SC810EVB datasheet(17/20 Pages) SEMTECH

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SC810

or the fast-charge current limit value, depending on the

voltage at the output.

Operation Without a Battery

The SC810 can be operated as a 4.2V LDO regulator

without the battery present, for example, for factory

testing. If this use is anticipated, the total output capaci-

tance, C

BAT

plus any other capacitors tied directly to BAT

pin network, should be at least 2.2μF but less than 22μF to

ensure stability in CV regulation. To operate the charger

without a battery, the ENB pin must be driven low or

grounded. The output current is limited by the pro-

grammed fast-charge current. The charger should not be

disabled (V

ENB

> V

) without a battery present.

Dynamically Selectable Charge Current

The IPRGM resistance can be altered dynamically under

processor control by switching a second IPRGM pin resis-

tor. When the higher current is required, the switch is

turned on, making the effective programming resistance

equal to the parallel combination of the two resistors. The

external circuit is illustrated in Figure 6.

IPRGM

RIPRGM

RIPRGM_HI

Hi/Lo

Current Select

Figure 6 — Dynamic selection of low and high charge

currents.

Note that the IPRGM pin resistor programs the fast-charge,

pre-charge, and termination currents, so all will be modi-

fied by a change in the IPRGM pin resistor.

An open-drain GPIO can be used directly to engage the

parallel resistor R

IPRGM_HI

. Care must be taken to ensure that

the R

DS-ON

of the GPIO is considered in the selection of

IPRGM_HI

. Also important is the part-to-part and tempera-

ture variation of the GPIO R

DS-ON

, and their contribution to

the High Current charge current tolerance. Note also that

IPRGM will be pulled up briefly to as high as 3V during

startup to check for an IPRGM static pinshort to ground. A

small amount of current could, potentially, flow from

IPRGM into the GPIO ESD structure through R

IPRGM_HI

during

this event. While unlikely to do any harm, this effect must

also be considered.

USB Dedicated Charger Compatibility

The SC810 is well suited to the USB Charging Specification,

Revision 1.0, Dedicated Charger, Sections 3.5 and 4.1, due

to thermal limiting and its current-limited-supply charg-

ing behavior.

The USB Dedicated Charger is required to limit its output

current to more than 0.5A and less than 1.5A. A dedicated

charger identifies itself by shorting together the USB D+

and D- lines. Once the dedicated charger is detected, the

SC810, with its 1A maximum programmed fast charge

current, permits the fast-charge current to be set higher

than the 500mA USB High Power Mode specified limit to

permit faster charging of a large battery. (See the section

Dynamically Selectable Charge Current.)

If the USB Dedicated Charger’s current limit exceeds the

SC810 programmed fast-charge current, then its output

will regulate to 5V, and the fast-charge current will be

determined by the SC810 IPRGM pin resistance to ground.

If the resulting power dissipation in the SC810 causes an

excessive rise in temperature, then thermal limiting will

reduce the charge current as needed to ensure safe charg-

ing. But if the USB Dedicated charger’s current limit is less

than the SC810 programmed fast-charge current, then its

output voltage will be pulled down to the battery voltage

plus charging path dropout. (The USB Dedicated Charger

is required to maintain its current limit down to 2V.) This

behavior is recognized in the USB Battery Charging

Specification, Section 3.5, as an accepted means to reduce

power dissipation in the charging circuit while charging at

high current.

The SC810 thermal limiting and current-limited-adapter

charging capability together ensure reliable charging at

any programmed charge current, using any USB Battery

Charging Specification compliant Dedicated Charger,

regardless of its current limit.

External Power Path Management

Some applications require that the battery be isolated

from the load while charging. Figure 7 illustrates a typical

charger bypass circuit. This circuit powers the load directly

from the charging source via the Schottky diode D

BYPASS

Applications Information (continued)

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