MP6005

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

MP6005 Rev. 1.0

www.MonolithicPower.com

21

2/5/2021

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GND

VCC

NA

RVCC DVCC

CVCC

Figure 8: Flyback VCC from NA Winding

The auxiliary winding supply voltage can be

calculated with Equation (5):

DVCCF

DOF

OUT

S

A

CC

V

-

)

V

+

(V

x

N

N

=

V

(5)

Where VDVCCF is the DVCC diode voltage drop

from the auxiliary winding.

In forward mode, it is recommended to have the

VCC capacitor be less than 4.7µF. VCC can

also be powered by the auxiliary winding

transformer. Figure 9 shows VCC from the NA

winding in forward mode.

GND

VCC

NA

DVCC

CVCC

LVCC

Figure 9: Forward VCC from NA Winding

The auxiliary winding supply voltage can be

calculated with Equation (6):

OUT

S

A

CC

x V

N

N

=

V

(6)

VCC should be less than 16V.

Setting Output Voltage (VOUT) Compensation

and Frequency Dithering

The SENSE pin sets the output voltage (VOUT)

compensation and frequency dithering functions.

After turning on, the MP6005 outputs a 100µA

current to the SENSE pin to detect the SENSE

resistance.

Based

on

the

resistance,

the

MP6005 determines the compensation and

frequency dithering type. See Table 2 on page

17 for SENSE programming options.

The VOUT compensation function only works in

PSR mode.

Setting the Current-Sense (CS) Resistor

The external MOSFET current is sensed by a

sensing resistor. If VSENSE exceeds the current-

limit threshold (typically 160mV), the MP6005

turns off the GATE output for the cycle.

To avoid exceeding the current limit, the voltage

across the sense resistor (RSENSE) should be

less than 80% of the current limit voltage

(160mV).

RSENSE

can

be

estimated

with

Equation (7):

PEAK

mV

SENSE

I

160

x

0.8

=

R

(7)

Where IPEAK is the primary-side peak current.

Selecting a Power MOSFET

The MP6005 drives a wide variety of N-channel

MOSFETs. The critical parameters of selecting

a MOSFET are the maximum drain-to-source

voltage (VDS(MAX)), maximum current (ID(MAX)), on

resistance (RDS(ON)), total gate charge (QG), and

turn-on threshold (VTH).

In flyback mode, the off-state voltage can be

calculated with Equation (8):

MOSFET

IN

OUT

V

= V +N V



(8)

To avoid a voltage spike when the power

MOSFET turns off, VDS(MAX) should exceed 1.5

times the VMOSFET.

In forward mode, the off-state voltage across

the MOSFET can be calculated with Equation

(9):

IN

N

I

MOSFET

V

+

D

-

1

x V

D

=

V

(9)

Where D is the duty cycle with a 70% maximum

duty cycle limit.

The maximum current through the power

MOSFET occurs once VIN is at its minimum and

the output power is at its maximum. The current

rating should exceed 1.5 times IRMS.

The MOSFET

’s on resistance determines the

conduction loss. To reduce conduction loss, the

on resistance should be as low as possible. QG

is important for MOSFET selection since it

determines the commutation time. A high QG