LP3958 Datasheet, PDF (13/36 Pages) National Semiconductor (TI) – Lighting Management Unit with High Voltage Boost Converter

LP3958
www.ti.com
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:
Name
BALANCE[2:0]
BRIGHT[2:0]
OVL
KEYPAD REGISTER (01H)
Bit
Description
6:4
Balance of KEY1, KEY2 and KEY3 outputs
3:1
Brightness control
0
Overlapping mode selection:
0 = non-overlapping mode
1 = overlapping mode
Brightness control is logarithmic and is programmed as follows:
Bright[2:0]
000
001
010
011
100
101
110
111
Table 2.
Brightness [%]
0
1.56
3.12
6.25
12.5
25
50
100
Ratio to max
brightness
0
1/64
1/32
1/16
1/8
1/4
1/2
1/1
The LED balance can be selected as follows. This is valid only in non-overlapping mode.
Balance
[2:0]
000
001
010
011
100
101
110
111
Table 3.
KEY1
active [%]
100
0
0
50
0
50
33
50
KEY2
active [%]
0
100
0
50
50
0
33
25
KEY3
active [%]
0
0
100
0
50
50
33
25
Copyright © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LP3958
Submit Documentation Feedback
13