BQ76PL455APFCT datasheet(113/125 Pages) TI1

113 / 125 page

GND

4.7 µF

50 V

C36

0.39

R23

150 V

Q17

ZXTN4004KTC

VP1

1.00

R78

1.00

R80

VP1

NPN_BASE

GND

1 µF

C40

BAT16

2512

200

R163

2512

200

R164

113

bq76PL455A

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SLUSCL0A – SEPTEMBER 2016 – REVISED OCTOBER 2016

Product Folder Links: bq76PL455A

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9 Power Supply Recommendations

The bq76PL455A is powered from the same cells it monitors. The bq76PL455A generates the additional VP and

VDIG supplies used in operation from this input. For best performance, use the following guidelines for

component selection.

9.1 NPN LDO Supply

VP1 is the input for the external LDO supply for the bq76PL455A. Figure 39 shows the typical circuit.

Figure 39. Power Supply Schematic

Select the NPN Transistor based on the following criteria:

1. Collector-Emitter Breakdown Voltage (BVCEO) > 100 V (or the module voltage plus any derating)

2. DC gain (β or approximately equal to hfe (AC gain)) > 100 at the expected load current

3. Collector-base capacitance < 35 pF at typical base-voltage range

4. Power handling > 500 mW (this assumes a 1-kΩ resistance in series with the collector)

5. Current handling > 100 mA

The series resistors R163 and R164 in Figure 39 serve several purposes:

1. Limit the current in the event of a fault

2. Shift some constant power dissipation in the regulator away from the transistor onto the resistor

3. Combine with the input capacitor on the transistor collector to serve as a filter

To calculate the required resistance, use Equation 17:

where

•

VCE(SAT) = VCE min at VBE(on), from transistor datasheet.

•

31mA is the bq79PL455A maximum inrush current at startup.

•

ILOAD is the expected current for any non-bq76PL455A external loads applied to the VP pin.

(17)

BQ76PL455APFCT Datasheet(PDF) 113 Page - Texas Instruments

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