Datasheet

LM2594, LM2594HV
SNVS118C –DECEMBER 1999–REVISED APRIL 2013 www.ti.com
This circuit has an ON/OFF threshold of approximately 13V.
Figure 35. Undervoltage Lockout for Inverting Regulator
This circuit has hysteresis
Regulator starts switching at V
IN
= 13V
Regulator stops switching at V
IN
= 8V
Figure 36. Undervoltage Lockout with Hysteresis for Inverting Regulator
C
IN
— 68 μF/25V Tant. Sprague 595D
120 μF/35V Elec. Panasonic HFQ
C
OUT
— 22 μF/20V Tant. Sprague 595D
39 μF/16V Elec. Panasonic HFQ
Figure 37. Inverting −5V Regulator with Delayed Startup
This example uses the LM2594-5 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 38 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 LM2594 has a maximum input voltage spec of 40V (60V for the
LM2594HV).
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