SM8134A

SEIKO NPC CORPORATION —8

FUNCTIONAL DESCRIPTION

Serial Interface

The SM8134A uses a 3-wire serial interface to control each setting. Input data on SDA is input MSB first in an

8 clock pulse cycle structure, with the first 4 cycles of data setting the mode and the next 4 the corresponding

mode data. Data bits on SDA are read as received data on the rising edges of the SCK clock after EN goes

HIGH. Only the leading 8 bits on SDA are read after EN goes HIGH and all subsequent input data bits are

ignored, but the received data is reflected in SM8134A operation with timing almost simultaneous with the EN

falling edge. Conversely, if less than 8 bits are input on SDA, the data is ignored to prevent incorrect operation.

All registers are write-only, and their status cannot be read. After power is applied, an internal power-ON reset

circuit initializes all registers to logic level LOW in standby mode. However, the possibility exists that there

may be insufficient reset time, depending on the VIN input voltage rise time and fall time, so reset mode (0H or

EH) should be expressly invoked after power is applied. There is no restriction in the input sequence when set-

ting parameters. However, since the parameters are set in the same order as the data input sequence and the

time taken from LED ON/OFF data input to LED dimming data input can exceed the soft start time, it is highly

advisable to enter the LED dimming data first. The charge pump circuit, that supplies the LED drive voltage,

starts whenever any parameter in address 5H (LED ON register) is set to 1, with the LED drive voltage output

on VOUT. Conversely, when all parameters in address 5H are set to 0, all other parameter data settings input

after reset are retained in standby mode. The serial interface pins EN, SDA, and CSK are CMOS inputs, thus

the input voltage on VIN must be a logic-level voltage and should not be left open circuit (floating).

Control Data

I

Mode selection

Mode selection data

Setting data

M1

M2

M3

M4

D1

D2

D3

D4

MSB

Data 1

Data 2

Data 3

Data 4

Data 5

Data 6

LSB

Control data input sequence

Mode data

0H

2H

4H

5H

EH

Other

Mode

Reset

DIN1 to 4 dimming

DIN5 dimming

LED ON

Reset

NPC test

M1-M2-M3-M4

L-L-L-L

L-L-H-L

L-H-L-L

L-H-L-H

H-H-H-L

−

SCK

M1

M2

EN

M3

M4

D1

D2

D3

D4

SDA