MP3385A – 4-STRING WLED CONTROLLER WITH I

MP3385A Rev. 1.01

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23

8/29/2017

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To ensure that the chip functions properly, an

appropriate OVP voltage is needed. The

recommended OVP point is about 1.1 to 1.2

times higher than the output voltage for normal

operation. If the OVP pin is connected to the

anode of the LED load, the OVP voltage is set

by the OVP4:0 bits in register 05H. It is not

recommended to set the OVP value higher than

80V, considering the LED return pin voltage

rating.

If the MP3385A is applied for >80V output

voltage

applications

through

an

external

between the anode of the LED and OVP pins to

change the over-voltage point of the output

(14):

OVP

OVP

R(kΩ)+1600

V(V)=

*1.9

40

(14)

Where the OVP4:0 bit in register 05H is the set

default.

Expanding LED Channels

The MP3385A expands the number of LED

channels by using two or three ICs in parallel.

To connect two ICs for a total of eight LED

strings, tie the VCC pins of the master IC and

the slave IC together to power the slave IC

internal logic circuitry. Tie the COMP pins of the

slave IC and the master IC together to regulate

the voltage of all eight strings. The slave IC

MOSFET driving signals are not used. The

boost converter can be driven only by the

master IC. Do not leave IS of the slave IC

floating; tie it to ground. Apply the EN and DIM

signals to both ICs. The master IC's OVP

should be higher than the slave IC's OVP.

PCB Layout Guidelines

Efficient PCB layout is critical to reduce EMI

noise and achieve stable operation. For best

results, refer to the guidelines below.

1. Keep the loop from the external MOSFET

through the output diode and the output

capacitor as small and short as possible

since they carry a high-frequency pulse

current.

2. Separate the power ground (PGND) and

signal ground (GND).

3. Connect PGND and GND together. All logic

signals refer to the signal ground to reduce

noise affection.

4. Place the ceramic capacitors for VIN and

VCC as close as possible.