MP3388S—50V, 8-STRING, STEP-UP, WHITE LED DRIVER

MP3388S Rev.1.01

www.MonolithicPower.com

9

10/29/2012

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© 2012 MPS. All Rights Reserved.

OPERATION

The MP3388S employs a constant-frequency,

peak-current–mode step-up converter and 8

channels of regulated current sources to regulate

up to 8 strings of white LEDs.

Internal 5V Regulator

The MP3388S includes an internal linear regulator

(VCC). When VIN exceeds 5.5V, this regulator

provides a 5V power supply for the internal

MOSFET switch gate driver and the internal

control circuitry. VCC drops to 0V when the chip

shuts down. In applications where VIN is less than

5.5V, tie VCC and VIN together. The MP3388S

features under-voltage lockout (UVLO). The chip

is disabled until VCC exceeds the UVLO

threshold. The UVLO hysteresis is approximately

200mV.

System Startup

When the MP3388S is enabled, the chip checks

the topology connection first. The VFAULT pin

slowly turns on the external fault disconnection

PMOS. And after a 400µs delay, the chip monitors

the OVP pin to check for the Schottky diode or if

the boost output is shorted to GND. If the OVP

voltage is below 70mV, the chip is disabled and

the external PMOS is turned off together. The

MP3388S also checks other safety limits,

including UVLO and OTP if the OVP test passes.

If the circuit passes all tests, then the MP3388S

uses an internal soft-start to boosting the step-up

converter.

For best results, use the following start-up

first, and then the enable signal (see Figure 2).

The MP3388S does not require a power-off

sequence (see Figure 4)

(a)

(b)

Figure 2: Recommended Start-Up Sequence

If using any other start-up sequence, as shown in

Figure 3(a), and the unused LEDx pins are not

connected

to

then

decrease

the

input-voltage rise-time (τ). For a 6-string LED

application, select τ less than 20ms as shown in

Figure 3(b)

(a)

0V

4.5V

τ

(b)

Figure 3: Input Voltage Rise-Time Indicator for

a 6-String LED Application

Note:

rise-time from 0V to 4.5V is less than 20ms.