MP3398E

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

MP3398E Rev. 1.02

www.MonolithicPower.com

12

7/31/2017

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Open-String Protection

Open-string protection is achieved through

detecting the voltage of OVP and LED (1 to 4).

If one or more strings are open, the respective

LEDX pins are pulled to ground, and the IC

continues charging the output voltage until it

reaches the over-voltage protection (OVP)

threshold. If the OVP point has been triggered,

the chip stops switching and marks off the

strings that have an LEDX pin voltage lower

than 200mV. 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 MP3398E always attempts to light at least

one string. If all strings are open, the MP3398E

shuts down the step-up converter. The strings

remain in this marked state until the chip resets.

Short-String Protection

The MP3398E 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 the

protection threshold, this condition triggers the

detection of a short-string fault. When a short-

string fault remains for 10ms, the fault string is

marked off and disabled. Once a string is

marked off, it disconnects from the output

voltage loop until VIN or EN restarts.

To prevent mistriggering a short LED protection

when the LED string is open, the short LED

used LED channels is higher than 2.1V.

Cycle-by-Cycle Current Limit

To prevent the external components from

exceeding their current stress ratings, the IC

employs cycle-by-cycle current-limit protection.

When the current exceeds the current limit

value, the IC latches off until the power resets.

Short Inductor/Diode Protection

When the external inductor or diode is shorted,

the IC provides protection by detecting the

current flowing through the power MOSFET.

When the current sense voltage across the

sense resistor (connected between ISENSE

and GND) reaches the current protection

threshold and lasts for eight switching cycles,

the IC stops switching and latches.

Thermal Shutdown

To prevent the IC from operating at exceedingly

high

temperatures,

thermal

shutdown

is

implemented by monitoring the silicon die

temperature.

When

the

die

temperature