MP3383

– 4-STRING, MAX 80V VOUT, STEP-UP WLED CONTROLLER

MP3383 Rev. 1.0

MonolithicPower.com

15

5/2/2022

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Open-String Protection

Open-string protection is achieved through

detecting VOVP and LEDx voltage (VLEDx, where

“LEDx” can be LED1, LED2, LED3, and LED4).

If one or more strings are open, then the

respective LEDx pins are pulled to ground and

the IC continues charging VOUT until it reaches

the OVP threshold. If the OVP threshold is

triggered, then the chip stops switching and

marks off the strings for which VLEDx is below

100mV. Once marked, the remaining LED

strings force VOUT back to normal regulation. The

string with the largest voltage drop determines

the output regulation value.

The MP3383 always attempts to light at least

one string. If all strings are open, the MP3383

shuts down the step-up converter. The open

strings remain in this marked-off state until the

chip resets.

Short-String Protection

The MP3383 monitors VLEDx to determine

whether a short-string fault has occurred. If one

or more strings are short, then the respective

LEDx pins tolerate high-voltage stress. If VLEDx

exceeds the protection threshold for 16 switching

cycles (128 switching cycles, optionally), short-

string protection is triggered, and the fault string

is marked off and disabled. Once a string is

marked off, it disconnects from the VOUT loop

until VIN or EN restarts.

To prevent mistriggering a short LED protection

when the LED string is open, the short LED

protection function is disabled when VLEDx for all

used LED channels exceeds 2.1V.

For applications where

VOUT > 90V, use an

external MOSFET to carry the huge voltage

when the whole LED string is shorted.

Cycle-by-Cycle Current Limit

To prevent the external components from

exceeding their respective current stress ratings,

the IC employs cycle-by-cycle current-limit

protection. When the current-sense voltage

across the sense resistor (connected between

ISENSE and GND) reaches the cycle-by-cycle

current-limit threshold, the external MOSFET

turns off until the next clock cycle begins.

Short Inductor and Diode Protection

When the external inductor or diode is shorted,

the IC provides protection by detecting the

current flowing through the power MOSFET. If

the current-sense voltage across the sense

resistor (connected between ISENSE and GND)

exceeds the latch-off current limit threshold and

lasts for five switching cycles, the IC stops

switching and latches off.

Thermal Shutdown

The

MP3383

monitors

the

silicon

die

temperature to prevent the IC from operating at

exceedingly

high

temperatures.

If

the

die

temperature exceeds the threshold (TST), the IC

shuts down. Once the die temperature drops

below the lower threshold, the IC restarts and

resumes normal operation. The hysteresis value

is typically 25°C.