CS8312
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4
CIRCUIT DESCRIPTION
Flag Function (See Figure 2)
The flag indicates when the voltage across the two sense
pins is approaching a current limit level that has been
determined by the value of the external sense resistor
(R
SENSE
) and the state of the CTRL and CLI pins. If the
voltage across the sense pins (SENSE+, SENSE–) is less
than the flag turn–on voltage, then the FLAG is off. When
the voltage between the sense pins equals the FLAG turn on
voltage, the FLAG will latch on until the CTRL pin goes
low. FLAG is disabled whenever CTRL is low. Changing the
CLI pin from low to high will increase nominal FLAG turn
on voltage by approximately 45%.
Table 1. FLAG Timing Sequence
State CONTROL SENSE+ FLAG
0 Low X OFF
1 High Below Threshold OFF
2 High Above Threshold ON
3 High X ON
0 Low X OFF
Output Stage
The CS8312 output (OUT) saturates and supplies voltage
to the IGBT (or MOSFET) gate once the CTRL switches
from low to high. As current through the IGBT (MOSFET)
increases and the voltage across the sense resistor passes the
flag turn on voltage, the FLAG will turn on. If the current
through the sense resistor continues to rise and the sense
resistor voltage reaches the regulation sense voltage, then
the gate voltage will fall to a level that regulates the driver
and maintains the regulation sense voltage at the sense
resistor.
Current Limit Function
Changing the CLI pin from a logic low to a logic high
increases the FLAG turn on voltage by approximately 45%
and the regulation sense voltage by approximately 39%
respectively.
Figure 2. Application and Test Diagram
FLAG
CTRL
CLI
OUT
SENSE+
SENSE–
GND
V
CC
CS8312
Microprocessor
V
CC
R
V
CC
V
BAT
LOAD
R
SENSE
0.1 µF
