ADP3419

Rev. A | Page 10 of 16

LOW-SIDE DRIVER SHUTDOWN

The low-side driver shutdown DRVLSD allows a control signal

to shut down the synchronous rectifier. Under light load

conditions, DRVLSD should be pulled low before the polarity

reversal of the inductor current to maximize light load

conversion efficiency. DRVLSD can also be pulled low for

reverse voltage protection purposes.

When DRVLSD is low, the low-side driver stays low. When

DRVLSD is high, the low-side driver is enabled and controlled

by the driver signals, as previously described.

LOW-SIDE DRIVER TIMEOUT

In normal operation, the DRVH signal tracks the IN signal and

turns off the Q1 high-side switch with a few 10 ns delay

is turned off, DRVL is allowed to go high, Q2 turns on, and the

SW node voltage collapses to zero. But in a fault condition such

as a high-side Q1 switch drain-source short circuit, the SW

node cannot fall to zero, even when DRVH goes low. The

ADP3419 has a timer circuit to address this scenario. Every

time the IN goes low, a DRVL on-time delay timer is triggered.

If the SW node voltage does not trigger a low-side turn-on, the

DRVL on-time delay circuit does it instead, when it times out

shorted to the source, Q2 turns on and creates a direct short

fuse saves the load (CPU) from potential damage that the high-

side switch short circuit could have caused.

CROWBAR FUNCTION

In addition to the internal low-side drive time-out circuit, the

ADP3419 includes a CROWBAR input pin to provide a means

for additional overvoltage protection. When CROWBAR goes

high, the ADP3419 turns off DRVH and turns on DRVL. The

crowbar logic overrides the overlap protection circuit, the

shutdown logic, the DRVLSD logic, and the UVLO protection

on DRVL. Thus, the crowbar function maximizes the overvolt-

age protection coverage in the application. The CROWBAR can

be either driven by the CLAMP pin of buck controllers, such as

the ADP3422, ADP3203, ADP3204, or ADP3205, or controlled

by an independent overvoltage monitoring circuit.

Table 4. ADP3419 Truth Table

CROWBAR

UVLO

SD

DRVLSD

IN

DRVH

DRVL

L

L

H

H

H

H

L

L

L

H

H

L

L

H

L

L

H

L

H

H

L

L

L

H

L

L

L

L

L

L

L

*

*

L

L

L

H

*

*

*

L

L

H

L

*

*

*

L

H

H

H

*

*

*

L

H

* = Don’t Care.