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TL2575_10 Datasheet, PDF (17/29 Pages) Texas Instruments – 1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATORS
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TL2575, TL2575HV
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATORS
SLVS638B – MAY 2006 – REVISED JANUARY 2007
BUCK REGULATOR DESIGN PROCEDURE
PROCEDURE (Fixed Output)
EXAMPLE (Fixed Output)
Known:
VOUT = 3.3 V, 5 V, 12 V, or 15 V
VIN(Max) = Maximum input voltage
ILOAD(Max) = Maximum load current
1. Inductor Selection (L1)
Known:
VOUT = 5 V
VIN(Max) = 20 V
ILOAD(Max) = 1 A
1. Inductor Selection (L1)
A. From Figure 15 through Figure 18, select the appropriate inductor A. From Figure 16 (TL2575-05), the intersection of 20-V line and
code based on the intersection of VIN(Max) and ILOAD(Max).
1-A line gives an inductor code of L330.
B. From Table 2, choose the appropriate inductor based on the
inductor code. Parts from three well-known inductor manufacturers
are given. The inductor chosen should be rated for operation at
52-kHz and have a current rating of at least 1.15 × ILOAD(Max) to
allow for the ripple current. The actual peak current in L1 (in normal
operation) can be calculated as follows:
IL1(pk) = ILOAD(Max) + (VIN – VOUT) × ton/2L1
Where ton = VOUT/VIN× (1/fosc)
B. L330 → L1 = 330 µH
Choose from:
34042 (Schott)
PE-52627 (Pulse Engineering)
RL1952 (Renco)
2. Output Capacitor Selection (COUT)
2. Output Capacitor Selection (COUT)
A. The TL2575 control loop has a two-pole two-zero frequency
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.
A. COUT = 100-µF to 470-µF, standard aluminum electrolytic
B. COUT should have a voltage rating of at least 1.5 × VOUT. But if a
low output ripple voltage is desired, choose capacitors with a
higher-voltage ratings than the minimum required, due to their
typically lower ESRs.
B. Although a COUT rated at 8 V is sufficient for VOUT = 5 V, a
higher-voltage capacitor is chosen for its typically lower ESR (and
hence lower output ripple voltage) → Capacitor voltage
rating = 20 V.
3. Catch Diode Selection (D1) (see Table 1)
3. Catch Diode Selection (D1) (see Table 1)
A. In normal operation, the catch diode requires a current rating of
at least 1.2 × ILOAD(Max). For the most robust design, D1 should be
rated to handle a current equal to the TL2575 maximum switch peak
current; this represents the worst-case scenario of a continuous
short at VOUT.
A. Pick a diode with 3-A rating.
B. The diode requires a reverse voltage rating of at least
1.25 × VIN(Max).
B. Pick 30-V rated Schottky diode (1N5821, MBR330, 31QD03, or
SR303) or 100-V rated Fast Recovery diode (31DF1, MURD310, or
HER302).
4. Input Capacitor (CIN)
An aluminum electrolytic or tantalum capacitor is needed for input
bypassing. Locate CIN as close to the VIN and GND pins as
possible.
4. Input Capacitor (CIN)
CIN = 100 µF, 25 V, aluminum electrolytic
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