SC802 SEMTECH [Semtech Corporation], SC802 Datasheet - Page 7

• Manufacturer Part Number: SC802
• Description: Fully Integrated Lithium-Ion Battery Charger System with Timer
• Manufacturer: SEMTECH [Semtech Corporation]

General Operation
The SC802 is configured based on the application for
Fast Charge and Termination current, output voltage, tim-
ing requirements, and operation with and without a bat-
tery (ldo mode). A typical charging cycle is described be-
low. Details on alternate applications and output pro-
grammability are covered in the individual sections.
The charging cycle begins when the adapter is plugged
in. The SC802 performs glitch filtering on the VCC input
and initiates a charge cycle when VCC > UVLO. At this
time, the CPB and CHRGB signals are active turning on
the charger LED’s. If the battery voltage is less than
2.8V, the SC802 will charge the output with the pre-
charge current. When the battery voltage exceeds 2.8V,
the SC802 enters fast-charge or constant current (CC)
mode. When the battery voltage reaches its final value,
the charger enters the constant voltage (CV) mode. In
this mode the output current decreases as the battery
continues to charge until the termination current level is
reached.
The CHRGB led turns off when Iout is less than
Itermination but the SC802 continues to hold the bat-
tery in CV charge mode until the timer expires. At this
point the charger enters the monitor mode where the
output remains off until Vout drops by 100mV and a new
charge cycle is initiated.
Pre-Charge Mode
Pre-charge mode is automatically enabled whenever the
battery voltage is below 2.8V. It is used to limit the power
dissipation and precondition the battery for fast charg-
ing. The pre-charge current value is selected by the re-
sistor on the ITERM pin. The pre-charge current is pro-
grammable from 10mA to 125mA on the SC802 and up
to 150mA on the SC802A. The equation to select the
pre-charge current is different for the two part types and
given by:
If the charge timer is in use there is also a maximum
allowed pre-charge duration. If the pre-charge time ex-
© 2005 Semtech Corp.
POWER MANAGEMENT
PRELIMINARY
Applications Information
SC802A
SC802
:
:
PCI
PCI
=
=
⎛
⎜ ⎜
⎝
⎛
⎜ ⎜
⎝
R
R
2.8
TERM
1.5
TERM
⎞
⎟ ⎟
⎠
⎞
⎟ ⎟
⎠
×
×
88
97
7
ceeds 1/4 of the total charge cycle the charger will turn
off due to a pre-charge fault. This fault is cleared when
EN or VCC is toggled or the output voltage rises above
2.8V.
Fast-Charge Mode (CC)
The fast-charge or CC mode is active when the battery
voltage is above 2.8V and less than the CV or final float
charge voltage of the battery. The fast-charge current
can be set to a maximum of 1.0A and is selected by the
program resistor on the IPRGM pin. The voltage on this
pin will represent the current through the battery enabling
a microprocessor via an analog-to-digital converter (ADC)
to monitor battery current by sensing the voltage on the
IPRGM pin. The equation to set the fast-charge current
is given by:
Note that for a given program resistor the current through
the battery in CV mode can be determined by replacing
1.5 with the actual voltage on the IPRGM pin in the above
equation. The CC current can also be modified by apply-
ing an analog voltage to the AFC pin as described below.
Analog Fast Charge (AFC Pin)
Many applications require more than one current setting
for Fast Charge. This feature is included in the SC802
by using the AFC function. When the AFC pin is con-
nected to VCC the device behaves as described in the
previous section. When the AFC pin is driven by and
analog voltage between 0 and 1.5V the SC802 auto-
matically uses this pin voltage to set the maximum fast-
charge current setting according to the following equa-
tion.
SC802A
SC802A
SC802
SC802
:
:
:
AFCI
FCI
AFCI
:
FCI
=
=
⎛
⎜ ⎜
⎝
=
=
R
⎛
⎜ ⎜
⎝
R
1.5
⎛
⎜ ⎜
⎝
⎛
⎜ ⎜
⎝
PRGM
SC802/SC802A
V
R
R
PROG
AFC
V
1.5
PRGM
PROG
AFC
⎞
⎟ ⎟
⎠
⎞
⎟ ⎟
⎠
×
×
1000
⎞
⎟ ⎟
⎠
⎞
⎟ ⎟
⎠
1000
×
×
1000
1000
-
-
0.3
www.semtech.com
0.3
×
×
Iterm
Iterm