SC802 datasheet(10/16 Pages) SEMTECH

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SC802/SC802A

POWER MANAGEMENT

Prelimi-

nary

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:

3.0

VOUT

⎟

⎠

⎞

⎜

⎝

⎛ +

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.

kHz

100

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.

RT1

THERMISTOR

1uF

CHARGER VIN

ADC Iset

Adjust Mode Schematic

2.2uF

SC802

VCC

BSEN

IPRGM

EN/NTC

ITERM

VOUT

RTIM

CHRGB

VPRGM

CPB

RFGND

BIPB

VCC

GND

VOUT

AFC

CHARGER

BATTERY

PRESENT

CHARGE

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.....

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