MP3394S—4-STRING, MAX 200mA/STRING WHITE LED DRIVER

MP3394S Rev. 1.03

www.MonolithicPower.com

10

3/21/2013

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For external PWM dimming, ground the BOSC

pin through a resistor, and apply an external

PWM signal to the DBRT pin.

For DC-input PWM dimming, apply a DC analog

signal to the DBRT pin, and connect a capacitor

on BOSC pin to ground. The DC signal is then

converted to a DPWM dimming signal with a

proportional oscillation frequency.

The brightness of the LED array is proportional to

the duty cycle of the DPWM signal. The DPWM

signal frequency is set by the capacitor from the

BOSC pin to ground.

Open String Protection

Open string protection is achieved through the

OVP pin and the LED (1 to 4) pins. If one or more

strings are open, the respective LEDX pins are

pulled to ground and the IC keeps charging the

output voltage until it reaches the over-voltage

protection (OVP) threshold. Then the chip marks

off the strings which have an LEDX pin voltage

lower than 196mV. Once marked, the remaining

LED strings force the output voltage back into

tight regulation. The string with the largest

voltage drop determines the output regulation.

The MP3394S will always attempt to light at least

one string. If all strings are open, the MP3394S

shuts down the step-up converter. The strings

will remain in this marked state until the chip

reset.

Short String Protection

The MP3394S monitors the LEDX pin voltages to

determine if a short string fault has occurred. If

one or more strings are shorted, the respective

LEDX pins tolerate high voltage stress. If an

LEDX pin voltage is higher than 6.1V, this

condition triggers the detection of a short string.

When a short string faults (LEDX over-voltage

fault) keeps for 4096 switching clocks, the fault

string is marked OFF and disabled. Once a string

is marked OFF, it disconnects from the output

voltage loop. The marked LED strings shut off

completely until the part restarts. If all strings are

shorted, the MP3394S will shut down the step-up

converter. The strings remain marked OFF until

the chip resets.

Thermal Shut Down Protection

When MP3394S die temperature exceeds the

thermal

protection

threshold,

the

thermal

protection is triggered. IC shuts down until EN

restart.