LT1026 Datasheet, PDF (4/8 Pages) Linear Technology – Voltage Converter

LT1026
APPLICATIONS INFORMATION
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.
TYPICAL APPLICATIONS
–V_OUT
Positive to Negative Converter
1µF
1µF
1 _C1–
8
+V_OUT
NC
2 _C2+
C1^{+ 7}
3 _C2–
LT1026
6
V_IN
V_IN
4 _–VOUT
5
GND
1026 • TA03
4
Voltage Doubler
1µF
1 _C1–
8
+V_OUT
2 _C2+
C1^{+ 7}
3 _C2–
LT1026
6
V_IN
V_IN
4 _–VOUT
5
GND
V_OUT
1µF
1026 • TA04