MP3387L ― STEP UP, 6STRINGS,WHITE LED DRIVER

MP3387L Rev. 1.11

www.MonolithicPower.com

10

3/29/2016

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range of 24kHz~27.5kHz from 100Hz~20kHz of

the input PWM dimming signal frequency. By

doing this, MP3387L not only improves the low

LED current dimming ratio but also avoids the

troublesome audible noise issue.

If MIX pin is pulled to low, MP3387L works

under direct PWM dimming mode. The LED

just chopped following to the direct PWM

dimming signal duty cycle and frequency. The

Output Over Voltage Protection & Short

Protection

In some unexpected cases, in order to avoid

the IC keeping charging the output voltage,

MP3387L has OVP function to protect the

components from being damaged by output

voltage. If the OVP high protection threshold

point 1.2V has been reached, the chip stops

switching and thus, the output voltage drops.

The switching resumes to normal if the OVP

point drops below the recovery threshold.

In addition, MP3387L can achieve output short

to GND or Diode open protection by detecting

OVP pin voltage. The IC works in normal

switching only the OVP pin voltage is higher

than 80mV.

Open String Protection

Open string protection is achieved by detecting

both the OVP pin and the LED (1 to 6) pins. If

one or more strings (Not all strings) are open,

the respective LEDX pins are pulled to ground

and the IC keeps charging the output voltage

until OVP reaches the 1.2V protection threshold,

the chip stops switching and marks off the open

strings which have an LEDX pin voltage lower

than 275mV. Once marked, the remaining LED

strings force the output voltage back into right

regulation. The string with the largest voltage

drop determines the output regulation. In

addition, the marked-off strings can resume to

normal operation after connected back to the

system.

If all 6 strings are open (LED bar is open), the

IC keeps charging the output voltage until OVP

pin voltage hits 1.2V threshold, then mark off

the LED current regulator. The IC resumes to

normal current regulation till VIN or EN is reset.

Short String Protection

The MP3387L monitors the LEDX pin voltage to

judge if the short string occurs. If one or more

strings are short, the respective LEDX pins will

be pulled up to the boost output and tolerate

high voltage stress. If the LEDX pin voltage is

higher than 5.5V, the short string condition is

detected on the respective string. When the

short string fault (LEDX over-voltage fault)

continues

for

greater

than

1.6ms,

the

corresponding

string

current

regulator

is

disabled and disconnects from the output

voltage loop regulation. The LED string will

resume to normal current regulation when the

short condition is removed.

Thermal Shutdown Protection

To prevent the IC from operating 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

20°C.