MPX2003

– UP TO 140kHz ALL-IN-ONE FLYBACK CONTROLLER

MPX2003 Rev. 1.0

MonolithicPower.com

28

8/5/2022

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

© 2022 MPS. All Rights Reserved.

A small capacitor is connected to the CS pin and

RHVCS to form a low-pass filter for noise filtering

when the MOSFET turns on and off (see Figure

17 on page 28).

PDRV

CS

MPX2003

RHVCS

CCS

RSENSE

Low-Pass Filter

Figure 17: Low-Pass Filter on CS

The low-

pass filter’s R x C constant should not

exceed 1/3 of the leading-edge blanking period

for SCP (tLEB-S, typically 250ns). Otherwise, the

filtered sensed voltage cannot reach the SCP

point to trigger SCP if an output short circuit

occurs.

Ramp Compensation

When

adopting

peak

current

control,

subharmonic oscillations occur when the duty

cycle exceeds 50% (D > 0.5) in CCM. The

MPX2003 provides internal ramp compensation

to solve this issue. Use the coefficient α to

determine whether the ramp compensation is

appropriate. α can be calculated with Equation

(15):











MAX

IN(MIN)

SENSE

RAMP

MAX

M

IN(MIN)

SENSE

RAMP

M

DV

R

- S

(1- D

) L

=

V

R

+ S

L

(15)

Where SRAMP is the minimum internal slope value

of the compensation ramp. For stable operation,

α must be less than 1. The primary-side slew rate

can be estimated with Equation (16):



IN(MIN)

SENSE

M

V

R

L

(16)

The equivalent secondary-side voltage sensed

by the CS resistor can be calculated with

Equation (17):

MAX

IN(MIN)

SENSE

MAX

M

DV

R

(1 D

) L





−

(17)

External Protection through the PEP Pin

The PEP pin can be used to implement an over-

temperature

protection

(OTP)

function

for

external

power

devices

(e.g.

the

primary

MOSFET) by connecting a negative temperature

coefficient (NTC) resistor to this pin (see the

Primary External Protection (PEP) section on

page 22). Figure 18 shows OTP through the PEP

pin.

0.5V

PEP

1V

Figure 18: OTP through PEP

The sourcing current for PEP is IPEP. At working

temperatures, the NTC resistor should satisfy a

particular relationship, estimated with Equation

(18):

PEP

PEP

PEP-T

I

R

V



(18)

When the temperature increases, the NTC

resistance decreases. Figure 19 shows the

typical

waveform

for

NTC

resistance

vs.

temperature.

10

2

10

1

10

-1

10

-2

1

-20

0

20

40

60

80

100 120

Temperature(°C)

B=3450

B=3900

B=4100

Figure 19: NTC Resistance vs. Temperature

IPEP can also meet the condition at the protected

temperature value, calculated with Equation (19):

PEP

PEP

PEP T

I

R

V

−



(19)