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

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

CS8312

Microprocessor

R

LOAD

0.1

µF