSTx_STATUS flags equal to zero. The PWM runs again as from the moment the VBOOST will fall below the reactivation hysteresis defined by the BOOST_OV_REACT[1:0] SPI parameter. Therefore, depending on the voltage drop and the PWM frequency, it might be that more than one cycle will be skipped. A graphical interpretation of the protection levels is given in the figure below, followed by a summary table (Table 18).

BOOST_VSETPOINT [V]

(BOOST_OVERVOLTSD_THR - BOOST_OV_REACT) (BOOST_OVERVOLTSD_THR)

Boost overvoltage reactivation Boost overvoltage shutdown

Figure 10. Booster voltage protection levels with respect to the setpoint

Table 18. BOOST OVERVOLTAGE PROTECTION LEVES AND RELATED DIAGNOSTIC

Case Condition PWM gate control

SPI flags

BOOSTx_STATUS BOOST_OV

A V_BOOST < BOOST_VSETPOINT Normal (not disabled) 1 0

B V_BOOST > BOOST_OVERVOLTSD_THR Disabled until case ‘C’ 0 1 (latched)

C V_BOOST < BOOST_OVERVOLTSD_THR −

BOOST_OV_REACT Re−enables the PWM,

normal mode resumed if from case ‘B’

1 1 (latched, if read in this condition, it will go back to ‘0’

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Booster Current Regulation Loop

The peak−current level of the booster is set by the voltage of the compensation pin COMP, which is output of the trans−conductance error amplifier, “block B” of Figure 7.

This reference voltage is fed to the current comparator via a divider (divider ratio of which can be set by Power sharing function for each phase independently, see “Power Distribution” section for more details. The comparator compares this reference voltage with voltage VSENSE sensed on the external sense resistor RSENSE, connected to the pins IBSTSENSE1/2/3+ and IBSTSENSE1/2/3−. The sense voltage is created by the booster inductor coil current when

the MOSFET is switched on and is summed up to an additional offset of +0.5 V (see COMP_VSF in Table 12) and on top of that, a slope compensation voltage ramp is added. The slope compensation is programmable by SPI via the BOOST_SLPCTRL[2:0] register and can also be disabled. Due to the offset, current can start flowing in the circuit when VCOMP > COMP_VSF.

When booster is active, voltage at COMP pin is clamped to voltage between 0.4 V (see Table 12) and 1.35 V to 2.26 V depending on BOOST_VLIMTHx and BOOST_SLPCTRL settings (see Table 13) to ensure quicker reaction of the system to load changes.

COMP 1

1

1 K1

IBSTSENSE1+

VGATE1

COMP

SLOPE GENERATOR COMP_VSF

VIN1

VOUT

K1

BOOST_SLPCTRL[2:0]

L1 D1

RSENSE1

COUT

Dx

IBSTSENSE1−

Internal connection of next phase

Current peak reached trigger (duty cycle regulation) IOUT

IL1

VCOMP

DEVICE

EXTERNAL COMPONENTS

VSENSE= ILx RSENSE

Booster phase 1 Booster phase x

Figure 11. Booster Peak Current Regulator Involved in the Current Control Loop Booster Current Limitation Protection

On top of the normal current regulation loop comparator, an additional comparator clamps the maximum physical current that can flow in the booster input circuit while the MOSFET is driven. The aim is to protect all the external components involved (boost inductor from saturation, boost diode and boost MOSFET from overcurrent, etc...). The protection is active PWM cycle−by−cycle and switches off the MOSFET gate when V_SENSE reaches its maximum threshold defined by the BOOST_VLIMTHx[1:0] register (see Table 13 for more details). Therefore, the maximum allowed peak current will be defined by the ratio IPEAK_MAX

= BOOST_VLIMTHx[1:0]/RSENSE. The maximum current must be set in order to allow the total desired booster power for the lowest battery voltage. Warning: setting the current limit too low may generate unwanted system behavior as uncontrolled de−rating of the LED light due to insufficient power.

Booster PWM Internal Generation

Internally generated booster PWM signal is used only in FSO modes. When FSO mode is entered, booster PWM

source is switched automatically from the external BSTSYNC pin to the internally generated signal, which is derived from the internal oscillator OSC10M. A selection of the frequencies is enabled by the register FSO_BST_FREQ[2:0], ranging from typical 200 kHz to typical 1 MHz (Table 22).

Booster PWM External Generation

In normal operation mode the booster PWM is taken directly from the BSTSYNC device pin. Maximum frequency at the BSTSYNC pin is 1 MHz. There is no actual limitation in the resolution, apart from the system clock for the sampling and a debounce of two clock cycles on the signal edges. The gate PWM is synchronized with either the rising or falling edge of the external signal depending on the BOOST_SRCINV bit value. The default POR value is “0”

and corresponds to synchronization to the rising edge.

BOOST_SRCINV equals “1” selects falling edge synchronization. Thanks to the possibility to invert external clock in the chip by SPI, up to 6−phase systems with shifted clock are supported with only 1 external clock.

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Figure 12. Generation of BOOSTx_SYNC BSTSYNC pin

MUX Debounce

PWM internal generation (FSO mode)

Normal / FSO mode

BOOST_SRCINV (SPI)

DIV BY 2 or 3 SPI TSD SPI TW

1 0

MUX 0

1

BOOST1_SYNC_INT BOOST2_SYNC_INT

COMB.

BOOST1_EN (SPI)

BOOST1_SYNC

BOOST3_SYNC_INT

BOOST_DIV3/DIV2 (SPI)

Figure 13. PWM Generation (2−phase and 3−phase)

DIV BY 2

BSTSYNC input

BOOST1_SYNC_INT

BOOST2_SYNC_INT

BOOST3_SYNC_INT

Disabled

DIV BY 3

BSTSYNC input

BOOST1_SYNC_INT

BOOST2_SYNC_INT

BOOST3_SYNC_INT

BOOST_DIV3/DIV2 = `0'

BOOST_DIV3/DIV2 = `1'