STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER

MP3398A Rev. 1.04

www.MonolithicPower.com

13

5/26/2017

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When a DC signal is applied to ADIM pin, the

voltage range in 0.4V to 1.5V directly sets the

LED current linearly from 0% to 100%.

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. If the

OVP point has been triggered for >4us, the chip

stops switching and marks 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 MP3398A will always attempt to light at

least one string. If all strings are open, the

MP3398A shuts down the step-up converter.

The strings will remain in this marked state until

the chip reset.

Short String Protection

The MP3398A 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

6.3V, 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. In order to prevent mis-triggering

short LED protection when open LED string or

sharp ADIM, the short LED protection function

is disabled when Vledx of all used LED

channels are higher than 1.5V.

Inductor/Diode short Protection

To prevent the IC and external MOSFET

damage when external inductor is shorted,

MP3398A has the protection mode in two

following methods. When inductor is shorted,

the output can not maintain enough energy to

load the LED and the output voltage will drop.

Thus, the COMP (the error amplifier output)

voltage tends to rise till be clamped high, when

it lasts longer than 512 switching cycles the IC

turns off and latches. In some cases that the

COMP voltage can not be clamped to high

when inductor is shorted, the IC also provides

the protection mode by detecting the current

flowing through power MOSFET. In this mode,

when the current sense voltage across sense

resistor (connected between MOSFET and

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.

When

the

die

temperature

shutdowns and recovers to normal operation

when

die

temperature drops below lower

threshold. Typically, the hysteresis value is

25°C.