MAX1540A Datasheet, PDF (31/49 Pages) Maxim Integrated Products – Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear Regulator

Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
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 (ON_) section) of both
outputs. When the output voltage drops to 0.3V, the dri-
ver 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 MAX1540A/MAX1541 feature a thermal fault-pro-
tection 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 MAX1540A/MAX1541s’ Dual Mode operation
allows the selection of common voltages without requir-
ing external components (Figure 10). For the main con-
troller (OUT1) of the MAX1540A, 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 MAX1540A,
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.
Table 7. Fault Protection and Shutdown Setting Truth Table
OVP/UVP
ON_ DISCHARGE*
UVP PROTECTION
OVP PROTECTION
THERMAL PROTECTION
Yes. Output discharged
V_CC
through a 10Ω resistor,
Yes. UVP fault activates Yes. DH pulled low and DL Yes. Thermal fault activates
and DL forced high when the discharge sequence. forced high immediately. the discharge sequence.
output drops below 0.3V.
Open
REF
Yes. Output discharged
through a 10Ω resistor,
and DL forced high when
output drops below 0.3V.
No. DL forced low when
shut down.
No. UVP disabled.
Yes. DH pulled low and DL Yes. Thermal fault activates
forced high immediately. the discharge sequence.
Yes. UVP fault activates _{No. OVP disabled.}
the discharge sequence.
Yes. Thermal fault activates
the discharge sequence.
GND
No. DL forced low when
shut down.
No. UVP disabled.
*Discharge-mode state latched on power-up.
No. OVP disabled.
Yes. Thermal fault activates
the discharge sequence.
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