LM2595 datasheet(12/43 Pages) TI1

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LM2595

SNVS122C – MAY 1999 – REVISED MAY 2016

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Feature Description (continued)

This example uses the LM2595 5-V version to generate a

−5-V output, but other output voltages are possible by

selecting other output voltage versions, including the adjustable version.

Because 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. Figure 19 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 40 V. For example, when converting 20 V to

−12 V, the regulator would see

32 V between the input pin and ground pin. The LM2595 has a maximum input voltage spec of 40 V.

Additional diodes are required in this regulator configuration. Diode D1 is used to isolate input voltage ripple or

noise from coupling through the CIN capacitor to the output, under light or no load conditions. Also, this diode

isolation changes the topology to closely resemble a buck configuration thus providing good closed loop stability.

TI recommends a Schottky diode 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 CIN 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 = 13 V

Regulator stops switching at VIN = 8 V

Figure 17. Undervoltage Lockout With Hysteresis For Inverting Regulator

CIN – 220-μF, 25-V tantalum Sprague 595D

120-μF, 50-V electrolytic Panasonic HFQ

COUT – 22-μF, 20-V tantalum Sprague 595D

120-μF, 25-V electrolytic Panasonic HFQ

Figure 18. Inverting

−5-V Regulator With Delayed Start-Up

LM2595 Datasheet(PDF) 12 Page - Texas Instruments