LP3943 Datasheet, PDF (13/21 Pages) National Semiconductor (TI) – RGB/White/Blue 16-LED Fun Light Driver

LP3943
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Step 4: Set PWM1 duty cycle to 50%
Step 5: Set LEDs 13, 14 and 15 off by loading the data into LS3 register
Step 6: Set LEDs 0 to 7 to point to DIM0
Step 7: Set LEDs 8 to 12 to point to DIM1
Step
1
2
3
4
5
6
7
Description
Set DIM0 = 1s
1 = (PSC0 + 1)/160
PSC0 = 159
Set duty cycle to 25%
Duty Cycle = PWM0/256
PWM0 = 64
Set DIM1 = 0.2s
0.2 = (PSC1 + 1)/160
PSC1 = 31
Set duty cycle to 50%
Duty Cycle = PWM1/256
PWM1 = 128
LEDs 13, 14 and 15 off
Output = HIGH
LEDs 0 to 7
Output = DIM0
LEDs 8 to 12
Output = DIM1
Register Name
PSC0
PWM0
PSC1
PWM1
LS3
LS0, LS1
LS2, LS3
SNVS256A – MAY 2004 – REVISED MAY 2004
Set to (Hex)
0x09F
0x40
0x1F
0x80
0x03
LS0 = 0xAA
LS1 = 0xAA
LS2 = 0xFF
LS3 = 0x03
REDUCING I_Q WHEN LEDS ARE OFF
In many applications, the LEDs and the LP3943 share the same V_DD, as shown in Typical Application Circuit.
When the LEDs are off, the LED pins are at a lower potential than V_DD, causing extra supply current (ΔI_Q). To
minimize this current, consider keeping the LED pins at a voltage equal to or greater than V_DD.
Figure 11. Methods to Reduce I_Q When LEDs Are Off
V_DD
LED 15
LP3943
LED 0
2.2 PF
V_OUT
V_IN
LM2750-5.0
2.7V to 5.5V
2.2 PF
CAP+
CAP-
C_FLY
1 PF
Figure 12. LP3943 With 5V Booster
Copyright © 2004, Texas Instruments Incorporated
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