u

2

D _ CIN

RMS _ CIN

ESR _ CIN

P

I

R

OUT

IN

OUT

RMS _ CIN

OUT

IN

V

(V

V

)

I

I

V

u

u

u

RIPPLE

ROUT

RIPPLE

COUT

COUT

S

OUT

I

V

I

ESR

and V

8 F

C

2

2

OUT-RIPPLE-PP

ROUT

COUT

V

V

V

32

LM10504

SNVS739F – DECEMBER 2011 – REVISED OCTOBER 2016

www.ti.com

Product Folder Links: LM10504

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Copyright © 2011–2016, Texas Instruments Incorporated

Output ripple can be estimated from the vector sum of the reactive (capacitance) voltage component and the real

(ESR) voltage component of the output capacitor with Equation 5 and Equation 6.

where

(5)

•

VOUT-RIPPLE-PP is the estimated output ripple

•

VROUT is the estimated real output ripple

•

VCOUT is the estimated reactive output ripple

(6)

The device is designed to be used with ceramic capacitors on the outputs of the buck regulators. The

recommended dielectric type of these capacitors is X5R, X7R, or of comparable material to maintain proper

tolerances over voltage and temperature. The recommended value for the output capacitors is 22 μF, 6.3 V with

an ESR of 2 mΩ or less. The output capacitors need to be mounted as close as possible to the output or ground

pins of the device.

Table 7. Recommended Output Capacitors

MODEL

TYPE VENDOR

VENDOR

VOLTAGE RATING

CASE SIZE

08056D226MAT2A

Ceramic, X5R

AVX Corporation

6.3 V

0805, (2012)

C0805L226M9PACTU

Ceramic, X5R

Kemet

6.3 V

0805, (2012)

ECJ-2FB0J226M

Ceramic, X5R

Panasonic - ECG

6.3 V

0805, (2012)

JMK212BJ226MG-T

Ceramic, X5R

Taiyo Yuden

6.3 V

0603, (1608)

C2012X5R0J226M

Ceramic, X5R

TDK Corporation

6.3 V

0603, (1608)

8.2.2.1.3.2

Input Capacitor Selection

There are 3 buck regulators in the LM10504 device. Each of these buck regulators has its own input capacitor

which must be located as close as possible to their corresponding SWx_VIN and SWx_GND pins, where x

designates Buck 1, 2, or 3. The 3 buck regulators operate at 120° out of phase, which means that they switch on

at equally spaced intervals, to reduce the input power rail ripple. TI recommends connecting all the supply and

ground pins of the buck regulators, SWx_VIN to two solid internal planes located under the device. In this way,

the 3 input capacitors work together and further reduce the input current ripple. A larger tantalum capacitor can

also be located in the proximity of the device.

The input capacitor supplies the AC switching current drawn from the switching action of the internal power

FETs. The input current of a buck converter is discontinuous, so the ripple current supplied by the input capacitor

is large. The input capacitor must be rated to handle both the RMS current and the dissipated power.

The input capacitor must be rated to handle this current with Equation 7.

(7)

The power dissipated in the input capacitor is given by Equation 8.

(8)

The device is designed to be used with ceramic capacitors on the inputs of the buck regulators. The

recommended dielectric type of these capacitors is X5R, X7R, or of comparable material to maintain proper

tolerances over voltage and temperature. The minimum recommended value for the input capacitor is 10 µF with

an ESR of 10 mΩ or less. The input capacitors need to be mounted as close as possible to the power and

ground input pins of the device.

The input power source supplies the average current continuously. However, during the PFET switch on-time,

the demanded di/dt is higher than can be typically supplied by the input power source. This delta is supplied by

the input capacitor.