MP6005

– WIDE-INPUT, HIGH-EFFICIENCY FLYBACK AND FORWARD CONTROLLER

MP6005 Rev. 1.0

www.MonolithicPower.com

16

2/5/2021

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© 2021 MPS. All Rights Reserved.

MODE to rise to steady state before the

MP6005 detects VMODE.

Pulse-Width Modulation (PWM) Operation

The MP6005 can be set for flyback or forward

topology. In flyback topology, the external N-

channel MOSFET turns on at the beginning of

each cycle and forces the transformer current to

increase. The current through this MOSFET is

sensed after the sum of the SENSE current and

slope compensation exceed VCOMP. After the

current is sensed, the external MOSFET turns

off. The transformer current then transmits

energy from the primary-side winding to the

secondary-side winding, and charges the output

capacitor through the Schottky diode. The

transformer

’s primary-side current is controlled

by VCOMP, which is controlled by the output

feedback voltage. Therefore, the output voltage

controls the transformer current to satisfy the

load. In forward topology, energy is transferred

from

the

primary-side

to

secondary-side

winding

while

the

primary-side

N-channel

MOSFET is on. The primary-side peak current

is controlled by VCOMP, which is controlled by an

external

TL431

regulator

and

optocoupler

feedback.

See the Voltage Control section below for

details on output voltage feedback.

Voltage Control

PSR Mode

Unlike

traditional

flyback

with

optoisolator

feedback, the MP6005 can detect the feedback

(FB)

pin’s auxiliary winding voltage during the

secondary-side output diode conduction period.

Assume the secondary winding acts as the

master, and the auxiliary winding acts as the

slave. When the secondary-side diode conducts,

the feedback voltage can be calculated with

Equation (1):

FBL

FBH

FBL

DOF

OUT

S

A

FB

R

+

R

R

x

)

V

+

(V

x

N

N

=

V

(1)

Where VDOF is the output diode forward-drop

voltage, VOUT is the output voltage, NA is the

auxiliary winding turn, NS is the secondary-side

output winding, and RFBH and RFBL are the

resistor dividers for feedback sampling.

Figure 2 shows feedback sample control in

discontinuous conduction mode (DCM).

VIN

IPEAK

VFB

FB Sample

VSW

tCON

FB Sample

>0.7µs

IPRI

ISEC

Blanking

Time

Blanking

Time

Figure 2: Discontinuous Conduction Mode (DCM)

Condition Feedback Sample Control

Figure 3 shows feedback sample control in

continuous conduction mode (CCM).

Next clock

IPRI

ISEC

VIN

FB Sample

VFB

Vsw

tCON

FB Sample

Blanking

Time

Blanking

Time

Figure 3: Continuous Conduction Mode (CCM)

Condition Feedback Sample Control

The

MP6005

regulates

the

primary-side

MOSFET VSENSE current above 36mV and

begins sampling the auxiliary-winding voltage

after the power MOSFET turns off. A 300ns

blanking time is added to avoid spike ringing

due to leakage inductance. To guarantee a

sufficient feedback sample period under light-

load

conditions,

the

output

diode

current

conduction time (tCON) should exceed 600ns

before the diode current drops to 0A in each

cycle.

It

is

recommended

to

design

the

transformer to ensure that tCON exceeds 700ns

when VSENSE_PK = 33mV. The MP6005 GATE

signal also provides a 1.2µs minimum off time,

limited by a 70% max duty cycle, to guarantee

sufficient feedback sample time while the

MP6005 works in a high duty cycle. During the

feedback sense period, the FB pin’s signal is

sent to the negative EA input, and remains

there after the sense window has elapsed. The

EA voltage output (VEA) is generated on the