MPX2003

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

MPX2003 Rev. 1.0

MonolithicPower.com

19

8/5/2022

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

© 2022 MPS. All Rights Reserved.

OPERATION

The MPX2003 is an all-in-one flyback controller

that provides the benefits

of primary-side

regulation (PSR) and secondary-side regulation

(SSR).

The

MPX2003

achieves

accurate

regulation while reducing system complexity and

the total solution cost.

The MPX2003 implements a complete SSR

scheme.

Both

the

control

loop

and

the

modulation block are placed on the secondary

IC, so the driving signal of the synchronous

rectifier (SR) can match the driving signal of the

primary-side MOSFET. This allows the SR to

operate safely in continuous conduction mode

(CCM), which increases overall efficiency and

provides the robust design more flexibility.

PRIMARY IC FUNCTIONS

Start-Up with Brown-In/Brownout Detection

The IC is disabled when there is no power supply.

When a voltage is applied to the HV pin, VCC is

charged by an internal current source from HV.

Once VCC exceeds the HV current source turn-

off voltage (VCC-IOFF, typically 14.5V), the current

source stops charging.

To eliminate voltage drop influence on the

external resistor, brown-in/brownout protection

is enabled after the HV current source turns off.

If the HV voltage exceeds VHV-ON (typically

107V), a brown-in condition has occurred. The

primary IC turns on the HV current source to

charge VCC back to VCC-IOFF (to guarantee a

maximized start-up window) and operates in

normal start-up mode. Otherwise, it is treated as

a brownout condition. The primary IC’s operation

remains disabled. Meanwhile, VCC is charged

and discharged between VCC-IOFF and VCC-MIN.

Once VCC exceeds VCC-IOFF, the primary IC

begins monitoring the status of the secondary IC

before the primary IC runs into normal start-up

mode. There are three conditions for primary IC

start-up, described below.

1.

If the primary IC starts up normally when a

brown-in condition is detected, and the

primary IC does not detect any status from

the secondary IC, the primary IC starts

switching on its own. Once the secondary IC

is active, the primary IC stops switching

independently, and the secondary IC takes

control.

There is a time

limit on the primary IC’s start-

up period. Independent primary switching

stops when the timer (tOCP) runs out. This

means that if there is a fault condition (e.g.

an overload), the secondary IC may not start

up successfully. tOCP starts counting from soft

start.

Then

the

primary

over-current

protection (POCP) flag is set, and the

primary IC runs in a protection operation.

2. If the secondary IC is active before primary-

side switching begins, the primary IC does

not require independent switching. The

secondary IC takes control immediately after

the brown-in condition is detected.

3. If the protection status is detected before

start-up, the IC indicates a fault condition,

such as an overload on the secondary side.

In this scenario, the primary IC does not

switch at all, but sets the protection flag and

runs in a protection operation.

Figure 2 shows the start-up logic for the primary

IC.

VCC-IOFF

HVON

VCC-AUT

VCC

HVCS

PDRV

VIN

Start-Up

Secondary

Side

(1)

(3)

(2)

HVOFF

Brownout

Active

Fault

Active

Figure 2: Start-Up Logic for the Primary IC

Brownout Protection during Normal

Operation

To prevent power supply issues caused by an

insufficient

input

voltage,

the

primary

IC

implements brownout protection. If the HV

voltage is below VHV-OFF (typically 98V, which is

the internal B/O threshold), the brownout timer

starts running. If the HV voltage exceeds VHV-OFF,

the timer is reset. If the brownout timer reaches

tBO, the primary IC triggers brownout protection,

and VCC initiates hiccup operation while it is

between VCC-MIN (typically 8.3V) and VCC-IOFF.