SC804 datasheet(9/21 Pages) SEMTECH

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SC804

PRELIMINARY

POWER MANAGEMENT

This adjustment to the fast charge current is obtained

by replacing the ﬁxed V

IPRGM reference voltage with the

AFC voltage. (Note that AFC voltages above VIPRGM will

produce I

VOUT exceeding that programmed as per the Fast-

Charge Mode (CC) section.) For any applied AFC voltage,

FCI must not drop below 130mA, and FCI must always

remain at least 80mA greater than PCI.

Termination Current

Once the battery voltage reaches V

CV the SC804 will

transition from constant current mode to constant voltage

mode. The current through the battery will decrease while

the voltage remains constant as the battery becomes fully

charged. When the current falls below the programmed

termination current set by the termination resistor

connected to the ITERM pin, the SC804 will disable

CHRGB. If the timer is enabled the output will continue

to ﬂoat-charge in CV mode until the timer expires. If the

timer is disabled, the output will turn off as soon as the

termination current level is reached. The equation to set

the termination current is given by:

ITERM can be programmed to be as high as 300mA or as

low as 50mA, though accuracy is not guaranteed below

100mA. ITERM must be programmed to be less than FCI

for correct operation of the charge cycle.

Monitor Mode

When a charge cycle is complete, the SC804 output turns

off and the device enters monitor mode. If the voltage

of the battery falls below the recharge threshold (VCV

- VReQ), the charger will clear the charge timer and re-

initiate a charge cycle. The maximum current drain of the

battery during monitor mode will be no more than 1

μA

over temperature. The status of the charger output as a

function of the timer and IOUT is tabulated below.

Applications Information

Timer

Iout

Output State

T < Timeout

N/A

T > Timeout

N/A

Off

Disabled

< Itermination

Off

ITERM_Typ

ITERM =

× 100

ITERM

Charge Timer

The timer on the SC804 has two functions: to protect in

the event of a faulty battery and to maximize charging

capacity. The RTIM pin is connected to VCC to select the

internal timer, and to GND to disable the timer.

Connecting a resistor between RTIM and GND will program

the total charge time according to the following equation:

with charge time expressed in hours.

The timer is

programmable over the range of 2 to 6 hours. The internal

timer selection results in a charge time of 3 hours. The

SC804 will automatically turn off the output when the

charge timer times out.

NTC Interface

The NTC pin provides an interface to a battery pack

Negative Temperature Coefﬁcient (NTC) thermistor. The

typical NTC network has a ﬁxed resistor from VCC to the

NTC pin, and the battery pack NTC thermistor connected

from the NTC pin to ground. In this conﬁguration, an

increasing battery temperature produces a decreasing

NTC pin voltage, and a decreasing battery temperature

produces an increasing NTC pin voltage.

This conﬁguration is shown in the typical application

schematic on page 1 of this datasheet. When the NTC

voltage from the divider is greater than the high (cold)

threshold or less than the low (hot) threshold, the SC804

suspends the charge cycle by turning off the output,

halting (but not resetting) the charge timer, and indicating

a fault on the FLTB pin. Hysteresis is included for both

high and low NTC thresholds to avoid chatter at the NTC

trip points. When the NTC pin voltage returns to the valid

range, the SC804 automatically resumes the charge cycle.

The charge timer will time-out when the SC804 output on-

time exceeds the timer setting regardless of how long it

has been disabled due to the NTC temperature.

An input voltage between VT

NTCH×V

VCC and the CTO input

voltage V

CTO (VTNTCC×VVCC if CTO is tied to GND) enables

charging. An input voltage outside this range suspends

charging and drives FLTB pin active (low). The internal

NTC thresholds of VT

NTCH and VTNTCC were designed to

3600

Charge time =

(

)

RTIM

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