Datasheet

LTC114 4
8
1144fa
For more information www.linear.com/LTC1144
Typical applicaTions
Negative Voltage Converter
Figure 8 shows a typical connection which will provide
a negative supply from an available positive supply. This
circuit operates over full temperature and power supply
ranges without the need of any external diodes.
The output voltage (pin 5) characteristics of the circuit
are those of a nearly ideal voltage source in series with a
56Ω resistor. The 56Ω output impedance is composed of
two terms: 1) the equivalent switched capacitor resistance
(see Theory of Operation), and 2) a term related to the
on-resistance of the MOS switches.
Figure 9. Voltage Doubler
Ultra-Precision Voltage Divider
An ultra-precision voltage divider is shown in Figure 10. To
achieve the 0.002% accuracy indicated, the load current
should be kept below 100nA. However, with a slight loss
in accuracy, the load current can be increased.
At an oscillator frequency of 10kHz and C1 = 10µF, the
first term is:
R
EQUIV
=
1
f
OSC
/ 2
( )
×C1
=
1
5×10
3
×10 ×10
−6
= 20Ω
Notice that the above equation for R
EQUIV
is not a capaci-
tive reactance
equation (X
C
= 1/ωC) and does not contain
a 2π term.
The exact expression for output impedance is extremely
complex, but the dominant effect of the capacitor is clearly
shown in Figure 5. For C1 = C2 = 10µF, the output imped
-
ance goes
from 56Ω at f
OSC
= 10kHz to 250Ω at f
OSC
=
1kHz. As the 1/(f × C) term becomes large compared to
the switch on-resistance term, the output resistance is
determined by 1/(f × C) only.
Voltage Doubling
Figure 9 shows a two-diode capacitive voltage doubler.
With a 15V input, the output is 29.45V with no load and
28.18V with a 10mA load.
Figure 8. Negative Voltage Converter
Figure 10. Ultra-Precision Voltage Divider
Battery Splitter
A common need in many systems is to obtain (+) and
(–) supplies from a single battery or single power supply
system. Where current requirements are small, the cir
-
cuit shown in Figure 11 is a simple solution. It provides
symmetrical
± output voltages, both equal to one half the
input voltage. The output voltages are both referenced to
pin 3 (output common).
Figure 11. Battery Splitter
1
2
3
4
8
7
6
5
+
+
10µF
10µF
V
+
2V TO 18V
V
OUT
= –V
+
T
MIN
≤ T
A
≤ T
MAX
1144 F08
LTC1144
1
2
3
4
8
7
6
5
+
+
+
+
V
IN
2V TO 18V
V
OUT
= 2(V
IN
– 1)
10µF 10µF
V
d
1N4148
V
d
1N4148
1144 F09
LTC1144
1
2
3
4
8
7
6
5
+
+
C2
10µF
C1
10µF
V
+
4V TO 36V
1144 F10
LTC1144
±0.002%
T
MIN
≤ T
A
≤ T
MAX
I
L
≤ 100nA
V+
2
1
2
3
4
8
7
6
5
+
+
C2
10µF
C1
10µF
OUTPUT
COMMON
V
B
/2
9V
–V
B
/2
–9V
1144 F11
LTC1144
V
B
18V
+
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