MP3387A ― 6-STRINGS, MAX 80MA/STRING, STEP-UP, WHITE LED DRIVER

MP3387A Rev. 1.0

www.MonolithicPower.com

11

5/17/2017

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improves the low LED current dimming ratio

and prevents troublesome audible noise issues.

If MIX is pulled low, the MP3387A works with

direct PWM dimming mode. The LED current is

chopped following the direct PWM dimming

signal duty cycle and frequency. The average

Output Over-Voltage Protection and Short

Protection

In some unexpected cases, to prevent the IC

from continuing to charge the output voltage,

the MP3387A uses an OVP function to protect

the components from being damaged by the

output voltage. If the OVP high-protection

threshold point (1.2V) has been reached, the

chip stops switching and the output voltage

drops. Switching resumes if the OVP point

drops below the recovery threshold.

The MP3387A can also achieve an output short

to GND or diode open protection by detecting

the OVP voltage. The IC works in normal

switching mode only when the OVP 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 (but not all strings) are

open, the respective LEDX pins are pulled to

ground, and the IC continues charging the

output voltage until OVP reaches the 1.2V

protection threshold. The chip stops switching

and marks off the open strings that have an

LEDX pin voltage lower than 275mV. Once

marked, the remaining LED strings force the

output voltage back into the correct regulation.

The string with the largest voltage drop

determines the output regulation. The marked-

off strings can resume normal operation after

they are connected back to the system.

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

IC continues charging the output voltage until

the OVP voltage reaches the 1.2V threshold

and marks off the LED current regulator. The IC

resumes normal current regulation until VIN or

EN is reset.

Short-String Protection

The MP3387A monitors the LEDX pin voltage

to determine if a short string occurs. If one or

more strings are short, the respective LEDX

pins are 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

longer

than

1.6ms

(fsw=1.25MHz),

the

corresponding

string

current regulator is disabled and disconnects

from the output voltage loop regulation. The

LED string resumes normal current regulation

when the short condition is removed.

Thermal Shutdown

To prevent the IC from operating at exceedingly

high

temperatures,

thermal

shutdown

is

implemented 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

20°C.