MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER

MPQ28261 Rev. 1.12

www.MonolithicPower.com

14

10/10/2013

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When the silicon die temperature exceeds

150°C, the whole chip shuts down: The HS-FET

and LS-FET turn off, and the SS pin voltage

goes low. When the temperature drops below

the lower threshold—typically 140°C—the chip

restarts with an SS.

Floating Driver and Bootstrap Charging

The floating power MOSFET driver has several

features to ensure stability and functionality,

such as its own UVLO protection with a rising

threshold of 2.2V and a hysteresis of 150mV.

An external bootstrap capacitor—regulated

(see

Figure

4)—powers

this

driver.

U1

regulates M1 to maintain a 5V BST voltage

D1

M1

BST

C4

L1

SW

U1

5V

C2

Figure 4: Internal Bootstrap Charging Circuit

Startup and Shutdown

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 a stable power

supply for the rest of the device.

Three events can shut down the chip: EN low,

the signaling path shuts down first to avoid

triggering any faults. Then the COMP voltage

and the internal supply rail are pulled down.

The floating driver is not subject to this

shutdown command.