TLVM13640 datasheet(16/43 Pages) TI2

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AGND

VOUT

FBT

FBB

10 kΩ

Figure 7-2. FB Resistor Divider

Table 7-1. Standard RFBT Values, Recommended FSW and Minimum COUT

VOUT (V)

RFBT (kΩ) (1)

RECOMMENDED

FSW (kHz)

COUT(MIN) (µF)

(EFFECTIVE)

VOUT (V)

RFBT (kΩ) (1)

RECOMMENDED

FSW (kHz)

COUT(MIN) (µF)

(EFFECTIVE)

1.0

Short

400

300

2.5

750

1.2

500

200

3.0

750

1.5

4.99

500

160

3.3

23.2

800

1.8

8.06

600

120

5.0

40.2

1000

2.0

600

100

6.0

49.9

1000

(1)

RFBB = 10 kΩ.

Note that higher feedback resistances consume less DC current, which is mandatory if light-load efficiency is

critical. However, RFBT larger than 1 MΩ is not recommended as the feedback path becomes more susceptible

to noise. High feedback resistance generally requires more careful layout of the feedback path. It is important to

keep the feedback trace as short as possible while keeping the feedback trace away from the noisy area of the

PCB. For more layout recommendations, see Section 10.

7.3.3 Input Capacitors

Input capacitors are necessary to limit the input ripple voltage to the module due to switching-frequency AC

currents. TI recommends using ceramic capacitors to provide low impedance and high RMS current rating over

a wide temperature range. Equation 2 gives the input capacitor RMS current. The highest input capacitor RMS

current occurs at D = 0.5, at which point the RMS current rating of the capacitors should be greater than half the

output current.

CIN,rms

OUT

1 D

(2)

where

• D = VOUT / VIN = the module duty cycle

Ideally, the DC and AC components of input current to the buck stage are provided by the input voltage source

and the input capacitors, respectively. Neglecting inductor ripple current, the input capacitors source current of

amplitude (IOUT – IIN) during the D interval and sink IIN during the 1 – D interval. Thus, the input capacitors

conduct a square-wave current of peak-to-peak amplitude equal to the output current. The resultant capacitive

component of AC ripple voltage is a triangular waveform. Together with the ESR-related ripple component,

Equation 3 gives the peak-to-peak ripple voltage amplitude:

TLVM13630

SLVSFT6B – MAY 2021 – REVISED JANUARY 2022

www.ti.com

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