Datasheet

MAX15035
15A Step-Down Regulator with Internal Switches
______________________________________________________________________________________ 19
output voltage, connect an external pullup resistor
between PGOOD and V
DD
. A 100kΩ pullup resistor
works well in most applications. Figure 7 shows the
power-good and fault-protection circuitry.
Overvoltage Protection (OVP)
When the internal feedback voltage rises 300mV above
the target voltage and OVP is enabled, the OVP compara-
tor immediately forces LX low, pulls PGOOD low, sets the
fault latch, and disables the SMPS controller. Toggle EN
or cycle V
CC
power below the V
CC
POR to clear the fault
latch and restart the controller.
Undervoltage Protection (UVP)
When the feedback voltage drops 200mV below the
target voltage (REFIN), the controller immediately pulls
PGOOD low and triggers a 200μs one-shot timer. If the
feedback voltage remains below the undervoltage fault
threshold for the entire 200μs, the undervoltage fault
latch is set and the SMPS begins the shutdown
sequence. When the internal target voltage drops
below 0.1V, the MAX15035 forces a high impedance on
LX. Toggle EN or cycle V
CC
power below V
CC
POR to
clear the fault latch and restart the controller.
Thermal-Fault Protection (T
SHDN
)
The MAX15035 features a thermal fault-protection cir-
cuit. When the junction temperature rises above
+160°C, a thermal sensor activates the fault latch, pulls
PGOOD low, shuts down the controller, and forces a
high impedance on LX. Toggle EN or cycle V
CC
power
below V
CC
POR to reactivate the controller after the
junction temperature cools by 15°C.
Quick-PWM Design Procedure
Firmly establish the input voltage range and maximum
load current before choosing a switching frequency and
inductor operating point (ripple-current ratio). The prima-
ry design trade-off lies in choosing a good switching fre-
quency and inductor operating point, and the following
four factors dictate the rest of the design:
• Input Voltage Range: The maximum value
(V
IN(MAX)
) must accommodate the worst-case input
supply voltage. The minimum value (V
IN(MIN)
) must
account for the lowest input voltage after drops due
to connectors, fuses, and battery selector switches. If
there is a choice at all, lower input voltages result in
better efficiency.
• Maximum load current: There are two values to
consider. The peak load current (I
LOAD(MAX)
)
determines the instantaneous component stresses
and filtering requirements, and thus drives output
capacitor selection, inductor saturation rating, and
the design of the current-limit circuit. The continu-
ous load current (I
LOAD
) determines the thermal
stresses and thus drives the selection of input
capacitors, MOSFETs, and other critical heat-con-
tributing components.
OVP ENABLED
POWER-GOOD
FAULT
TARGET
- 200mV
TARGET
+ 300mV
FAULT
LATCH
FB
OVP
SOFT-START
COMPLETE
EN
UVP
ONE-
SHOT
200μs
IN
CLK
OUT
POWER-GOOD AND FAULT PROTECTION
Figure 7. Power-Good and Fault Protection