MP3398D – 4-STRING, 350MA/STRING, STEP-UP, WHITE LED CONTROLLER

MP3398D Rev. 1.0

www.MonolithicPower.com

13

5/23/2016

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2016 MPS. All Rights Reserved.

Open-String Protection

Open-string protection is achieved through the

OVP and LEDX (1 to 4) pins. 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 OVP

threshold. If the OVP point has been triggered

for more than 4µs, the chip stops switching and

marks 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 MP3398D always attempts to light at least

one string. If all strings are open, the MP3398D

shuts down the step-up converter. The strings

remain in this marked state until the chip resets.

Short-String Protection

The MP3398D 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 fault (LEDX

over-voltage fault) remains for 4096 switching

cycles, 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. Short LED protection can be

mistriggered by two events: when open LED

protection is triggered, or when the PWM duty

on ADIM goes from high to low in a short

amount of time. To prevent this, the short LED

of the working LED channels are higher than

1.5V.

Inductor and Diode Short Protection

To protect the IC and external MOSFET from

damage caused when the external inductor is

shorted, the MP3398D uses two protection

mode methods.

The first method occurs when the inductor is

shorted. The output is unable to maintain

enough energy to load the LED, causing the

output voltage to drop. Thus, the COMP voltage

(error amplifier output) rises until it is clamped

high. When the COMP voltage lasts for more

than 512 switching cycles, the IC turns off and

latches.

The second method occurs in cases where the

COMP voltage cannot be clamped high when

the inductor is shorted. The IC detects the

current flowing through the power MOSFET.

When the current sense voltage across the

sense resistor (connected between MOSFET

four switching cycles, the IC turns off and

latches.

Thermal Shutdown

To prevent the IC from operating at exceedingly

high temperatures, the MP3398D implements

thermal shutdown by detecting the silicon die

temperature.

When

the

die

temperature

down and resumes normal operation when the

die

temperature

drops

below

the

lower

threshold. Typically, the hysteresis value is

25°C.