MP4056GS datasheet(18/26 Pages) MPS

18 / 26 page

MP4056—TRIAC DIMMABLE, NON-ISOLATED OFFLINE LED CONTROLLER WITH APFC

MP4056 Rev.1.01

www.MonolithicPower.com

11/9/2016

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

Output Over-Voltage Protection (OVP)

Output over-voltage protection (OVP) prevents

the components from over-voltage damage. The

auxiliary winding voltage’s positive plateau is

proportional to the output voltage, so the OVP

block monitors this auxiliary winding voltage to

apply an OVP function, as shown in Figure 7.

Once the ZCD pin voltage exceeds VZCD_OVP, the

OVP signal is triggered, the gate driver turns off,

the IC works in its quiescent current mode. When

the

VCC

voltage

drops

below

the

UVLO

threshold, the IC shuts down and the system

restarts. The output OVP set point is calculated

as:







aux

ZCD2

out _ ovp

ZCD _ OVP

sec

ZCD1

ZCD2

Where:

Vout-ovp is the output OVP threshold,

Naux is the turns of auxiliary winding, and

Nsec is the turns of secondary winding

tOVP_LEB

Blanking

Vcc

ZCD

Auxiliary Winding

RZCD1

OVP

signal

VZCD_OVP

Latch

RZCD2

Figure 7: OVP Sampling Circuit

To avoid switch-off spikes mis-triggering OVP,

OVP sampling has a tOVP_LEB blanking period, as

shown in Figure 8.

VZCD

tOVP_LEB

Sampling Here

Figure 8: ZCD Voltage and OVP Sampling

Cycle by Cycle Current Limit

There is cycle by cycle current limit on the S pin,

when the voltage on S pin reaches VS_CLAMP_H

after a blanking time, the switching will turn off to

limit the peak current value.

Over-Current Protection (OCP)

The

has

internally-integrated

comparator for inductor OCP. When the gate is

on, the comparator is enabled. Over-current

occurs when VS exceeds VOCP after a blanking

time. The IC shuts down and restarts after VCC

drops below UVLO. The OCP function block

diagram is shown in Figure 9.

tLEB_OCP

OCP

VOCP

Gate

ILm

latch

Blanking

Figure 9: Over-Current Protection Circuit

LED Short Circuit Protection (SCP)

When the LED Short Circuit occurs, IC reduces

the switching frequency to 7kHz. The output

power at this condition is limited to a safe range.

ZCD Pin Short Circuit Protection

If ZCD pin voltage is less than VZCD_SC lasts

longer than tZCD_SC_LEB, it is recognized as ZCD

pin short circuit. The MP4056 stops the switching

until VCC drops below UVLO and restarts.

This prevents the components from over-voltage

damage if LED load opens while ZCD shorts at

the same time.

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