LP3944_14 Datasheet, PDF (11/17 Pages) Texas Instruments – RGB/White/Blue 8-LED Fun Light Driver

LP3944
www.ti.com
SNVS264 – MAY 2004
Table 9. LED States With Respect To Values in "B1" and "B0" (continued)
B1
B0
Function
1
0
Output dims
(DIM0 rate)
1
1
Output dims
(DIM1 rate)
Programming Example:
Dim LEDs 0 to 7 at 1 Hz at 25% duty cycle
1. Set PSC0 to achieve DIM0 of 1s
2. Set PWM0 duty cycle to 25%
3. Set PSC1 to achieve DIM1 of 0.2s
4. Set LEDs 0 to 7 to point to DIM0
Step
1
2
3
4
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
LEDs 0 to 7
Output = DIM0
Register Name
PSC0
PWM0
PSC1
LS0, LS1
Set to (Hex)
0x09F
0x40
0x1F
LS0 = 0xAA
LS1 = 0xAA
Reducing I_Q When LEDS are Off
In many applications, the LEDs and the LP3944 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 12. Methods to Reduce I_Q When LEDs Are Off
V_DD
LED 7
LP3944
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 13. Application Circuit
Copyright © 2004, Texas Instruments Incorporated
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