Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsPMICsPMIC - battery management Charge management, Surge/undervoltage protection Li-Ion VQFN 20

Not Recommended for New Designs

bq24725

SLUS702A –JULY 2010–REVISED NOVEMBER 2010

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Table 8. Component List for Typical System Circuit of Figure 1 (continued)

PART DESIGNATOR QTY DESCRIPTION

Csys 1 Capacitor, Electrolytic, 220µF, 25V

D1 1 Diode, Schottky, 30V, 200mA, SOT-23, Fairchild, BAT54

D2 1 Diode, Dual Schottky, 30V, 200mA, SOT-23, Fairchild, BAT54C

Q1, Q2, Q5 3 N-channel MOSFET, 30V, 12.5A, SO-8, Fairchild, FDS6680A

Q3, Q4 2 N-channel MOSFET, 30V, 12A, PowerPAK 1212-8, Vishay Siliconix, SiS412DN

Q6 1 N-channel MOSFET, 50V, 0.2A, SOT-323, Diodes, BSS138W

L1 1 Inductor, SMT, 4.7µH, 5.5A, Vishay Dale, IHLP2525CZER4R7M01

R1 1 Resistor, Chip, 430kΩ, 1/10W, 1%, 0603

R2 1 Resistor, Chip, 66.5kΩ, 1/10W, 1%, 0603

R3, R4, R5 3 Resistor, Chip, 10kΩ, 1/10W, 1%, 0603

R6, R10, R11 3 Resistor, Chip, 4.02kΩ, 1/10W, 1%, 0603

R7 1 Resistor, Chip, 316kΩ, 1/10W, 1%, 0603

R8 1 Resistor, Chip, 100kΩ, 1/10W, 1%, 0603

R9 1 Resistor, Chip, 10Ω, 1/4W, 1%, 1206

R12 1 Resistor, Chip, 1.00MΩ, 1/10W, 1%, 0603

R13 1 Resistor, Chip, 3.01MΩ, 1/10W, 1%, 0603

R14 1 Resistor, Chip, 10Ω, 1/10W, 5%, 0603

R15 1 Resistor, Chip, 7.5Ω, 1/10W, 5%, 0603

RAC, RSR 2 Resistor, Chip, 0.01Ω, 1/2W, 1%, 1206

Ri 1 Resistor, Chip, 2Ω, 1/2W, 1%, 1210

U1 1 Charger controller, 20 pin VQFN, TI, bq24725RGR

U2 1 Dual digital transistor, 40V, 30mA, SC-74, Rohm, IMD2A

APPLICATION INFORMATION

Negative Output Voltage Protection

Reversely insert the battery pack into the charger output during production or hard shorts on battery to ground

will generate negative output voltage on SRP and SRN pin. IC internal electrostatic-discharge (ESD) diodes from

GND pin to SRP or SRN pins and two anti-parallel (AP) diodes between SRP and SRN pins can be forward

biased and negative current can pass through the ESD diodes and AP diodes when output has negative voltage.

Insert two resistors for SRP and SRN pins to limit the negative current level when output has negative voltage.

Suggest resistor value is 10Ω for SRP pin and 7-8Ω for SRN pin. After adding small resistors, the suggested pre-

charge current is at least 192mA for a 10mΩ current sensing resistor.

Reverse Input Voltage Protection

Q6, R12 and R13 in Figure 1 gives system and IC protection from reversed adapter voltage. In normal operation,

Q6 is turned off by negative Vgs. When adapter voltage is reversed, Q6 Vgs is positive. As a result, Q6 turns on

to short gate and source of Q2 so that Q2 is off. Q2 body diode blocks negative voltage to system. However,

CMSRC and ACDRV pins need R10 and R11 to limit the current due to the ESD diode of these pins when turned

on. Q6 must has low Vgs threshold voltage and low Qgs gate charge so it turns on before Q2 turns on. R10 and

R11 must have enough power rating for the power dissipation when the ESD diode is on. In Figure 2, the

Schottky diode D3 gives the reverse adapter voltage protection, no extra small MOSFET and resistors are

needed.

Reduce Battery Quiescent Current

When the adapter is not present, if VCC is powered with voltage higher than UVLO directly or indirectly (such as

through a LDO or switching converter) from battery, the internal BATFET charge pump gives the BATFET pin 6V

higher voltage than the SRN pin to drive the n-channel BATFET. As a result, the battery has higher quiescent

current. This is only necessary when the battery powers the system due to a high system current that goes

through the MOSFET channel instead of the body diode to reduce conduction loss and extend the battery

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