TPS65721 datasheet(45/50 Pages) TI

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Vout

Vin

Vout = Vout

+ ESR

Cout

´ ç

´ ¦

SET

CHARGE

SET

TPS65720

TPS65721

www.ti.com

SLVS979 – OCTOBER 2009

(5)

Where the highest output voltage ripple occurs at the highest input voltage Vin.

At light load currents the converter operates in Power Save Mode and the output voltage ripple is dependent on

the output capacitor value. The output voltage ripple is set by the internal comparator delay and the external

capacitor. The typical output voltage ripple is less than 1% of the nominal output voltage.

Input Capacitor Selection

Because of the nature of the buck converter having a pulsating input current, a low ESR input capacitor is

required for best input voltage filtering and minimizing the interference with other circuits caused by high input

voltage spikes. The converters need a ceramic input capacitor of 4.7

μF. The input capacitor can be increased

without any limit for better input voltage filtering.

Table 2. Tested Capacitors

TYPE

VALUE

VOLTAGE RATING

SIZE

SUPPLIER

MATERIAL

GRM155R60G475ME47D

4.7

μF

4 V

0402

Murata

Ceramic X5R

GRM155R60J225ME15D

2.2

μF

6.3 V

0402

Murata

Ceramic X5R

GRM188R60J475K

4.7

μF

6.3 V

0603

Murata

Ceramic X5R

GMK107BJ105K

μF

35 V

0603

Taiyo Yuden

Ceramic X5R

CHARGER/POWER PATH

Charger Stability

In order to ensure stable operation of the charger including the power path, a list of components and their

recommended value is given below. Note that these values represent the capacitance or inductance value in the

application under the given operating conditions. For example, ceramic capacitors will typically show a drop in

capacitance when a dc voltage is applied. Due to this dc bias effect, the capacitance in the applications when

voltage is applied is much less than the nominal capacitor value. See the manufacturers data sheet on this.

At pin AC, a series inductance of may be used with a values as stated below.

Pins AC, SYS and BAT have been tested to be stable with the values given in the table:

PIN NAME

Cmin (

μF)

Cmax (

μF)

Lmin (

μH)

lmax (

μH)

0.1

SYS

–

BAT

0.1

4.7

–

Setting the Charge Current

The charge current is set with an external resistor connected form ISET to GND.

The resulting charge current is:

(6)

Additionally, the charge current can be scaled to 100%, 75%, 50% or 25% of the value set by Rset by software in

Dynamic Power Path Management (DPPM)

The charger/power path in TPS6572x contains two different features to ensure there is sufficient power at the

load and the input voltage supplying the charger/power path does not collapse.

First there is output voltage DPPM, which is a control loop to keep the voltage at the output of the power path

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