Datasheet

   
     
SLVS324A − JULY 2001 REVISED NOVEMBER 2004
16
WWW.TI.COM
APPLICATION INFORMATION
combined doubler/inverter
In the circuit of Figure 27, capacitors C
I
, C
(fly)
, and C
O
form the inverter, while C1 and C2 form the doubler. C1
and C
(fly)
are the flying capacitors; C
O
and C2 are the output capacitors. Because both the inverter and doubler
use part of the charge-pump circuit, loading either output causes both outputs to decline toward GND. Make
sure the sum of the currents drawn from the two outputs does not exceed 60 mA. The maximum output current at
V
(pos)
must not exceed 30 mA. If the negative output is loaded, this current must be further reduced.
TPS60400
OUT C1+
IN
C1− GND
1
2
3
5
4
C
(fly)
1 µF
C
O
1 µF
C
I
1 µF
−V
I
GNDGND
V
I
C
1
+
+
+
D
2
C
2
+
V
(pos)
+
I
I
≈ −I
O
+ 2 × I
O(POS)
Figure 27. TPS60400 as Doubler/Inverter
cascading devices
Two devices can be cascaded to produce an even larger negative voltage (see Figure 28). The unloaded output
voltage is normally −2 × V
I
, but this is reduced slightly by the output resistance of the first device multiplied by the
quiescent current of the second. When cascading more than two devices, the output resistance rises
dramatically.
TPS60400
OUT C1+
IN
C1− GND
1
2
3
5
4
C
(fly)
1 µF
C
O
1 µF
C
I
1 µF
V
O
(−2 V
I
)
GND
V
I
GND
TPS60400
OUT C1+
IN
C1− GND
1
2
3
5
4
C
O
1 µF
GND
+
+
+
C
(fly)
1 µF
Figure 28. Doubling Inverter