TPS562210_15 Datasheet, PDF (15/34 Pages) Texas Instruments – TPS56x210, 4.5-V to 17-V Input, 2-A, 3-A Synchronous Step-Down Voltage Regulator In 8-Pin SOT-23

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TPS562210, TPS563210
SLVSCM6A – FEBRUARY 2015 – REVISED AUGUST 2015
At low frequencies, the overall loop gain is set by the output set-point resistor divider network and the internal
gain of the device. The low frequency phase is 180 degrees. At the output filter pole frequency, the gain rolls off
at a –40 dB per decade rate and the phase drops rapidly. D-CAP2™ introduces a high frequency zero that
reduces the gain roll off to –20 dB per decade and increases the phase to 90 degrees one decade above the
zero frequency. The inductor and capacitor for the output filter must be selected so that the double pole of
Equation 4 is located below the high frequency zero but close enough that the phase boost provided be the high
frequency zero provides adequate phase margin for a stable circuit. To meet this requirement use the values
recommended in Table 2.
Output Voltage (V)
1
1.05
1.2
1.5
1.8
2.5
3.3
5
6.5
Table 2. TPS562210 Recommended Component Values
R2 (kΩ)
3.09
3.74
5.76
9.53
13.7
22.6
33.2
54.9
75
R3 (kΩ)
10.0
10.0
10.0
10.0
10.0
10.0
10.0
10.0
10.0
L1 (µH)
MIN
TYP
MAX
1.5
2.2
4.7
1.5
2.2
4.7
1.5
2.2
4.7
1.5
2.2
4.7
1.5
2.2
4.7
2.2
3.3
4.7
2.2
3.3
4.7
3.3
4.7
4.7
3.3
4.7
4.7
C6 + C7 + C8 (µF)
20 - 68
20 - 68
20 - 68
20 - 68
20 - 68
20 - 68
20 - 68
20 - 68
20 - 68
The inductor peak-to-peak ripple current, peak current and RMS current are calculated using Equation 5,
Equation 6 and Equation 7. The inductor saturation current rating must be greater than the calculated peak
current and the RMS or heating current rating must be greater than the calculated RMS current.
Use 650 kHz for f_SW. Make sure the chosen inductor is rated for the peak current of Equation 6 and the RMS
current of Equation 7.
Il_P-P
=
V_OUT
V_IN(MAX)
´
V_IN(MAX) - V_OUT
L_O ´ ƒ_SW
(5)
Il_PEAK
= I_O
+ ^IlP-P
2
(6)
I_LO(RMS) =
I_O2
+
1
12
Il_P-P2
(7)
For this design example, the calculated peak current is 2.34 A and the calculated RMS current is 2.01 A. The
inductor used is a TDK CLF7045T-2R2N with a peak current rating of 5.5 A and an RMS current rating of 4.3 A.
The capacitor value and ESR determines the amount of output voltage ripple. The TPS562210 and TPS563210
are intended for use with ceramic or other low ESR capacitors. Recommended values range from 20µF to 68µF.
Use Equation 8 to determine the required RMS current rating for the output capacitor.
( ) _{ICO(RMS) =}
V_OUT ´ V_IN - V_OUT
12 ´ V_IN ´ L_O ´ ƒ_SW
(8)
For this design, two TDK C3216X5R0J226M 22 µF output capacitors are used. The typical ESR is 2 mΩ each.
The calculated RMS current is 0.286A and each output capacitor is rated for 4A.
9.2.1.2.3 Input Capacitor Selection
The TPS562210 and TPS563210 require an input decoupling capacitor and a bulk capacitor is needed
depending on the application. A ceramic capacitor over 10 µF is recommended for the decoupling capacitor. An
additional 0.1 µF capacitor (C3) from pin 3 to ground is optional to provide additional high frequency filtering. The
capacitor voltage rating needs to be greater than the maximum input voltage.
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