MP6903 datasheet(9/10 Pages) MPS

9 / 10 page

MP6903- FAST TURN-OFF INTELLIGENT CONTROLLER

MP6903 Rev. 1.04

www.MonolithicPower.com

1/31/2013

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

Light-Load Latch-Off Function

The gate driver of MP6903 is latched to save the

driver loss at light-load condition to improve

efficiency. See Figure5, when the synchronous

MOSFET’s conducting period keeps lower than

light load timing (TLL) for longer than the light-

load-enter delay (TLL-Delay), MP6903 enters light-

load mode and latches off the gate driver. Here

the synchronous MOSFET’s conducting period is

from turn on of the gate driver to the moment

when VGS drops to below 1V (VLL_GS).

Secondary Side Current

Normal Mode

Light Load Mode

tLL

TLL-dELAY

Figure 5: MP6903 Enters Light Load Mode

During light-load mode, MP6903 monitors the

synchronous MOSFET’s body diode conducting

period by sensing the time duration of the VDS

below -250mV(VLL_DS). If it is longer than TLL+TLL-

H (TLL-H, light-load-enter pulse width hysteresis),

the light-load mode is finished and gate driver of

MP6903 is unlatched to restart the synchronous

rectification, see Figure6.

For MP6903, the light load enter timing (TLL) is

programmable by connecting a resistor (RLL) on

LL pin, by monitoring the LL pin current (the LL

pin voltage keeps at ~2V internally), TLL is set as

following (a 1nF capacitor is recommended to

decouple the noise on this pin):

2.2us

TR (k )

100k

 



Figure 6: MP6903 Exits Light Load Mode

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