4
LT1026
1026fb
APPLICATIONS INFORMATION
UWUU
The LT1026 is a nonregulating voltage converter that
converts a single input voltage into both a positive and
negative output at up to 15mA. A positive input voltage is
first doubled and then the doubled voltage is inverted. The
voltage output level is dependent on both the input voltage
and the output loading. The total output current available
depends on the individual loading of the outputs since
loading on one output affects the load and the voltage of
the other.
Only four external components are needed for operation.
Two charge pump capacitors and two output storage
capacitors. Nominal value for these capacitors is 1µF, but
the LT1026 will operate (with reduced performance) down
to 0.1µF. Higher value capacitors (22µF) will reduce ripple
and slightly lower output impedance. For higher output
currents the outputs of several converters may be paral-
leled with common output capacitors.
The substrate diodes are an inherent part of the IC, and
must always be reversed biased to isolate the individual
transistors. In the LT1026 the substrate is tied to the
negative output. If the negative output is not used, such as
when only the voltage doubler output is needed, –V
OUT
must be tied to ground so the substrate diodes are
properly biased. The substrate diodes must never become
forward biased even during overload conditions. For ex-
ample, pulling –V
OUT
positive with respect to ground can
forward bias the substrate diodes. Clamping the substrate
to ground with an external diode would be needed to
ensure proper operation and prevent the substrate from
carrying any current.
No overload protection is included on the LT1026. Neither
output is damaged by momentary shorts, but during
sustained shorts the resulting high current flow will over-
heat the IC.
Ripple Output Voltage vs Temperature
OUTPUT CAPACITOR (µF)
1.0
0
RIPPLE (mV
P-P
)
10
20
30
40
60
2.2
4.7 10 22
1026 • TPC07
47 100
50
V
IN
= 5V
I
L
= 5mV
BOTH OUTPUTS
TEMPERATURE (°C)
–50
–10
OUTPUT VOLTAGE (V)
–8
–4
–2
0
10
4
0
50
75
LT1026 • TPC08
–6
6
8
2
–25
25
100
125
C = 22µF
V
IN
= 5V
I
L
= 1mA
TYPICAL PERFORMANCE CHARACTERISTICS
UW
