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ON Semiconductor and the ON Semiconductor logo are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries. ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of ON Semiconductor’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent-Marking.pdf. ON Semiconductor reserves the right to make changes without further notice to any products herein. ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information provided by ON Semiconductor. “Typical” parameters which may be provided in ON Semiconductor data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. ON Semiconductor does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are not designed, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use ON Semiconductor products for any such unintended or unauthorized application, Buyer shall indemnify and hold ON Semiconductor and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that ON Semiconductor was negligent regarding the design or manufacture of the part. ON Semiconductor is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.

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www.fairchildsemi.com

Rev. 1.0.0 • 7/18/12

Fairchild Semiconductor Power33 Package Power MOSFET Solution in Multi-Cell

Battery Protection Applications

1. Introduction

This paper introduces Power33 MOSFET package technology from Fairchild Semiconductor. Small Power33 packaging provides extremely low resistance, reduces power loss, and provides thermally-enhanced performance. This note compares the Power33 package to SO-8 packages through a review of MOSFET technology and performance comparison in multi-cell battery-protection applications.

Smart battery safety circuits consist of a battery protection circuit and a run-time prediction and communication IC with one or more cells in series. They are designed to provide protection for battery packs by using a pair of MOSFET switches with a common drain. For laptops with a lithium ion (Li-Ion) battery, P-channel MOSFET devices have been the dominant solution, but N-channel MOSFET devices are becoming popular because of their lower RSP

(die size x RDS(ON)). An N-channel MOSFET normally has higher mobility, allowing it to achieve lower RDS(ON) with the same die size.^[1] It can reduce the power MOSFET footprint, enabling the Battery Management Unit (BMU) design to be size-optimized.

2. Overview of Multi-Cell Battery Protection Circuit Module (PCM)

Figure 1 and Figure 2 show a simplified battery-pack configuration and charge/discharge profile. Li-Ion multi-cell battery packs usually use a constant current and constant voltage method for charging operations. Once the Li-Ion cell voltage has charged to an internally set 4.2V level, the system begins to reduce the current to maintain the desired floating voltage while changing to constant voltage operation. For discharging operations, this process is reversed. To prevent over-charging or a drop in cell voltage (cell damage level), protection ICs set the maximum and under-voltage limits (internal voltage reference) that protect the system as well as the battery pack.

Figure 1. 3-Cell Battery-Pack Configuration

Figure 2. Li-Ion Charge / Discharge Profile

3. MOSFET Requirement in PCM

A MOSFET’s key requirements in PCM are summarized and compared with a switching power MOSFET in notebook applications, as shown in Table 1.

The selection of a power MOSFET in PCM depends on many factors and the importance of each of them to the design. These include:

Lower RDS(ON): Enables Extended Battery Life (EBL) and higher circuit efficiency.

Pulse Current Capability: This is critical to meet 200A/ms pulse current discharging specifications established by battery-pack manufacturers from a silicon - package aspect.

Smaller Package with Lower RΘJA: Enables the PCM to use less board space and improves thermal performance.

Voltage Capacity

Current

Cell Voltage (V) Capacity (% percent)

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AN-9762 APPLICATION NOTE

Rev. 1.0.0 • 7/18/12 2

Table 1. MOSFET Requirement by Applications

▲ Required / ● Critical Notebook PCM

BVDSS ▲ ●

Pulse Current Capability ^▲ ^●

RΘJA ▲ ●

Size ▲ ●

ESD ^● ^●

On Resistance, RDS(ON) ● ● Parasitic L, C (Ls/Lg or Cgs/Cgd/Cds) ● ▲

4. Thermally-Enhanced Power33 Package Solution

As batteries get smaller and thinner, the protection circuits attached to the battery cells should follow suit.^[2] An SO-8 package power MOSFET has been the main player for Li- Ion battery-protection circuits. However, its thermal capability, RDS(ON), and size constraints are at their limit because of the SO-8 package’s lead construction. To meet power density and size constraints, many power semiconductor manufacturers have increased the silicon power density and introduced new packages, such as Power56 and Power33, as shown Figure 3.

Figure 3. RSP and Package Trend

To meet the demand for higher power density devices in smaller packages, Fairchild Semiconductor offers a variety of 30V Power33 products to replace SO-8-packaged devices, as shown in Table 2.

Table 2. Fairchild 30V Product Portfolios Number of Products

with R_DS(ON)≤6mΩ

Package Type SO-8 Power56 Power33 When considering changing package type, engineers must take into account the change in MOSFET RDS(ON) associated with the size, as well as the thermal capability of the package. Table 3 shows the internal structures of each package. The Power Quad Flat No-Lead (PQFN) package has superior thermal capability compared to an SO-8 because of the leadless and exposed bottom area that provides a direct thermal path and lower thermal resistance when the device is mounted to PCB.

