MP1475S datasheet(13/19 Pages) MPS

13 / 19 page

MP1475S – HIGH-EFFICIENCY, 3A, 16V, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER

MP1475S Rev. 1.0

www.MonolithicPower.com

1/8/2015

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

Over-Current Protection (OCP) and Hiccup

The MP1475S has a cycle-by-cycle over-

current limit when the inductor current peak

value exceeds the set current-limit threshold.

Meanwhile, the output voltage drops until VFB is

below the under-voltage (UV) threshold (50%

below the reference, typically). Once UV is

triggered, the MP1475S enters hiccup mode to

re-start the part periodically. This protection

mode is useful when the output is dead-shorted

to ground and greatly reduces the average

short-circuit current to alleviate thermal issues

and protect the regulator. The MP1475S exits

hiccup mode once the over-current condition is

removed.

Thermal Shutdown (TSD)

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures.

When the die temperature exceeds 150°C, it

shuts down the whole chip. When the

temperature drops below its lower threshold

(130°C, typically), 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. The

UVLO’s rising threshold is 2.2V with a

hysteresis of 150mV. The bootstrap capacitor

voltage is regulated internally by VIN through D1,

M1, R3, C4, L1, and C2 (see Figure 6). If (VIN-

VSW) exceeds 5V, U1 regulates M1 to maintain

BST

voltage

across

C4.

recommended strongly to place a 20Ω resistor

between the SW and BST cap to reduce SW

spike voltage.

VIN

BST

VOUT

Figure 6. Internal Bootstrap Charging Circuit

Start-Up and Shutdown

If both VIN and VEN exceed their respective

thresholds, the chip starts up. The reference

block starts first, generating stable reference

voltage and currents, then the internal regulator

is enabled. The regulator provides a stable

supply for the remaining circuitries.

Three events can shut down the chip: VEN low,

VIN low, and thermal shutdown. During the

shutdown procedure, the signaling path is

blocked first 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.

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