Datasheet

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SLVS324A − JULY 2001 REVISED NOVEMBER 2004
17
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APPLICATION INFORMATION
paralleling devices
Paralleling multiple TPS6040xs reduces the output resistance. Each device requires its own flying capacitor
(C
(fly)
), but the output capacitor (C
O
) serves all devices (see Figure 29). Increase C
O
’s value by a factor of n,
where n is the number of parallel devices. Equation 1 on page 3 shows the equation for calculating output
resistance.
TPS60400
OUT C1+
IN
C1− GND
1
2
3
5
4
C
(fly)
1 µF
C
I
1 µF
V
O
(−V
I
)
GND
V
I
GND
TPS60400
OUT C1+
IN
C1− GND
1
2
3
5
4
C
(fly)
1 µF
C
O
2.2 µF
+
Figure 29. Paralleling Devices
active-Schottky diode
For a short period of time, when the input voltage is applied, but the inverter is not yet working, the output
capacitor is charged positive by the load. To prevent the output being pulled above GND, a Schottky diode must
be added in parallel to the output. The function of this diode is integrated into the TPS6040x devices, which gives
a defined startup performance and saves board space.
A current sink and a diode in series can approximate the behavior of a typical, modern operational amplifier.
Figure 30 shows the current into this typical load at a given voltage. The TPS6040x devices are optimized to
start into these loads.
TPS60400
C1−C1+
53
OUT
IN
GND
1
2
4
C
I
1 µF
C
O
1 µF
C
(fly)
1 µF
Typical
Load
I
O
V
O
(−V
I
)
+V
−V
V
I
GND
60 mA
25 mA
0.4 V 1.25 V 5 V
Load Current
Voltage at the Load
0.4 V
Figure 30. Typical Load Figure 31. Maximum Start-Up Current