MP1470B – SYNCHRONOUS, STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
Over-Current Protection and Hiccup Mode
The MP1470B has a cycle-by-cycle over-
current limit for when the inductor current peak
value exceeds the set current limit threshold.
When the output voltage drops to trigger a UV
event (FB falls below the under-voltage (UV)
threshold (typically 140mV)), the MP1470B
enters hiccup mode to restart the part
periodically. This protection mode is especially
useful when the output is dead-shorted to
ground. This greatly reduces the average short-
circuit current to alleviate thermal issues and
protect the regulator. The MP1470B exits
hiccup mode once the over-current condition is
removed.
Figure 3: Internal Bootstrap Charger Start-Up
and Shutdown Circuit
If both VIN and EN exceed their respective
thresholds, the chip starts up. The reference
block starts first, generating a stable reference
voltage and currents, and then the internal
regulator is enabled. The regulator provides a
stable supply for the remaining circuits.
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 falls below its lower threshold
(typically 130°C), the chip is enabled again.
Three events can shut down the chip: EN low,
VIN low, and thermal shutdown. The shutdown
procedure starts by initially blocking the
signaling path 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.
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.
VIN regulates the bootstrap capacitor voltage
internally through D1, M1, R4, C4, L1, and C2
(see Figure 3). If VIN-VSW exceeds 5V, U1
regulates M1 to maintain a 5V BST voltage
across C4.
MP1470B Rev. 1.0
8/25/2015
www.MonolithicPower.com
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