4

LT1026

1026fb

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 1

µF, but

the LT1026 will operate (with reduced performance) down

to 0.1

µF. 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

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-

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

10

20

30

40

60

2.2

4.7

10

22

1026 • TPC07

47

100

50

BOTH OUTPUTS

TEMPERATURE (

°C)

–50

–10

–8

–4

–2

0

10

4

0

50

75

LT1026 • TPC08

–6

6

8

2

–25

25

100

125

C = 22

µF