Rainbow Electronics MAX1541 - Manual (Page 31)

cannot tolerate a negative voltage, place a power
Schottky diode across the output to act as a reverse-
polarity clamp. If the condition that caused the overvolt-
age persists (such as a shorted high-side MOSFET),
the input fuse blows. The MAX1541 ignores OVP faults
on OUT1 when it detects a transition on GATE
(FBLANK enabled). Toggle ON1 or ON2, or cycle V
CC
power below 1V to clear the fault latch and restart the
controller.
OVP is disabled when OVP/UVP is connected to REF or
GND (Table 7).
Undervoltage Protection (UVP)
When the output voltage drops below 70% of the nomi-
nal regulation voltage and UVP is enabled (OVP/UVP =
V
CC or REF), the controller sets the fault latch and acti-
vates the output discharge sequence (see the
Shutdown and Output Discharge section) of both out-
puts. When the output voltage drops to 0.3V, the driver
pulls DL high so the synchronous rectifier turns on,
clamping the output to GND. UVP is ignored for at least
10ms (min) after startup (ON_ rising edge), and when
transitions are detected on GATE (MAX1541 only,
FBLANK enabled). Toggle ON1 or ON2, or cycle V
CC
power below 1V to clear the fault latch and restart the
controller.
UVP is disabled when OVP/UVP is left open or connect-
ed to GND (Table 7).
Thermal Fault Protection
The MAX1540/MAX1541 feature a thermal fault-protec-
tion circuit. When the linear regulator is disabled
(LDOON = GND), the controller sets the thermal limit at
+160
°C. When the linear regulator is enabled (LDOON
= V CC ), the controller sets the thermal limit at +150 °C to
protect the internal linear regulator from continuous
short-circuit conditions. Once the junction temperature
exceeds the thermal limit, the thermal-protection circuit
activates the fault latch, pulls PGOOD1 and PGOOD2
low, disables the linear regulator, and activates the out-
put discharge sequence of both outputs regardless of
the OVP/UVP setting. Toggle ON1 or ON2, or cycle V
CC
power below 1V to reactivate the controller after the
junction temperature cools by 10
°C.
Output Voltage
Preset Output Voltages
The MAX1540/MAX1541s’ Dual Mode operation allows
the selection of common voltages without requiring
external components (Figure 10). For the main con-
troller (OUT1) of the MAX1540, connect FB1 to GND for
a fixed 1.8V output, to V
CC for a fixed 1.2V output, or
connect FB1 directly to OUT1 for a fixed 0.7V output.
For the secondary controller (OUT2) of the MAX1540,
connect FB2 to GND for a fixed 2.5V output, to V
CC
for
a fixed 1.5V output, or connect FB2 directly to OUT2 for
a fixed 0.7V output. The main controller (OUT1) of the
MAX1541 regulates to the voltage set at REFIN1 (V
FB1
= V REFIN1 ) and does not support Dual Mode operation.
For the secondary controller (OUT2) of the MAX1541,
connect FB2 to GND for a fixed 2.5V output, to V
CC
for
a fixed 1.8V output, or connect FB2 directly to OUT2 for
a fixed 0.7V output. Table 8 shows the output voltage
configuration.
MAX1540/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
______________________________________________________________________________________ 31
Table 7. Fault Protection and Shutdown Setting Truth Table
OVP/UVP ON_ DISCHARGE* UVP PROTECTION OVP PROTECTION THERMAL PROTECTION
V CC
Yes. Output discharged
through a 10
Ω resistor,
and DL forced high when
output drops below 0.3V.
Yes. UVP fault activates
the discharge sequence. Yes. DH pulled low and DL
forced high immediately. Yes. Thermal fault activates
the discharge sequence.
Open
Yes. Output discharged
through a 10
Ω resistor,
and DL forced high when
output drops below 0.3V.
No. UVP disabled.
Yes. DH pulled low and DL
forced high immediately. Yes. Thermal fault activates
the discharge sequence.
REF
No. DL forced low when
shut down. Yes. UVP fault activates
the discharge sequence.
No. OVP disabled.
Yes. Thermal fault activates
the discharge sequence.
GND
No. DL forced low when
shut down.
No. UVP disabled. No. OVP disabled.
Yes. Thermal fault activates
the discharge sequence.
*Discharge-mode state latched on power-up.