ISL9208EVAL2Z Intersil, ISL9208EVAL2Z Datasheet - Page 19

• Manufacturer Part Number: ISL9208EVAL2Z
• Description: EVAL BOARD 2 FOR ISL9208
• Manufacturer: Intersil

Specifications of ISL9208EVAL2Z

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LOAD MONITORING
The load monitor function in the ISL9208 (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
consumption. It must be activated by the external
microcontroller for it to operate. The circuit works by
internally connecting the VMON pin to VSS through a
resistor. The circuit operates shown as in Figure 4.
In a typical pack operation, when an overcurrent or short
circuit event happens, the DFET turns off, opening the
battery circuit to the load. At this time, the R
the load monitor is initially off. In this condition, the voltage at
VMON rises to nearly the pack voltage.
Once the power FETs turn off, the microcontroller activates
the load monitor by setting the LDMONEN bit. This turns on
an internal FET that adds a pull down resistor to the load
monitor circuit. While still in the overload condition the
LDFAIL
= 1 if VMON >V
= 0 if VMON
VSS
ISL9208
LDMONEN
FIGURE 4. LOAD MONITOR CIRCUIT
≤ V
VMONH
VMONL
OPEN
V
REF
POWER FETs
VSS
19
VMON
L
is small and
R
1
R
L
P+
P-
ISL9208
combination of the load resistor, an external adjustment
resistor (R
voltage divider. R
released to a sufficient level, the LDFAIL condition is reset.
OVER-TEMPERATURE SAFETY FUNCTIONS
External Temperature Monitoring
The external temperature is monitored by using a voltage
divider consisting of a fixed resistor and a thermistor. This
divider is powered by the ISL9208 TEMP3V output. This
output is normally controlled so it is on for only short periods
to minimize current consumption.
Without microcontroller intervention, and in the default state,
the ISL9208 provides an automatic temperature scan. This
scan circuit repeatedly turns on TEMP3V output (and the
external temperature monitor) for 5ms out of every 640ms.
In this way, the external temperature is monitored even if the
microcontroller is asleep.
When the TEMP3V output turns on, the ISL9208 waits 1ms
for the temperature reading to stabilize, then compares the
external temperature voltage with an internal voltage divider
that is set to TEMP3V/13. When the thermistor voltage is
below the reference threshold after the delay, an external
temperature fail condition exists. To set the external over-
temperature limit, set the value of R
the resistance of the thermistor at the over-temp threshold.
The TEMP3V output pin also turns on when the
microcontroller sets the AO3:AO0 bits to select that the
external temperature voltage. This causes the TEMPI
voltage to be placed on AO and activates (after 1ms) the
over-temperature detection. As long as the AO3:AO0 bits
point to the external temperature, the TEMP3V output
remains on.
Because of the manual scan of the temperature, it may be
desired to turn off the automatic scan, although they can be
used at the same time without interference. To turn off the
automatic scan, set the ATMPOFF bit.
The microcontroller can over-ride both the automatic
temperature scan and the microcontroller controlled
temperature scan by setting the TEMP3ON configuration bit.
This turns on the TEMP3V output to keep the temperature
control voltage on all the time, for a continuous monitoring of
an over-temperature condition. This likely will consume a
significant amount of current, so this feature is usually used
for special or test purposes.
Protection
As a default, when the ISL9208 detects an internal or
external over-temperature condition, the FETs are turned off,
the cell balancing function is disabled, and the IOT bit or
XOT bit (respectively) is set.
1
), and the internal load monitor resistor form a
1
is chosen so that when the load is
X
resistor to the 12 times
November 2, 2007
FN6446.1