MP3388S—55V, 8-STRING, STEP-UP, WHITE LED DRIVER
MP3388S Rev.1.02 www.MonolithicPower.com 9
9/28/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2016 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
sequence: either V
IN
or the PWM dimming signal
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 V
OUT
, then decrease the
input-voltage rise-time (). For a 6-string LED
application, select less than 20ms as shown in
Figure 3(b)
(a)
V
IN
0V
4.5V
τ
(b)
Figure 3: Input Voltage Rise-Time Indicator for
a 6-String LED Application
Note: Use any power sequence if the V
IN
rise-time from 0V to 4.5V is less than 20ms.
