ISL9216IRZ datasheet(22/34 Pages) RENESAS

22 / 34 page

ISL9216, ISL9217

FN6488 Rev 1.00

Page 22 of 34

November 2, 2007

OVERCURRENT SAFETY FUNCTIONS

The ISL9216 continually monitors the discharge current by

monitoring the voltage at the CSENSE and DSENSE pins. If

that voltage exceeds a selected value for a time exceeding a

selected delay, then the device enters an overcurrent or short

circuit protection mode. In these modes, the ISL9216

automatically turns off both power FETs and hence prevents

current from flowing through the terminals P+ and P-.

The voltage thresholds and the response times of the

overcurrent protection circuits are selectable for discharge

overcurrent, charge overcurrent, and discharge short circuit

conditions. The specific settings are determined by bits in the

“DISCHARGE SET CONFIGURATION REGISTER (ADDR:

05H)” on page 18, and “CHARGE/TIME SCALE

CONFIGURATION REGISTER (ADDR: 06H)” on page 19.

(See also “REGISTERS” on page 14).

In an overcurrent condition, the ISL9216 automatically turns off

the voltage on CFET and DFET pins. The DFET output drives the

discharge FET gate low, turning off the FET quickly. The CFET

output turns off and allows the gate of the charge FET to be pulled

low through a resistor.

By turning off the FETs the ISL9216 prevents damage to the

battery pack caused by excessive current into or out of the cells

(as in the case of a faulty charger or short circuit condition).

When the ISL9216 detects a discharge overcurrent condition, the

ISL9216 turns off both power FETs and sets the DOC bit. (When

the FETs are turned off, the DFET and CFET bits are also reset).

The automatic response to overcurrent during discharge is

prevented by setting the DENOCD bit to “1”. The external

microcontroller can turn on the FETs at any time to recover from

this condition, but it would usually turn on the load monitor

function (by setting the LDMONEN bit) and monitor the LDFAIL bit

to detect that the overcurrent condition has been removed.

When the ISL9216 detects a discharge short circuit condition,

both power FETs are turned off and DSC bit is set. (When the

FETs are turned off, the DFET and CFET bits are also reset). The

automatic response to short circuit during discharge is prevented

by setting the DENSCD bit to “1”. The external microcontroller can

turn on the FETs at any time to recover from this condition, but it

would usually turn on the load monitor function (by setting the

LDMONEN bit) and monitor the LDFAIL bit to detect that the

overcurrent condition has been removed.

When the ISL9216 detects a charge overcurrent condition, both

power FETs are turned off and COC bit is set. (When the FETs

are turned off, the DFET and CFET bits are also reset). The

automatic response to overcurrent during discharge is prevented

by setting the DENOCC bit to “1”. The external microcontroller

can turn on the FETs at any time to recover from this condition,

but it would usually wait to do this until the cell voltages are not

over charged and that the overcurrent condition has been

removed. Or, the microcontroller could wait until the pack is

removed from the charger and then re-attached.

An alternative method of providing the protection function, if

desired by the designer, is to turn off the automatic safety

response. In this case, the ISL9216 device still monitors the

conditions and sets the status bits, but takes no action in

overcurrent or short circuit conditions. Safety of the pack

depends, instead, on the microcontroller to send commands to

the ISL9216 to turn off the FETs.

To facilitate a microcontroller response to an overcurrent

condition, especially if the microcontroller is in a low power state,

a charge overcurrent flag (COC), a discharge overcurrent flag

(DOC), or the short circuit flag (DSC) being set causes the

ISL9216 TEMP3V output to turn on and pull high. (See Figure 5).

This output can be used as an external interrupt by the

microcontroller to wake-up quickly to handle the overcurrent

condition.

LOAD MONITORING

The load monitor function in the ISL9216 (see Figure 4) is used

primarily to detect that the load has been removed following an

overcurrent or short circuit condition during discharge. This can be

used in a control algorithm to prevent the FETs from turning on

while the overload or short circuit condition remains.

The load monitor can also be used by the microcontroller

algorithms after an undervoltage condition on any cells causes

the FETs to turn off. Use of the load monitor prevents the FETs

from turning on while the load is still present. This minimizes

the possible “oscillations” that can occur when a load is applied

in a low capacity pack. It can also be part of a system

protection mechanism to prevent the load from turning on

automatically - i.e. some action must be taken before the pack

is again turned on.

The load monitor circuit can be turned on or off by the

microcontroller. It is normally turned off to minimize current

FIGURE 4. LOAD MONITOR CIRCUIT

VSS

LDMONEN

VMON

VREF

LDFAIL

ISL9216

P-

=1 if VMON > VVMONH

=0 if VMON

VVMONL

VSS

P+

OPEN

DFET

36V

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