LP3958

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SNVS423C – JANUARY 2006 – REVISED MARCH 2013

Vin = 3.6V, Vout = 18.0V if not otherwise stated

Functionality of Keypad LED Outputs (KEY1, KEY2, KEY3)

LP3958 has three individual keypad LED output pins. Output pins can be used in switch mode or constant

current mode. Output mode can be selected with the control register (address 00H) bit CC_SW. If the bit is set

high, then keypad LED outputs are in switch mode, otherwise in constant current mode. These modes are

described later in separate chapters.

Keypad LED output control can be done in three ways:

1. Defining the expected balance and brightness in Keypad register (address 01H)

2. Direct setting each LED ON/OFF via Keypad control register (address 00H)

3. External PWM control

BRIGHTNESS CONTROL WITH KEYPAD REGISTER

If the keypad LED output is used by defining the balance and brightness in the Keypad register, then one needs

to set EN_KEYP bit high and KEYP_PWM bit high in the Control register (address 00H). K1SW, K2SW and

K3SW are used to enable each LED output, enabled when written high. CC_SW defines the LED output mode. A

single register is used for defining the balance and brightness for keypad LED output:

KEYPAD REGISTER (01H)

Name

Bit

Description

BALANCE[2:0]

6:4

Balance of KEY1, KEY2 and KEY3 outputs

BRIGHT[2:0]

3:1

Brightness control

OVL

0

Overlapping mode selection:

0 = non-overlapping mode

1 = overlapping mode

Brightness control is logarithmic and is programmed as follows:

Table 2.

Bright[2:0]

Brightness [%]

Ratio to max

brightness

000

0

0

001

1.56

1/64

010

3.12

1/32

011

6.25

1/16

100

12.5

1/8

101

25

1/4

110

50

1/2

111

100

1/1

The LED balance can be selected as follows. This is valid only in non-overlapping mode.

Table 3.

Balance

KEY1

KEY2

KEY3

[2:0]

active [%]

active [%]

active [%]

000

100

0

0

001

0

100

0

010

0

0

100

011

50

50

0

100

0

50

50

101

50

0

50

110

33

33

33

111

50

25

25

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