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Output Voltage Ripple and Transients

Feedback Connection

ON/OFF Input

Grounding

LM2575

1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR

SLVS569E – JANUARY 2005 – REVISED JANUARY 2006

APPLICATION INFORMATION (continued)

As with any switching power supply, the output of the LM2575 has a sawtooth-ripple voltage at the switching

frequency. Typically about 1% of the output voltage, this ripple is due mainly to the inductor sawtooth-ripple

voltage spikes at the peaks of the sawtooth waveform. This is due to the fast switching of the output switch and

capacitors.

method is to use a small LC filter (20

µH and 100 µF) at the output. This filter can reduce the output ripple

voltage by a factor of 10 (see Figure 1).

FEEDBACK must be connected between the two programming resistors. Again, both of these resistors should be

in close proximity to the regulator, and each should be less than 100 k

Ω to minimize noise pickup.

ON/OFF should be grounded or be a low-level TTL voltage (typically <1.6 V) for normal operation. To shut down

the LM2575 and put it in standby mode, a high-level TTL or CMOS voltage should be supplied to this pin.

The power and ground connections of the LM2575 must be low impedance to help maintain output stability. With

the 16-pin package, all the ground pins (including signal and power grounds) should be soldered directly to wide

PCB copper traces to ensure low-inductance connections and good thermal dissipation.

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