MP4658 – 4-STRING, 80V RETURN LED DRIVER WITH AC/DC FEEDBACK

MP4658 Rev. 1.0

MonolithicPower.com

13

10/13/2021

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impedance on ADIM is below

15kΩ, then the

RC filter constant is smaller and the ILED

rising/falling speed during PWM dimming is

faster. Soft PWM dimming for ILED helps reduce

the audible noise.

Protection Features

The MP4658 integrates sufficient protections for

the output voltage stage and LED driver stage.

The protections for the VOUT stage includes

system over-voltage protection (OVP) and open

feedback loop protection. Fault protections for

the

LED

driver

stage

include

open

LED

protection, short LED string protection, one or

more LED short protection and LEDx short to

ground protection.

Output Over-Voltage Protection (OVP)

The FB pin senses VOUT for regulation and OVP.

If VFB is 24% greater than VREF, the MP4658

triggers output OVP and the OPT pin is

clamped to 3.3V when the LED stage is off.

Output OVP is disabled when the LED stage is

on. The fault indicator outputs a low voltage

when output OVP is triggered.

Feedback Open Protection

If VFB is below 500mV, the IC latches off and

the fault indicator outputs a low voltage.

Open LED Protection

The LED string voltage is sensed by the OVP

pin. Open LED protection is achieved via the

OVP pin voltage and the LEDx (LED1~4) pin

voltage detections. If one or more LED strings

are open, the respective VLEDx is pulled to

ground and the LED string

’s output voltage

keeps increasing until the OVP pin

’s voltage

(VOVP) reaches the OVP threshold. When VOVP

reaches 2.4V and VLEDx is below 100mV, the

MP4658 triggers open LED protection. The IC

marks off the open string(s), meaning any that

have a VLEDx below 100mV. The remaining LED

strings discharge the output voltage and VOVP

decreases until it falls below the OVP threshold.

Then the LED control loop recovers and the

minimum VLEDx of the remaining LED strings is

regulated. If an LED open fault is triggered, the

fault indicator pin outputs a low voltage.

If all LED strings are open, all strings are

marked off and the LED control loop is disabled.

If an open all LED strings condition occurs, the

IC operation mode switches from constant

current (CC) mode to constant voltage (CV)

mode.

If VOVP exceeds 3V, the IC latches off. This

function protects the components from any out

of control condition (such as the LED output

voltage exceeding VOV_LED when the OPT pin is

not pulled high) and keeps the system safe.

LED Short Protection

VLEDx is used to indicate a short LED condition.

If an LED string is shorted, the respective VLEDx

increases significantly. If VLEDx exceeds 5V for

5ms, a short fault is triggered, and the MP4658

marks off this string. Other strings keep working

if they are not experiencing a short.

If short protection is triggered, the fault indicator

outputs a low voltage.

LEDx Short-to-Ground Protection

If COMP1 is saturated and VLEDx is low for 30ms,

the IC triggers LEDx short-to-ground protection.

The LED control loop is disabled, and the

output voltage is regulated in constant voltage

(CV) mode. If this protection is triggered, the

fault indicator outputs a low voltage.

The LED loop can recover from a fault condition

by toggling the ADIM or PDIM pin. Pull either

pin low for more than 30ms, then pull it high.

The fault condition should be removed, and the

fault indicator should reset.

Thermal Protection

Thermal protection is integrated in the MP4658.

If the die temperature exceeds the over-

temperature (OT) threshold (150°C), the IC

stops working until the die temperature falls to

125°C.