STEP UP, 4 STRINGS, MAX. 350MA/STRING ANALOG AND PWM DIMMING, WHITE LED CONTROLLER

MP3398A Rev. 1.04

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16

5/26/2017

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amplitude of the PWM signal is 1.5V and the low

level should be less than 0.4V.

Table 1

—The Range of PWM Dimming Duty

100<f

200

0.30%

100%

200<f

500

0.75%

100%

500<f

1k

1.50%

100%

1k<f

2k

3.00%

100%

2k<f

5k

7.50%

100%

5k<f

10k

15.00%

100%

10k<f

20k

30.00%

100%

2. Analog Dimming

For analog dimming, apply a PWM signal or a

DC voltage signal to ADIM pin. An internal RC

filter (10Mohm resistor and 100pF capacitor) is

integrated to this pin. So, if a PWM signal applied

to this pin, >20kHz frequency is recommended to

get a better PWM signal filtering performance

and make sure the amplitude voltage is higher

than 1.5V and low level voltage is less than 0.4V

with >15mV/ns slope rate for falling/rising edge.

For DC signal input, please apply a DC input

signal range from 0.4V to 1.5V to linearly set the

LED current from 0% to 100%.

Expanding LED Channels

The MP3398A can expand the number of LED

channels by using two or three MP3398A in

parallel. To connect two MP3398A for a total of 8

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 8 strings LEDs. The slave IC

MOSFET driving signals are not used; the boost

converter can be only driven by the master IC.

tie it to ground. Apply the EN and DIM signals to

both ICs.

Layout Considerations

The circuit layout for the MP3398A requires

special attention to reduce EMI noise.

The loop from the external MOSFET (M1),

through the output diode (D1) and the output

capacitor (C2, C3) carry a high-frequency pulse

current and must be as small and short as

possible (See Figure 3).

Figure 3

—Layout Consideration

All logic signals refer to the signal ground. in

order

to

reduce

the

noise

affection,

it

is

recommend to separate the power ground(PGND)

and signal ground(GND), then connect PGND

and GND together.