MP3378E

– 4-CHANNEL WLED CONTROLLER WITH BUCK CONVERTER

MP3378E Rev. 1.02

www.MonolithicPower.com

16

5/26/2017

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Floating Driver and Bootstrap Charging

The floating power MOSFET driver is powered

by an external bootstrap capacitor. This floating

driver has its own UVLO protection. The UVLO

rising threshold is 2.2V with a hysteresis of

150mV. The bootstrap capacitor voltage is

regulated internally by VIN2 through DB, R6,

C7, L2, and C5 (see Figure 3). If VIN2-VSW is

more than 5V, then U1 will regulate MB to

maintain a 5V BST voltage across C7.

5V

U1

BST

R6

C7

L2

SW

C5

Figure 3: Internal Bootstrap Charging Circuit

Start-Up and Shutdown

If VIN2 is higher than its appropriate thresholds,

the buck converter starts up. The reference

block starts first, generating stable reference

voltages 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 buck converter:

EN2 low, VIN2 UVLO, and thermal shutdown.

During the shutdown procedure, 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.