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-
2004 Semtech Corp.
8
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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