Table 3. Footprint Area Comparison

Type Area RΘJA

(1in², 2oz Board)

3D View

SO-8

30mm² 60°C/W

Power56

30mm² 50°C/W

Power33 10.9mm² 53°C/W

The lower thermal resistance (RΘJA, junction–to-ambient) in steady-state condition represents higher drain current and power dissipation, which results in much more efficient system design. A Power33-packaged device occupies less than half the footprint area of an SO-8 package, which allows design of a smaller PCM board.

5. Thermal Performance Verification

Verification was conducted to compare the thermal performance between industry-standard Power33 and SO-8 packages. To highlight the effect of the package type on battery protection circuits, two similar RDS(ON) power MOSFET pairs were chosen, as shown in Table 4.

Table 4. 30V MOSFET Parameter Package Typ. RDS(ON)

RΘJA (1in², 2oz

Board)

ID[A]

SO-8 3.8mΩ 60°C/W 18.5 Power33 3.6mΩ 53°C/W 18.8 The thermal capability evaluation method used complies with the three-series cell discharging condition, which has a 9V cell voltage and 7A, 8A, 9A, and 10A; which is considered the worst-case discharging condition on a double-side FR-4 PCB. The graph in Figure 4 compares the power dissipation performance of a Power33 package to that of an SO-8 package on a PCM evaluation board. Power dissipation steps in each device and the case temperature were measured. The Power33 package shows similar thermal performance at all reference points in spite of its smaller package size.

Power Dissipation (W)

Figure 4. Thermal Performance, SO-8 vs. Power33

Case Temperature (°C)

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AN-9762 APPLICATION NOTE

Rev. 1.0.0 • 7/18/12 3

6. Design Guidelines for Power33 Package

This section discusses the guidelines for using a device in the Power33 package.

Figure 5 shows a board space comparison between the SO-8 and Power33 packages. The Power33 package enables board-space savings of up to 70 percent.

Figure 5. Real PCM Board

The application note AN-9040 — Assembly Guidelines for Power33 Packaging^[3] provides information on Power33 packages’ ability to achieve SO-8-type performance in a small form factor. Due to the smaller package size, it is necessary for designers to be aware of stencil and via design, which can allow the engineer to achieve 25 percent or less voiding for Power33 packages, as shown in Figure 6.

Figure 6. Assembly Guideline

Table 5 provides information on Fairchild’s Power33 packaged MOSFETs by PCM power dissipation of less than 70°C, the case-temperature limit. Design engineers working on battery-pack protection should select a power MOSFET based on thermal capability for circuit efficiency.

Table 5. 30V N-Channel Selection Guide by Power Dissipation

Part No. Typ. RDS(ON)

(10VGS [mΩ])

Battery Pack PdMAX

(TC < 70°C at 25°C)

FDMC7660 1.8 90W

FDMC7664 3.6 80W

FDMC7672 4.3 70W

FDMC7678 5.3 60W

FDMC7692 7.2 <50W

7. Conclusion

The low-profile Power33-packaged MOSFET performance for battery protection has been demonstrated and compared to SO-8-packaged devices. By minimizing thermal rise and saving board space, while keeping the RDS(ON) low and allowing same-current capability; this package simplifies PCM board design.

Author

Dongsup Eom – LV Applications Engineer

References

[1] “Bi-Directional FlipFET MOSFETs for Cell Phone Battery Protection Circuits”, Mark Pavier, Hazel Schofield, Tim Sammon, Aram Arumanyan, Ritu sodi, PCIM 2001.

[2] “New Thermally Enhanced Packages for Power MOSFETs in Battery Applications”, Yalcin Bulut. IEEE 2004.

[3] “AN-9040 Assembly Guidelines for Power33 Packaging”, Dennis Lang, Fairchild Semiconductor.

DISCLAIMER

FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION, OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.

LIFE SUPPORT POLICY

FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION.

As used herein:

1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user.

2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.

10.9mm² 30mm²

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ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries.

ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of ON Semiconductor’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. ON Semiconductor reserves the right to make changes without further notice to any products herein.

ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.

Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information provided by ON Semiconductor. “Typical” parameters which may be provided in ON Semiconductor data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. ON Semiconductor does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are not designed, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use ON Semiconductor products for any such unintended or unauthorized application, Buyer shall indemnify and hold ON Semiconductor and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that ON Semiconductor was negligent regarding the design or manufacture of the part. ON Semiconductor is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.

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