ADP3211 ON Semiconductor, ADP3211 Datasheet - Page 17

• Manufacturer Part Number: ADP3211
• Description: 7-bit, Programmable, Single-phase, Synchronous Buck Controller
• Manufacturer: ON Semiconductor

Output Crowbar
the DRVL output is driven high (turning the low−side
MOSFETs on) and DRVH is driven low (turning the
high−side MOSFETs off) when the output voltage exceeds
the CPU or GMCH OVP threshold.
capacitor to discharge and the current to reverse due to
current build up in the inductors. If the output overvoltage
is due to a drain−source short of the high−side MOSFET,
turning on the low−side MOSFET results in a crowbar
across the input voltage rail. The crowbar action blows the
fuse of the input rail, breaking the circuit and thus
protecting the CPU or GMCH chip−set from destruction.
latched off. The latchoff function can be reset by removing
and reapplying V
the EN pin low.
To protect the load and output components of the supply,
Turning on the low−side MOSFETs forces the output
When the OVP feature is triggered, the ADP3211 is
Figure 31. Single−Phase Waveforms in DCM with
Inductor
Current
Voltage
Figure 30. Inductor Current and Switch Node in
Switch
Node
t
0
CSREF to CSCOMP 50mV/div
SWITCH NODE
t
1
5.0 V/div
CC
1 A Load Current
to the ADP3211 or by briefly pulling
LOW SIDE GATE 5V/div
4 ms/div
DCM
t
2
t
3
t
4
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17
Reverse Voltage Protection
negative V
and other output components. The ADP3211 provides a
reverse voltage protection (RVP) function without
additional system cost. The V
through the CSREF pin. When the CSREF pin voltage
drops to less than −300 mV, the ADP3211 triggers the RVP
function by setting both DRVH and DRVL low, thus
turning off all MOSFETs. The reverse inductor currents can
be quickly reset to 0 by discharging the built−up energy in
the inductor into the input dc voltage source via the
forward−biased body diode of the high−side MOSFETs.
The RVP function is terminated when the CSREF pin
voltage returns to greater than −100 mV.
negative V
MOSFETs results in a very large reverse inductor current.
To prevent damage to the chip−set caused from negative
voltage, the ADP3211 maintains its RVP monitoring
function even after OVP latchoff. During OVP latchoff, if
the CSREF pin voltage drops to less than −300 mV, the
low−side MOSFETs is turned off by setting DRVL low.
DRVL will be set high again when the CSREF voltage
recovers to greater than −100 mV.
of the ADP3211. The CSREF pin is disconnected from the
output voltage and pulled negative. As the CSREF pin
drops to less than −300 mV, the low−side and high−side
FETs turn off.
Output Enable and UVLO
voltage to the controller must be greater than the V
threshold and the EN pin must be driven high. If the V
voltage is less than the V
is logic low, the ADP3211 shuts off. In shutdown mode, the
controller holds DRVH and DRVL low and drives PWRGD
to low.
sequencing during startup and shutdown of the ADP3211.
All input pins must be at ground prior to removing or
applying V
impedance state while V
Very large reverse current in inductors can cause
Sometimes the crowbar feature inadvertently results in
Figure 32 shows the reverse voltage protection function
For the ADP3211 to begin switching, the V
The user must adhere to proper power−supply
CCGFX
CCGFX
Figure 32. ADP3211 RVP Function
CC
5.0 V/div
PWRGD
, and all output pins should be left in high
OVP RVP
voltage, which is harmful to the chip−set
voltage because turning on the low−side
CC
OUTPUT VOLTAGE
CCUVLO
LOW SIDE GATE
is off.
SWITCH NODE
CCGFX
0.5 V/div
5.0 V/div
10 V/div
threshold or the EN pin
20 ms/div
voltage is monitored
CC
supply
CCOK
CC