MP2235S datasheet(13/19 Pages) MPS

13 / 19 page

MP2235S –3 A, 16 V, 800 kHz SYNCHRONOUS STEP-DOWN CONVERTER

MP2235S Rev.1.0

www.MonolithicPower.com

4/15/2015

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

Thermal Shutdown

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures.

When the die temperature exceeds 150°C, the

entire chip shuts down. 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. This

UVLO’s rising threshold is 2.2 V with a

hysteresis of

150 mV. The bootstrap capacitor

voltage is regulated internally by VIN through D1,

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

VSW exceeds 5 V, U1 regulates M1 to maintain

a 5 V BST voltage across C4. A 20 Ω resistor

placed between the SW and BST capacitors is

strongly recommended 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, and 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 signal 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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