SC801 datasheet(8/17 Pages) SEMTECH

8 / 17 page

 2002 Semtech Corp.

www.semtech.com

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POWER MANAGEMENT

Applications Information (Cont.)

Using the SC801 With a Charge Controller IC

The SC801 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

SC801. The best method of interfacing the SC801 with

such a device is to place the SC801 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 SC801 and the SC801M. 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 SC801. The output

charger voltage or LDO output voltage is taken off of

TP4 and TP5. Jumper JP5 will set the device in LDO mode

when inserted 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 SC801 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 SC801) and you want to set the output voltage to

4.2V you should remove any jumper on JP1 and manu-

ally 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 in-

serted when an adjustable voltage is required, with the

addition of R1, R2 & C2. For more information about

selection of an adjustable 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 testing SC801M operation. Connector J1

is used for connecting the evaluation board to a demon-

stration platform to exemplify the SC801 operation. Other

components on the eval board consist of Semtechs

SD12 and SD05 ESD clamp diodes which should be part

of any system requiring ESD protection. LEDs for status

information and TP3 which will allow the current through

the battery to be monitored. The input capacitor C1 is

chosen to be 10uF to decouple any inductance from a

laboratory supply when evaluation is taking place.

Complete Charge Cycle

The complete charge cycle of the SC801 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 SC801 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

SC801 will unlikely enter pre-charge operation because

the battery voltage will always be above 2.8V.

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