Multiple-Output Regulator for

Automotive LCD Displays

A8603

13

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Programmable Regulators

The A8603 has four voltage regulators: AVDD, VCOM, VGL,

and VGH.

Target voltages of all four regulators are programmable by

internal registers. In addition, other features (such as startup

and shutdown sequences, Fault retry counter, etc.) can also be

programmed.

Table 2: Target Voltages

Output Regulator

Register

Min. Voltage (V)

Max. Voltage (V)

DAC # of Bits

DAC # of Steps

Step Size (mV)

AVDD

00

5 (Reg=0x00)

15 (0x7F)

7

127

78.74

VCOM

01, 02

2.5 (0x0000)

7.5 (0x01FF)

9

511

9.785

VGL

03

–3.6 (0x00)

–13.03 (0x3F)

6

63

–149.7

VGH

04

9.9 (0x00)

31.236 (0x7F)

7

127

168

*Note: AVDD must be at least 1.5V higher than VCOM, so not all combinations of VCOM and AVDD are possible.

Table 3: Startup Time Delay

Refer to Startup Timing Diagram on how those time delays are defined.

Timer

Min. Delay (ms)

Max. Delay (ms)

Step Size (ms)

Number of Bits

t1 = AVDD

0 (0x00)

25.5 (0xFF)

0.1

8

t2 = VCOM

0

25.5

0.1

8

t3 = VGL

0

25.5

0.1

8

t4 = VGH

0

25.5

0.1

8

Table 4: Shutdown Time Delay

Refer to Shutdown Timing Diagram on how those time delays are defined.

Timer

Min. Delay (ms)

Max. Delay (ms)

Step Size (ms)

Number of Bits

t5 = AVDD

0 (0x00)

25.5 (0xFF)

0.1

8

t6 = VCOM

0

25.5

0.1

8

t7 = VGL

0

25.5

0.1

8

t8 = VGH

0

25.5

0.1

8

Dithering:

Reg0x10 bit[0,1]: controls Dithering off, ±5%, 10% or 15%.

Power Sequence:

Reg0x10 bit4: By default VGL is enabled before VGH during power-up. But if this bit is set to ‘1’, then VGH is enabled first.

The target voltage for each output regulator is programmed by

writing to a register, according to the following equation:

Target_Voltage = Min_voltage + #steps × step_size

For example, to set AVDD to 12 V, the user should write ‘0x59’

to Reg0x00. This is because:

#steps = (Target_Voltage – Min_Voltage) / step_size

= (12 – 5) / 0.07874 = 88.9

So the content of Reg0x00 is 89 in decimal, or ‘0x59’ in hexa-

decimal.

Name

Register

Default

Min.

Max.

Step Size

Number of Bits

Watchdog Timer

0x09

51.2 (0x10) ms

9.6 (0x03) ms

99.2 (0x1F) ms

3.2 ms

5

Cooldown Timer

0x0B

102.4 (0x20) ms

9.6 (0x03) ms

201.6 (0x3F) ms

3.2 ms

6

Fault Retry Counter

0x0A

8 (0x08)

0 (0x00)

15 (0x0F)

1

4