SC803 datasheet(8/17 Pages) SEMTECH

8 / 17 page

 2004 Semtech Corp.

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SC803

POWER MANAGEMENT

Applications Information (Cont.)

Using the SC803 With a Charge Controller IC

The SC803 can also be used with numerous charge con-

troller ICs on the market. In many instances the charge

controller will control the charging and termination of the

SC803. The best method of interfacing the SC803 with

such a device is to place the SC803 in LDO mode, and

monitor the current to the battery by an ADC that

samples the voltage on the IPRGM pin. Slow and fast

charge can be controlled by placing two resistors in se-

ries from IPRGM to GND and adding a transistor switch

across one of the resistors. This way the current can be

monitored for proper termination by the charge control-

ler. In LDO mode the STAT LED will not light. When charg-

ing the battery in LDO mode the charge profile will be the

same as in charge mode except there will be no precharge

or termination current function. Meanwhile, the maxi-

mum current the battery will see is set by the battery

equivalent circuit or the fast-charge current limit. The

battery will still charge in this mode, albeit a slightly dif-

ferent approach than placing the charger in the charge

mode.

Evaluation Board

The evaluation board is shown on Page 10. The evalua-

tion board was designed to test the complete operation

of the SC803. Note the minimum parts requirement is

shown within the dotted rectangle on the schematic. The

adaptor voltage of 5V is applied to TP1 and TP2 which

supplies power to the SC803. The output charger volt-

age or LDO output voltage is taken off of TP4 and TP5.

Jumper JP5 will set the device in LDO mode when in-

serted or charge mode when left open. Jumper JP6 will

enable the device when inserted or disable the device

when left open. Note as long as power is applied to VCC

the CP LED will light, regardless of the EN pin level. Jumper

JP4 is used to measure the bias current of the SC803

and should always be in place except when measuring

bias current. JP1 and JP3 set the charge limit voltage to

4.2V or 4.1V respectively. Only one of these jumpers JP1

or JP3 should be in place at any given time. If you expect

VCC to exceed 6V (testing breakdown of the SC803) and

you want to set the output voltage to 4.2V you should

remove any jumper on JP1 and manually tie pin 2 of JP1

to the CP pin, because the absolute maximum voltage

on the VPRGM input pin is 6V. Jumper JP7 when inserted

will short the BSEN line to Vout for charging Lithium-Ion

batteries. Jumper JP2 should be inserted when an ad-

justable voltage is required, with the addition of R1, R2

& C2. For more information about selection of an ad-

justable voltage see the section titled, Configuring the

Output Voltage to the Battery. Note, only one of these

jumpers JP2 or JP7 should be inserted at any given time.

Jumper JP8 should be left open and is used only for test-

ing SC801M operation. Connector J1 is used for con-

necting the evaluation board to a demonstration plat-

form to exemplify the SC803 operation. Other compo-

nents on the eval board consist of Semtech’s SD12 and

SD05 ESD clamp diodes which should be part of any

system requiring ESD protection. LED’s for status infor-

mation and TP3 which will allow the current through the

battery to be monitored. The input capacitor C1 is cho-

sen to be 10uF to decouple any inductance from a labo-

ratory supply when evaluation is taking place.

Complete Charge Cycle

The complete charge cycle of the SC803 is shown on

page 15. The pre-charge current will be under control

until the precharge threshold of 2.8V is reached. At this

time the device enters the fast-charge mode and the

output voltage continues to increase as the constant

current is applied to the battery. Eventually constant volt-

age is reached and the current begins to decrease until

the termination current threshold is reached at which

time the SC803 will turn off. Many Lithium-Ion batteries

have a built in under-voltage detect circuit. This makes

the battery pack open circuited when the battery volt-

age falls below 3V typically. With these batteries the

SC803 will unlikely enter pre-charge operation because

the battery voltage will always be above 2.8V.

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