MP3373, 8 STRINGS, WLED CONTROLLER WITH EXTERNAL TRANSISTOR

MP3373 Rev. 1.02

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12

8/16/2016

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threshold value. Once the mark-off operation

completes, the remaining LED strings will force

the output voltage back into tight regulation.

The string with the highest voltage drop is the

ruling string during output regulation. The

MP3373 always tries to light at least one string

and if all strings in use are open, the MP3373

shuts down the step-up converter. The part will

maintain mark-off information until the part

shuts down.

Short String Protection

The MP3373 monitors the CTLX pin voltages to

determine if a short string fault has occurred. If

one or more strings are shorted, the respective

CTLX pins tolerate high voltage stress. If the

CTLX pin voltage is higher than short protection

threshold for 4096 switching clocks, the fault

string is marked OFF and disabled. Once a

string is marked OFF, it disconnects from the

closed control loop of feedback. The marked

LED strings shut off completely until the part

restarts. If all strings are shorted together, the

Short String Protection is disabled.

Inductor/Diode short Protection

To prevent the IC and external MOSFET

damage

when

external

inductor/diode

is

shorted, MP3373 provides the protection mode

by detecting the current flowing through power

MOSFET. In this mode, when the current sense

voltage across sensing resistor (connected

and lasts for 4 switching cycles, the IC turns off

and latches.

Thermal Shutdown Protection

To prevent the IC operate at exceedingly high

temperature, thermal shutdown is implemented

in this chip by detecting the silicon die

temperature. The IC shutdowns when the die

temperature exceeds the upper threshold and

recovers

to

normal

operation

when

die

temperature drops below lower threshold.

Typically, the hysteresis value is 25°C

Over Voltage Protection

In some unexpected conditions, if OVP voltage

is greater than 2.5V, the gate driver stops

switching and thus, the output voltage starts

discharging. When the OVP voltage drops

lower than lower threshold caused by a OVP

hysteresis value, typical value 100mV, the gate

driver resumes to normal switching again.

If OVP voltage is greater than 3V for 4

switching cycles, MP3373 will turn off and latch

until VIN or EN is reset.

Unused Strings Connection

In default normal mode, all 8-channel current

sources are regulated in a closed feedback

control loop. In some cases, if one or more

channels

are

not

used,

connect

the

corresponding CTLX pin to GND. MP3373 will

detect it automatically during IC startup and

remove the unused channels from the closed

control loop.

Phase Shift Function

If PSEN pin is float, in PWM dimming mode, all

8-channel current sources are phase-shifted by

reduce inrush current and eliminate audible

noise, i.e., Channel 1 directly follows PWM

channels are unused by connecting respective

CTLX to GND, the phase shift phase detection

circuit can automatically change the phase shift

delay time. For example, if two channels are not

used by connecting CTRL7 and CTRL8 pin to

GND, the phase shift delay is automatically

connecting CTRL5, CTRL6, CTRL7 and CTRL8

pin to GND, the phase shift delay is

marked-off channels caused by short/open LED

string protection during operation will not

change the phase shift delay time.

If phase shift function is not used, connect

PSEN pin to GND.