MAX1924V Просмотр технического описания (PDF) - Maxim Integrated

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MAX1924V

Advanced Li+ Battery-Pack Protectors

Maxim Integrated 

Advanced Li+ Battery-Pack Protectors

NORMAL OPERATION

OC FAULT

NO

VRSENSE < VOC_TH

FOR 3ms

YES

TKO, CGO = H

NORMAL OPERATION

OD FAULT

NO

VRSENSE > VOD_TH

FOR 3ms

YES

DSO, TKO, CGO = H

NO

VB4P > VSRC + 0.1V

YES

NO

VSRC > VB4P + 0.1V

YES

Figure 5. Charge-Current Fault

Set the nominal values of the trickle charge current by

selecting resistor RTKO based on the following equation:

RTKO = (VCHRG - VPACK)/ITKO

where VCHRG is the charger output voltage, VPACK is

the battery-pack voltage, and ITKO is the trickle-charge

current.

When the trickle-charge option is not used, float CGO

and connect TKO to the gate of the overcharge protec-

tion MOSFET (see Figure 9). When a charger is applied

and the voltage on one or more cells is less than

VUV_TH, the MAX1894/MAX1924 modulate the TKO out-

put until all cells exceed VUV_TH.

Protection FET Drivers

All three external MOSFETs have their source pins con-

nected to the SRC pin. When a MOSFET is turned off, FET

drivers pull the gate to the SRC voltage. Additional exter-

nal pullup resistors are not needed. When the MOSFET is

turned on, the VGS is limited to -14V by a clamp circuit

built in the drivers. This allows use of MOSFETs with maxi-

mum VGS of -20V. All three drivers have the same circuit-

ry and drive capability. The quiescent current in normal

operation is less than 3µA per driver.

Figure 6. Discharge-Current Fault

RSENSE Selection

All current faults are detected using a current-sense

resistor connected between BN and PKN. The value of

this resistor sets the fault current levels. Charge-current

fault is given by:

IOC_ TH

=

VOC_ TH

RSENSE

=

100mV

RSENSE

Discharge-current fault is given by:

IOD_ TH

=

VOC_ TH

RSENSE

=

145mV

RSENSE

Pack-short current fault is given by:

IPS_ TH

=

VPS_ TH

RSENSE

=

405mV

RSENSE

Select RSENSE to obtain the desired fault current levels.

For example, a 20mΩ RSENSE sets the charge current

fault at 5A. Choose an RSENSE that can withstand the

dissipation during normal operation and current fault

conditions. For example, pack-short current is given by:

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