LP38798_15 Datasheet, PDF (16/27 Pages) Texas Instruments – LP38798 High PSRR, Ultra-Low-Noise, 800-mA Linear Voltage Regulator for RF/Analog Circuits

LP38798
SNOSCT6B – MARCH 2013 – REVISED DECEMBER 2014
www.ti.com
7.5 Programming
7.5.1 Programming the Output Voltage
Current sourced from the SET pin, through R1 and R2, must be kept to less than 100 µA. The minimum allowed
value for R2 is 12.9 kΩ.
I_SET = V_FB / R2
(4)
R2_MIN = V_FB(MAX) / 100 μA
(5)
R2_MIN = 12.9 kΩ;
(6)
The values for R1 and R2 may be adjusted as needed to achieve the desired output voltage as long as the value
for R2 is no less than 12.9 kΩ. The maximum recommended value for R2 is 100 kΩ.
Equation 7 is used to determine the output voltage:
V_OUT = (V_FB × (1 + ( R1 / R2 ))) + V_OS
(7)
Alternately, Equation 8 can be used to determine the appropriate R1 value for a given R2 value:
R1 = R2 × (((V_OUT) / V_FB) – 1)
(8)
Table 1 suggests some ±1% values for R1 and R2 for a range of output voltages using the typical V_FB value of
1.200V. This is not a definitive list, as other combinations exist that will provide similar, possibly better,
performance.
TARGET V_OUT
1.5 V
1.8 V
2.0 V
2.5 V
3.0 V
3.3 V
5.0 V
Table 1. Typical R1 and R2 Values for Assorted Output Voltages
R1
4.22 kΩ
10.5 kΩ
10.0 kΩ
16.2 kΩ
21.0 kΩ
23.2 kΩ
47.5 kΩ
R2
16.9 kΩ
21.0 kΩ
15.0 kΩ
15.0 kΩ
14.0 kΩ
13.3 kΩ
15.0 kΩ
TYPICAL V_OUT
1.5 V
1.8 V
2.0 V
2.496 V
3.0 V
3.293 V
5.0 V
16
Submit Documentation Feedback
Product Folder Links: LP38798
Copyright © 2013–2014, Texas Instruments Incorporated