CURRENT COMPARATOR AND PWM LATCH (see fig.7):

The current comparator senses the voltage across the current sense resistor (Rs) and, by comparing it

with the programming signal delivered by the multiplier, determines the exact time when the external

MOSFET is to be switched off. The PWM latch avoids spurious switchings of the MOSFET which might

result from the noise generated.

The output of the multiplier is internally clamped to 1.7V, (typ.) thus current limiting occurs if the voltage

across Rs reaches this value.

DRIVER (see fig.8)

A totem pole buffer, with 400mA source and sink capability, allows driving an external MOSFET. An in-

ternal pull-down circuit holds the output low when the device is in UVLO conditions, to ensure that the

external MOSFET cannot be turned on accidentally.

D97IN676

RS

4

X

Q

DRIVER

R

S

Q

CMP

1.7V

Figure 7. Current Comparator and PWM latch

D97IN675

E/A

4

X

CURR.CMP

23

Rs

1.7V

Figure 6. Multiplier Block.

AN966 APPLICATION NOTE

6/21