Datasheet

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     
SGLS246A − JUNE 2004 − REVISED JUNE 2008
3
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
Terminal Functions
TERMINAL
I/O
DESCRIPTION
NAME NO.
I/O
DESCRIPTION
C
FLY+
5 Positive terminal of the flying capacitor C
(fly)
C
FLY−
3 Negative terminal of the flying capacitor C
(fly)
GND 4 Ground
IN 2 I Supply input. Connect to an input supply in the 1.6-V to 5.5-V range. Bypass IN to GND with a capacitor that has the
same value as the flying capacitor.
OUT 1 O Power output with V
O
= −V
I
Bypass OUT to GND with the output filter capacitor C
O
.
detailed description
operating principle
The TPS60400, TPS60401 charge pumps invert the voltage applied to their input. For the highest performance,
use low equivalent series resistance (ESR) capacitors (e.g., ceramic). During the first half-cycle, switches S2
and S4 open, switches S1 and S3 close, and capacitor (C
(fly)
) charges to the voltage at V
I
. During the second
half-cycle, S1 and S3 open, S2 and S4 close. This connects the positive terminal of C
(fly)
to GND and the
negative to V
O.
By connecting C
(fly)
in parallel, C
O
is charged negative. The actual voltage at the output is more
positive than −V
I
, since switches S1–S4 have resistance and the load drains charge from C
O
.
C
(fly)
1 µF
S2
S1
S3
S4
C
O
1 µF
V
O
(−V
I
)
GND
V
I
GND
Figure 1. Operating Principle
charge-pump output resistance
The TPS6040x devices are not voltage regulators. The charge pumps output source resistance is
approximately 15 Ω at room temperature (with V
I
= 5 V), and V
O
approaches –5 V when lightly loaded. V
O
will
droop toward GND as load current increases.
V
O
= −(V
I
– R
O
× I
O
)
R
O
[
1
ƒosc C
(fly)
) 4
ǒ
2R
SWITCH
) ESR
CFLY
Ǔ
) ESR
CO
R
O
= output resistance of the converter
(1)