IL2595-xx
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 V
IN
= 13V
Regulator stops switching at V
IN
= 8V
FIGURE 5. Undervoltage Lockout with Hysteresis for Inverting Regulator
FIGURE 6. Inverting
−5V
Regulator with Delayed Startup
FIGURE 7. Inverting Regulator Typical Load Current
Because of differences in the operation of the inverting regulator, the standard design procedure is not used to select the
inductor value. In the majority of designs, a 68 µH, 1.5A inductor is the best choice. Capacitor selection can also be
narrowed down to just a few values. Using the values shown in Figure 6 will provide good results in the majority of
inverting designs.
This type of inverting regulator can require relatively large amounts of input current when starting up, even with light loads.
Input currents as high as the IL2595 current limit (approx 1.5A) are needed for at least 2 ms or more, until the output
reaches its nominal output voltage. The actual time depends on the output voltage and the size of the output capacitor.
Rev. 00 8
IKSEMICON [ IK SEMICON CO., LTD ]
