MP1496S – SYNCHRONOUS, STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
Over-Current Protection and Hiccup
The MP1496S has a cycle-by-cycle over-current
limit when the inductor current peak exceeds the
set current-limit threshold. Meanwhile, output
voltage drops until FB falls below the under-
voltage (UV) threshold—typically 50% below the
reference. Once UV triggers, the MP1496S
enters hiccup mode to periodically restart the
part. This protection mode is especially useful
when the output is dead-shorted to ground. This
greatly reduces the average short circuit current,
alleviates thermal issues, and protects the
regulator. The MP1496S exits hiccup mode once
the over current condition is removed.
Figure 3: Internal Bootstrap Startup and Shutdown
Charging Circuit
If both VIN and EN exceed their appropriate
thresholds, the chip starts. The reference block
starts first, generating stable reference voltages
and currents, and then the internal regulator is
enabled. The regulator provides stable supply for
the remaining circuitries.
LS-FET Negative Current Limit Protection
To prevent LS-FET current goes too negative,
The MP1496S will sense the LS-FET
current during LS-FET turn on period. It provides
cycle-by-cycle negative current limit protection
when the inductor valley current is lower than the
set negative current limit. Internal 500kHz or
250kHz (fold-back frequency) clock initiates the
PWM cycle, If LS-FET negative current limit is
triggered before internal clock comes, LS-FET
will turn off and wait for internal clock to turn on
HS-FET. In this case, MP1496S will work at DCM
mode. If LS-FET negative current limit is not
triggered in a clock cycle, MP1496S works at
CCM mode. During soft start period, the LS-FET
negative current limit is gradually decrease from
0A(typical) to -1A (typical).
Three events can shut down the chip: EN low, VIN
low, and thermal shutdown. In shutdown, the
signaling path is first blocked to avoid any fault
triggering. The COMP voltage and the internal
supply rail are then pulled down. The floating
driver is not subject to this shutdown command.
Thermal Shutdown
Thermal shutdown prevents the chip from
operating at exceedingly high temperatures.
When the silicon die temperature exceeds
150°C, the whole chip shuts down. When the
temperature drops below its lower threshold—
typically 130°C—the chip is enabled again.
Floating Driver and Bootstrap Charging
An external bootstrap capacitor powers the
floating power MOSFET driver. This floating
driver has its own UVLO protection with a rising
threshold of 2.2V and a hysteresis of 150mV.
The bootstrap capacitor voltage is regulated
internally by VIN through D1, M1, C4, L1 and C2
(see Figure 3). If (VIN-VSW) exceeds 5V, U1 will
regulate M1 to maintain a 5V BST voltage across
C4. A 10ꢀ resistor placed between SW and BST
cap is strongly recommended to reduce SW
spike voltage.
MP1496S Rev.1.1
3/29/2017
www.MonolithicPower.com
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