LP3950 Datasheet, PDF (14/31 Pages) National Semiconductor (TI) – Color LED Driver with Audio Synchronizer

Magnetic Boost DC/DC Converter Electrical Characteristics (Continued)
Limits in standard typeface are for T_J = +25˚C. Limits in boldface type apply over the operating ambient temperature range
(−40˚C ≤ T_A ≤ +85˚C). Unless otherwise noted, specifications apply to Figure 1 with: V_DD1 = V_DD2 = V_DDA = 2.8V, C_VDD1 =
C_VDD2 = C_VDDA = C_VDDIO = 100 nF, C_OUT = C_IN = 10 µF, C_VREF = 100 nF, L₁ = 4.7 µH and f_BOOST = 2.0 MHz (Note 12).
Symbol
Parameter
Conditions
Min
Typ
Max Units
RDS_ON
f_PWF
Switch ON Resistance
PWM Mode Switching
Frequency
V_DD1,2 = 2.8V, I_SW = 0.5A
RT = 82 kΩ
freq_sel[2:0] = 1XX
0.4
0.7
Ω
2.0
MHz
Frequency Accuracy
2.7 ≤ VDD_1,2 ≤ 2.9
RT = 82 kΩ
−6
±3
+6
%
−9
+9
t_PULSE
Switch Pulse Minimum
Width
No Load
25
ns
t_STARTUP Startup Time
I_{CL_OUT} SW Pin Current Limit
15
ms
700
800
900
mA
500
1000
Boost Standby Mode
User can set the boost converter to STANDBY mode by writing the register bit EN_BOOST low when there is no load to avoid
idle current consumption. When EN_BOOST is written high, the converter starts in PFM (Pulse Frequency Modulation) mode for
10 ms and then goes to PWM (Pulse Width Modulation ) mode. All RGB outputs are off during the 10 ms delay.
Boost Output Voltage Control
User can control the boost output voltage by eight-bit boost output voltage register according to the following table.
BOOST[7:0]
Register 0D’h
Binary
Hex
0000 0000 00
0000 0001 01
0000 0011 03
0000 0111 07
0000 1111 0F
BOOST Output
Voltage
(typical)
4.10
4.25
4.40
4.55
4.70
BOOST[7:0]
Register 0D’h
Binary
Hex
0001 1111 1F
0011 1111 3F
0111 1111 7F
1111 1111 FF
BOOST Output
Voltage
(typical)
4.85
5.00 Default
5.15
5.30
Boost Frequency Control
The register ‘boost frequency’ has address 0C’h. The default value after reset is 07’h. ‘x’ means don’t care.
FREQ_SEL[2:0]
1xx
01x
Frequency
2.00 MHz
1.67 MHz
FREQ_SEL[2:0]
001
Frequency
1.00 MHz
www.national.com
14