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 2004 Semtech Corp.

www.semtech.com

SC801

POWER MANAGEMENT

Applications Information (Cont.)

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.

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.

SC801

14

1

3

7

4

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9

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2

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16

12

VCC

BSEN

IPRGM

EN

ITERM

VOUT

OVP

STAT

VPRGM

CP

NC

BIP

VCC

GND

VOUT

NC

PRESENT

+5V

BATTERY

C2

1uF

C1

330pF

FAULT

R4

59K

R3

100K

CHARGER

STATUS

C3

2.2uF

R1

R2

3.0

R3

R4

1

VOUT

•











 +

=

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.....

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

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