CAT3636

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10

Register Configuration and Programming

Table 6. REGISTER ADDRESS AND DATA

Register

Address

Pulses

Description

Bits

DATA Pattern

Bit 3

Bit 2

Bit 1

Bit 0

REG1

1

Bank Enable and IMODE

4

IMODE

ENA

ENB

ENC

REG2

2

Global Current Setting

4

See Table 8 for values

REG3

3

Bank A Current Setting

4

REG4

4

Bank B Current Setting

4

REG5

5

Bank C Current Setting

4

REG6

6

Return Lockout

1

RTLKO

Register REG1 allows to set the mode and select the pairs

of LEDs to be turned on. A low LED current mode exists to

allow for very low current operation under 4 mA per

channel. If IMODE equals 1, the high current range is

selected up to 32 mA. If IMODE is set to 0, all currents are

divided by 8. Each bank of LEDs (A, B or C) can be turned

on independently by setting the respective bit ENA, ENB,

ENC to 1, as shown in Table 7. For example, to enable all 6

LEDs in low current mode, REG1 is programmed to 0111

binary (9 data pulses).

Table 7. REG1 REGISTER SETTING

Data

Pulses

REG1 Value

(binary)

IMODE

Bank Enable

ENA

ENB

ENC

0

0000

0

−

−

−

1

1111

1

On

On

On

2

1110

1

On

On

−

3

1101

1

On

−

On

4

1100

1

On

−

−

5

1011

1

−

On

On

6

1010

1

−

On

−

7

1001

1

−

−

On

8

1000

1

−

−

−

9

0111

0

On

On

On

10

0110

0

On

On

−

11

0101

0

On

−

On

12

0100

0

On

−

−

13

0011

0

−

On

On

14

0010

0

−

On

−

15

0001

0

−

−

On

16

0000

0

−

−

−

Register REG2 allows to set the same current for all 6

channels. REG3, REG4, REG5 allow to set the current

respectively in banks A, B and C. The three banks can be

programmed with independent current values.

Table 8. REG2−5 CURRENT SETTING REGISTERS

Data

Pulses

REGx Value

(binary)

LED Current

IMODE = 0

LED Current

IMODE = 1

0

0000

0.0 mA

2 mA

1

1111

3.75 mA

32 mA

2

1110

3.5 mA

30 mA

3

1101

3.25 mA

28 mA

4

1100

3 mA

26 mA

5

1011

2.75 mA

24 mA

6

1010

2.5 mA

22 mA

7

1001

2.25 mA

20 mA

8

1000

2 mA

18 mA

9

0111

1.75 mA

16 mA

10

0110

1.5 mA

14 mA

11

0101

1.25 mA

12 mA

12

0100

1 mA

10 mA

13

0011

0.75 mA

8 mA

14

0010

0.5 mA

6 mA

15

0001

0.25 mA

4 mA

16

0000

0.0 mA

2 mA

REG6 contains the return lockout (RTLKO) bit. This

stops the charge pump returning to 1x mode. One pulse sets

it to 1. Two pulses or no pulses set RTLKO to 0. When

RTLKO is set to 1, the charge pump cannot automatically

return to 1x mode when in one of the charge pump modes.

The device can however move from 1x to 1.33x to 1.5x to

2x if the input voltage is not sufficient to drive the

programmed LED currents.

REG6 also triggers a charge pump reset as soon as it is

addressed. This forces the charge pump to start from 1x

mode and reassess the correct mode it should be in to drive

the LEDs most efficiently. If the input voltage has risen or

the device has been reprogrammed to other LED values, it

is recommended to trigger this reset allowing the charge

pump to run in the most efficient mode.

The CAT3636 enters a “zero current” shutdown mode if

EN/SET is held low for 1.5 ms or more. All registers are

reset back to zero when the device is placed in shutdown.