Datasheet

MAX1533A/MAX1537A
High-Efficiency, 5x Output, Main Power-Supply
Controllers for Notebook Computers
______________________________________________________________________________________ 25
Power-Good Output (PGOOD)
PGOOD is the open-drain output of a comparator that
continuously monitors both SMPS output voltages for
undervoltage conditions. PGOOD is actively held low in
shutdown (SHDN or ON3 or ON5 = GND), soft-start,
and soft-shutdown. Once the digital soft-start termi-
nates, PGOOD becomes high impedance as long as
both outputs are above 90% of the nominal regulation
voltage set by FB_. PGOOD goes low once either
SMPS output drops 10% below its nominal regulation
point, an output overvoltage fault occurs, or either
SMPS controller is shut down. For a logic-level PGOOD
output voltage, connect an external pullup resistor
between PGOOD and V
CC
. A 100kΩ pullup resistor
works well in most applications.
PGOOD is independent of the fault protection states
OVP and UVP.
Fault Protection
Output Overvoltage Protection (OVP)
If the output voltage of either SMPS rises above 111%
of its nominal regulation voltage and the OVP protection
is enabled (OVP = GND), the controller sets the fault
latch, pulls PGOOD low, shuts down both SMPS con-
trollers, and immediately pulls DH_ low and forces DL_
MAX1533A
MAX1537A
LDO5
BST
DH
LX
(R
BST
)*
(C
NL
)*
D
BST
C
BST
C
BYP
INPUT (V
IN
)
N
H
L
LDO5
DL
GND
N
L
(R
BST
)* OPTIONAL—THE RESISTOR LOWERS EMI BY DECREASING
THE SWITCHING-NODE RISE TIME.
(C
NL
)* OPTIONAL—THE CAPACITOR REDUCES LX TO DL CAPACITIVE
COUPLING THAT CAN CAUSE SHOOT-THROUGH CURRENTS.
Figure 6. Optional Gate-Driver Circuitry
POR
ENABLE OVP
ENABLE UVP
BLANK
(POWER-UP)
POWER-
GOOD
FAULT
0.9 x
INT REF_
0.7 x
INT REF_
1.11 x
INT REF_
FAULT
LATCH
TIMER
POWER-GOOD
FAULT
PROTECTION
INTERNAL FB
Figure 7. Power-Good and Fault Protection