MP6910- FAST TURN-OFF INTELLIGENT RECTIFIER

MP6910 Rev. 1.04

www.MonolithicPower.com

4

1/3/2013

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BLOCK DIAGRAM

Logic

Driver

VDD

VD

VSS

Control

Circuitry

Figure 1—Function Block Diagram

OPERATION

The MP6910 supports operation in DCM and

Quasi-Resonant Flyback converters. The control

circuitry controls the gate in forward mode and

will turn the gate off when the MOSFET current is

fairly low.

Blanking

The control circuitry contains a blanking function.

When it pulls the integrate Mosfet on/off, it makes

sure that the on/off state at least lasts for some

time. The turn on blanking time is ~1.6us, which

determines the minimum on-time. During the turn

on blanking period, the turn off threshold is not

totally blanked, but changes the threshold

voltage to ~+50mV (instead of -30mV). This

assures that the part can always be turned off

even during the turn on blanking period. (Albeit

slower)

Under-Voltage Lockout (UVLO)

When the VDD is below UVLO threshold, the part

is in sleep mode and the integrated Mosfet is

never turned on.

Basic Operation

The basic operations of flyback converter with

MP6910 are:

Turn On Phase

The switch current will first flow through the

body diode of the integrate Mosfet, which

generates a negative Vds across it (<-

500mV). The voltage is much smaller than

the turn on threshold of the control circuitry (-

70mV), which turns on the integrate Mosfet

after 200ns turn on delay (defined in Fig.2).

Conducting Phase

When the integrated Mosfet is turned on,

Vds becomes to rise according to its on

resistance, as soon as Vds rises above the

turn on threshold (-70mV), the control

circuitry stops pulling up the gate driver,

which leads the driver voltage of the

integrate Mosfet dropped to larger the on

resistance to ease the rise of Vds. By doing

that, Vds is adjusted to be around -70mV

even when the current through the switch is