LM2575T-15 datasheet(22/44 Pages) TI1

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LM2575-12

1N5817

COUT

1000 PF

Feedback

Output

VIN

CIN

100 PF

GND

150 PH

VOUT = -12V

-VIN

-5V to -12V

Low ESR

ON/OFF

LM1575, LM2575-N, LM2575HV

SNVS106E – MAY 1999 – REVISED APRIL 2013

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Typical Load Current

200 mA for VIN = −5.2V

500 mA for VIN = −7V

Pin numbers are for TO-220 package.

Figure 33. Negative Boost

UNDERVOLTAGE LOCKOUT

In some applications it is desirable to keep the regulator off until the input voltage reaches a certain threshold. An

undervoltage lockout circuit which accomplishes this task is shown in Figure 34, while Figure 35 shows the same

circuit applied to a buck-boost configuration. These circuits keep the regulator off until the input voltage reaches

a predetermined level.

VTH ≈ VZ1 + 2VBE (Q1)

(16)

DELAYED STARTUP

The ON /OFF pin can be used to provide a delayed startup feature as shown in Figure 36. With an input voltage

of 20V and for the part values shown, the circuit provides approximately 10 ms of delay time before the circuit

begins switching. Increasing the RC time constant can provide longer delay times. But excessively large RC time

constants can cause problems with input voltages that are high in 60 Hz or 120 Hz ripple, by coupling the ripple

into the ON /OFF pin.

ADJUSTABLE OUTPUT, LOW-RIPPLE

POWER SUPPLY

A 1A power supply that features an adjustable output voltage is shown in Figure 37. An additional L-C filter that

reduces the output ripple by a factor of 10 or more is included in this circuit.

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Product Folder Links: LM1575 LM2575-N LM2575HV

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