Datasheet
www.ti.com
Q3
I
DRVP
DRVP
Current
Control
Soft Start
FBP
Cfly
Vs
R5
R6
C13
0.47 F
VGH
23 V/50 mA
SUP = V
IN
for V
S
> = 15 V
SUP = V
S
for V
S
< = 15 V
V
out
1.213
1
R5
R6
R5 R6
V
out
V
FB
1
R6
V
out
1.213
1
(1)
Negative Charge Pump
V
out
V
REF
R3
R4
1.213 V
R3
R4
R3 R4
V
out
V
REF
R4
V
out
1.213
(2)
TPS65150
SLVS576 – SEPTEMBER 2005
DETAILED DESCRIPTION (continued)
Figure 17. Extract of the Positive Charge Pump Driver
If higher output voltages are required another charge pump stage can be added to the output, as shown in Figure
21 at the end of the data sheet. To minimize quiescent current a high impedance feedback divider should be
used. The top feedback resistor should not be selected larger than 1M Ω .
Setting the output voltage:
The negative charge pump provides a regulated output voltage set by the external resistor divider. The negative
charge pump operates very similar to the positive charge pump with the difference that the voltage on the supply
pin SUP is inverted. The maximum output voltage for a single stage charge pump inverter is VGL = (–VSUP) +
Vdrop. Vdrop is the voltage drop across the external diodes and internal charge pump MOSFETs.
Setting the output voltage:
The lower feedback resistor value, R4, should range between 40 k Ω to 120 k Ω ; or, the overall feedback
resistance should be within 500 k Ω to 1 M Ω . Smaller values load the reference too heavily; and larger values
may cause stability problems. The negative charge pump requires two external Schottky diodes. The peak
current rating of the Schottky diode has to be twice the load current of the output. For a 20-mA output current,
the BAT54 dual Schottky diode is a good choice.
14