ADP3419 查看數據表（PDF） - Analog Devices
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ADP3419 Datasheet PDF : 16 Pages
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ADP3419
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
(tpdlDRVH) following the falling edge of the input signal. When Q1
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
with tSW(TO) delay. If Q1 is still turned on, that is, its drain is
shorted to the source, Q2 turns on and creates a direct short
circuit across the VDCIN voltage rail. The crowbar action causes
the fuse in the VDCIN current path to open. The opening of the
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
HH
HH
L
L
L
HH
LL
H
L
L
HL
HH
L
L
L
HL
LL
L
L
L
L*
*L
L
L
H
**
*L
L
H
L
**
*L
H
H
H
**
*L
H
* = Don’t Care.
Rev. A | Page 10 of 16
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