IL2596-xx
This example uses the IL2596-5.0 to generate a
−5V
output, but other output voltages are possible by selecting other
output voltage versions, including the adjustable version. Since this regulator topology can produce an output voltage that is
either greater than or less than the input voltage, the maximum output current greatly depends on both the input and output
voltage. The curve shown in Figure 8 provides a guide as to the amount of output load current possible for the different input
and output voltage conditions.
The maximum voltage appearing across the regulator is the absolute sum of the input and output voltage, and this must
be limited to a maximum of 40V. For example, when converting +20V to
−12V,
the regulator would see 32V between the input
pin and ground pin. The IL2596 has a maximum input voltage spec of 40V.
Additional diodes are required in this regulator configuration. Diode D1 is used to isolate input voltage ripple or noise
from coupling through the C
IN
capacitor to the output, under light or no load conditions. Also, this diode isolation changes the
topology to closley resemble a buck configuration thus providing good closed loop stability. A Schottky diode is recommended
for low input voltages, (because of its lower voltage drop) but for higher input voltages, a fast recovery diode could be used.
Without diode D3, when the input voltage is first applied, the charging current of C
IN
can pull the output positive by
several volts for a short period of time. Adding D3 prevents the output from going positive by more than a diode voltage.
This circuit has hysteresis
Regulator starts switching at VIN = 13V
Regulator stops switching at VIN = 8V
Figure 6. Undervoltage Lockout with Hysteresis for Inverting Regulator
CIN —68 µF/25V Tant. Sprague 595D
470 µF/50V Elec. Panasonic HFQ
COUT —47 µF/20V Tant. Sprague 595D
220 µF/25V Elec. Panasonic HFQ
Figure 7. Inverting
−5V
Regulator with Delayed Startup
Figure 8. Inverting Regulator Typical Load Current
Rev. 03 8
IKSEMICON [ IK SEMICON CO., LTD ]
