• Output voltage ripple

• Input voltage ripple

8.2.2.2 Output Voltage Resistors Selection

The output voltage is set with a resistor divider from the output node to the VFB pin. It is recommended to use

1% tolerance or better divider resistors. Start by using Equation 3 to calculate VOUT

To improve efficiency at very light loads consider using larger value resistors, too high of resistance will be more

susceptible to noise and voltage errors from the VFB input current will be more noticeable

OUT

R1

V

0.7651

0.0011

VOUT _ SET

1

R2

where VOUT _ SET is t arget VOUT voltage

§

·

u

u ¨

¸

©

¹

(3)

8.2.2.3 Output Filter Selection

The output filter used with the TPS54526 is an LC circuit. This LC filter has double pole at:

1

2

P

OUT

OUT

F

L

C

p

=

´

(4)

At low frequencies, the overall loop gain is set by the output set-point resistor divider network and the internal

gain of the TPS54526. 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 selected 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 8-2

Table 8-2. Recommended Component Values

Output Voltage (V)

R1 (kΩ)

R2 (kΩ)

C4 (pF)(1)

L1 (µH)

C8 + C9 (µF)

1

6.81

22.1

1.0 - 1.5

22 - 68

1.05

8.25

22.1

1.0 - 1.5

22 - 68

1.2

12.7

22.1

1.0 - 1.5

22 - 68

1.5

21.5

22.1

1.5

22 - 68

1.8

30.1

22.1

5 - 22

1.5

22 - 68

2.5

49.9

22.1

5 - 22

2.2

22 - 68

3.3

73.2

22.1

5 - 22

2.2

22 - 68

5

124

22.1

5 - 22

3.3

22 - 68

(1)

Optional

For higher output voltages at or above 1.8 V, additional phase boost can be achieved by adding a feed forward

capacitor (C4) in parallel with R1.

Since the DC gain is dependent on the output voltage, the required inductor value increases as the output

voltage increases. For higher output voltages above 1.8 V, additional phase boost can be achieved by adding a

feed forward capacitor (C4) in parallel with R1

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

fSW.

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TPS54526

SLVSB84D – MAY 2012 – REVISED APRIL 2021

Copyright © 2021 Texas Instruments Incorporated

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