SC802 SEMTECH [Semtech Corporation], SC802 Datasheet - Page 10

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

Configuring the Output Voltage to the Battery
Fixed Mode
The battery voltage is set by the VPRGM pin in fixed mode
and externally in adjust mode. If VPRGM is logic high the
output voltage is set to 4.2V. If this pin is logic low the
output voltage will be set to 4.1V. For a value other than
4.1V or 4.2V a resistor divider is required.
Adjust Mode
When the SC802 is configured with an output voltage
other than 4.1 or 4.2V it is operating in adjust mode. In
adjust mode the output voltage is set by an external re-
sistor divider. The SC802 provides the ability to discon-
nect the external feedback resistor divider when the
battery is not being charged to reduce current drain from
the battery in normal operation. Connect the external
resistor divider between the VOUT pin and the VPRGM
pin with the divider tap connected to the BSEN pin to
utilize this feature. The SC802 adjust mode schematic is
shown above. The equation for setting the output
voltage is:
The capacitor across R4 in the feedback networks intro-
duces zero-pole frequency compensation for stability.
Place the zero according to the following equation to in-
sure stability.
When the SC802 is in Adjust mode the VCC is required
to be 150mV > Vout. Internal protection circuits will dis-
able the output if VOUT approaches VCC.
© 2005 Semtech Corp.
POWER MANAGEMENT
nary
CHARGER VIN
C1
1uF
R4
Prelimi-
VOUT
×
C1
THERMISTOR
=
t
RT1
=
R5
2
π
⎛
⎜
⎝
1
×
+
100
1
R4
R3
R1
kHz
⎞
⎟
⎠
×
R2
Adjust Mode Schematic
3.0
14
13
ADC Iset
3
7
4
8
6
5
VCC
VCC
IPRGM
EN/NTC
ITERM
BIPB
GND
RFGND
SC802
CHRGB
VPRGM
BSEN
VOUT
VOUT
RTIM
CPB
AFC
10
BATTERY
11
10
12
2
1
16
15
9
Capacitor Selection
Input and output capacitors can be low cost ceramic type.
The output capacitance range is 1uF to 4.7uF. The input
capacitor is typically between 0.1uF to 1uF but larger
values will not degrade performance.
Overcurrent and Max Temperature Protection
Overcurrent protection is inherent in all modes of opera-
tion. When the device is in charge-mode (BIPB=low) the
output is current limited to either the pre-charge current
limit value or the fast charge current limit value depend-
ing on the voltage at the output. When the device is in
LDO mode (BIPB=high) the output current is limited to
the fast charge current limit. Max die temperature pro-
tection is included on the SC802. This feature allows
the SC802 to operate with maximum power dissipation
by disabling the output current when the die tempera-
ture reaches OT. The result is that the SC802 will oper-
ate as a pulse charger in extreme power dissipation ap-
plications delivering the maximum allowable output cur-
rent while regulating the internal die temperature to a
safe level.
Remote Kelvin Sensing at the Battery
Kelvin sensing of both the positive and negative termi-
nals of the battery is possible with the SC802. The BSEN
pin provides the positive sensing voltage feedback to
the CV amplifier and should be connected as close to
the battery + terminal as possible. Likewise the REFGND
pin should be kelvin connected to the negative terminal
of the battery. This allows the designer great flexibility in
PCB layout and achieves a much greater accuracy in sens-
ing the battery voltage where it counts, at the battery
terminals! Therefore, when laying out the PCB the de-
signer should route the BSEN pin directly to the terminal
at which the battery gets connected. In the LDO mode,
the BSEN pin will still need to sense the output voltage;
therefore BSEN should never be left floating. . . . .
C2
2.2uF
R4
R3
C1
SC802/SC802A
R6
CHARGE
R7
1K
www.semtech.com
CHARGER
PRESENT
R8
1K