SC801
POWER MANAGEMENT
Applications Information (Cont.)
C 1
330pF
R 4
HIGH
R 3
LED FLAG
ON
OFF
IMPEDANCE
100K
59K
+5V
14
13
3
7
4
8
6
5
11
10
9
2
1
16
15
12
VC C
VC C
IPR GM
EN
ITER M
BIP
C P
STAT
OVP
VPR GM
BSEN
VOU T
VOU T
N C
POWER TO VCC
PINS
NO POWER TO
VCC PINS
X
CP
GN D
N C
C H AR G ER
VCC OVER-
VOLTAGE
VCC VOLTAGE
NORMAL
C 2
1uF
R 1
R 2
SC 801
F AU LT
STATU S
PR ESEN T
X
OVP
C 3
2.2uF
BATTER Y
BATTERY
BATTERY FULLY
CHARGED
LDO MODE
STAT
CHARGING
R4
VOUT = 1 +
• 3.0
The CP output can be used for a UVLO indicator. Regard-
less of the state of EN, the CP output reflects the volt-
age of the VCC (adapter) input. When VCC is above UVLO,
CP is high, 2.8V. When VCC is below UVLO, CP is low, 0V.
The CP pin can also put the device into the charge mode
whenever the adaptor has power, by connecting it to the
BIP pin.
R3
FIGURE 1
Remote Kelvin Sensing at the Battery
Another nice feature of the SC801 is its ability to sense
the battery voltage directly at the battery with its Kelvin
BSEN pin. This allows the designer great flexibility in PCB
layout and achieves a much greater accuracy in sensing
the battery voltage where it counts, at the battery termi-
nals! Therefore, when laying out the PCB the designer
should route the BSEN pin directly to the terminal at which
the battery gets connected. In addition, in the LDO mode,
the BSEN pin will still need to sense the output voltage.
In LDO mode, the BSEN pin becomes the regulation feed-
back for the control-loop. In this case it is sensing the
output voltage of itself, since the battery is not in place.
Therefore BSEN should never be left floating.
The OVP LED will light whenever the SC801 is enabled
and there is an overvoltage on the VCC pins. When this
occurs the SC801 will turn off and stay off as long as the
overvoltage condition remains. As soon as the overvolt-
age is removed the SC801 will resume operation. The
OVP LED will not light if the part is disabled, even though
an overvoltage is present on the VCC pins.
Configuring the Output Voltage to the Battery
The battery voltage is set by the VPRGM pin. If this pin 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. The VPRGM
pin can be tied to the CP pin for 4.2V operation and ground
for 4.1V operation. For a value other than 4.1V or 4.2V a
resistor divider is required. This divider is set between
the VOUT pin and the VPRGM pin with the divider tap
connected to the BSEN pin. The schematic for such a
connection and the equation to set the output voltage is
given in Figure 1. The output voltage for Figure 1 will be
set to 4.77V with the resistors shown. The capacitor C1
may be needed for stability and or reduced ripple volt-
age. It is advisable to leave room on the PCB for adding
this capacitor, since it can be left out if it is not needed.
The evaluation board does have a place for the resistor
divider and capacitor to allow an adjustable voltage to
be set on this board via R1, R2 and C2 (see schematic
on page 10). With JP7 removed, jumper JP2 should be
added to complete the changes required for adjustable
mode operation on the evaluation board. For further
evaluation board information, see the section tilted Evalu-
ation Board.
Capacitor Selection
Input and output capacitors can be low cost ceramic type.
The output capacitance range is 1uF to 4.7uF. The input
capacitor should be between 0.1uF to 1uF.
Overcurrent and Temperature Protection
Overcurrent protection is inherent to the SC801. The
SC801 operates as a current source and the output cur-
rent is limited by the mode it is in at the time. If in the
fast-charge mode the current is limited by the IPRGM
resistor, the fast-charge current. When the output volt-
age is less than 2.8V, the current is limited by the ITERM
resistor, the pre-charge current. Both of these functions
protect the device in an event of a short circuit condition
on the output. In the LDO mode the current is limited to
the fast-charge current, provided there is voltage on the
output. Under a short circuit condition in the LDO mode
the current will enter a hiccup mode. The temperature
shutdown can protect the device in conditions of excess
current as well, by shutting down the device when its die
temperature exceeds 165oC.
2002 Semtech Corp.
7
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