TL2575 datasheet(15/34 Pages) TI1

15 / 34 page

TL2575, TL2575HV

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SLVS638C – JANUARY 2006 – REVISED NOVEMBER 2014

Typical Application (continued)

10.1.2.5 Output Voltage Ripple and Transients

As with any switching power supply, the output of the TL2575 and TL2575HV devices have 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 current and the ESR of the output capacitor (see Output Capacitor (COUT)). Furthermore,

the output also may contain small voltage spikes at the peaks of the sawtooth waveform. This is due to the fast

switching of the output switch and the parasitic inductance of COUT. These voltage spikes can be minimized

through the use of low-inductance capacitors.

There are several ways to reduce the output ripple voltage: a larger inductor, a larger COUT, or both. Another

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 11).

10.1.2.6 Grounding

The power and ground connections of the TL2575 and TL2575HV devices must be low impedance to help

maintain output stability. For the 5-pin packages, both pin 3 and tab are ground, and either connection can be

used as they are both part of the same lead frame. 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.

10.1.2.7 Reverse Current Considerations

There is an internal diode from the output to VIN. Therefore, the device does not protect against reverse current

and care must be taken to limit current in this scenario.

10.1.2.8 Buck Regulator Design Procedure

PROCEDURE (Fixed Output)

EXAMPLE (Fixed Output)

Known:

VOUT = 3.3 V, 5 V, 12 V, or 15 V

VOUT = 5 V

VIN(Max) = Maximum input voltage

VIN(Max) = 20 V

ILOAD(Max) = Maximum load current

ILOAD(Max) = 1 A

1. Inductor Selection (L1)

A. From Figure 13 through Figure 16, select the appropriate inductor A. From Figure 14 (TL2575-05), the intersection of 20-V line and 1-A

code based on the intersection of VIN(Max) and ILOAD(Max).

line gives an inductor code of L330.

B. The inductor chosen should be rated for operation at 52-kHz and B. L330

→ L1 = 330 μH

have a current rating of at least 1.15 × ILOAD(Max) to allow for the Choose from:

ripple current. The actual peak current in L1 (in normal operation)

34042 (Schott)

can be calculated as follows:

PE-52627 (Pulse Engineering)

IL1(pk) = ILOAD(Max) + (VIN – VOUT) × ton / 2L1

Where ton = VOUT / VIN × (1 / fosc)

RL1952 (Renco)

2. Output Capacitor Selection (COUT)

A. The TL2575 control loop has a two-pole two-zero frequency A. COUT = 100-μF to 470-μF, standard aluminum electrolytic

response. The dominant pole-zero pair is established by COUT and

L1. To meet stability requirements while maintaining an acceptable

output ripple voltage (Vripple ≉ 0.01 × VOUT), the recommended range

for a standard aluminum electrolytic COUT is between 100 μF and

470

μF.

B. COUT should have a voltage rating of at least 1.5 × VOUT. But if a B. Although a COUT rated at 8 V is sufficient for VOUT = 5 V, a

low output ripple voltage is desired, choose capacitors with a higher- higher-voltage capacitor is chosen for its typically lower ESR (and

voltage ratings than the minimum required, due to their typically hence

lower

output

ripple

voltage)

→

Capacitor

voltage

lower ESRs.

rating = 20 V.

3. Catch Diode Selection (D1) (see Table 1)

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