ILED (mA) | 25 x 0.85

[44 ± {(N+1)/2.91}]

LM3538

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SNVS674A – JUNE 2011 – REVISED MAY 2013

Table 5. Control Register Map (continued)

Hex

Read/W

Default Value

Register Name

Bit(s)

Bit Mnemonic and Description

Addr.

rite

After Reset

GROUP A

dxa

A0

[6:0]

R/W

x0000000

BRIGHTNESS

Sets Brightness for Group A. 128 steps, 1111111 = Fullscale.

alsZT

[5:3]

R/W

xx000xxx

Sets the Brightness Zone boundary used to enable and disable

GROUP B

Group B diodes based upon ambient lighting conditions.

B0

BRIGHTNESS

dxb

[2:0]

R/W

xxxxx000

Sets Brightness for Group B. 8 steps, 111 = Fullscale.

en_ldo4

[3]

R/W

xxxx0xxx

'1' = Regulator 4 enabled.

'0' = Regulator 4 disabled.

en_ldo3

[2]

R/W

xxxxx0xx

'1' = Regulator 3 enabled.

'0' = Regulator 3 disabled.

C0

LDO ENABLE

en_ldo2

[1]

R/W

xxxxxx0x

'1' = Regulator 2 enabled.

'0' = Regulator 2 disbaled.

en_ldo1

[0]

R/W

xxxxxxx0

'1' = Regulator 1 enabled.

'0' = Regulator 1 disbaled.

ldo1_vout

C1

LDO1 VOUT

[4:0]

R/W

xxx11000

Regulator 1 output voltage programming. See Table 4 for voltage

options.

ldo2_vout

C2

LDO2 VOUT

[4:0]

R/W

xxx01100

Regulator 2 output voltage programming.

ldo3_vout

C3

LDO3 VOUT

[4:0]

R/W

xxx01100

Regulator 3 output voltage programming.

ldo4_vout

C4

LDO4 VOUT

[4:0]

R/W

xxx11000

Regulator 4 output voltage programming.

Current Control Registers

A0 GROUP A BRIGHTNESS

This is the LED driver current control register for Group A. The register is effective when the ALS isn't used. The

resolution is 7 bits, so in linear dimming mode the step size from zero up to full brightness is fixed (25.0mA/127)

= 197µA. Exponential dimming scheme provides a more fine-grained level of control over low level LED currents.

Group A exponential dimming curve current can be approximated by the following equation (where N = the

decimal value stored in the Group A Brightness register):

Current vs. code is shown below.

Figure 25. LED current (typ.) vs. register code, exponential dimming curve

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