SC805 datasheet(7/15 Pages) SEMTECH

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 2005 Semtech Corp.

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SC805

POWER MANAGEMENT

of CV-100mV 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

1µA over temperature. The status of the charger output

as a function of RTime, and IOUT is shown below.

Charge Timer

The timer on the SC805 is used as protection in the case

of a faulty battery and to maximize charging capacity.

Connect a resistor from the RTIME pin to GND to select

the desired charge time duration according to the follow-

ing equation.

The timer is programmable over the range of 1 to 10

hrs. To disable the charge timer connect RTIME to GND.

Driving the RTIME pin to VCC will disable the timer and

select LDO-mode operation for the SC805. One imple-

mentation of this feature is discussed in the NOBAT op-

erating section.

The SC805 will automatically turn off the output when

the charge timer times out.

2.5hrs

39.2k

Time

Charge

TIME

•













NOBAT output

The SC805 detects the absence of the battery by moni-

toring the voltage on the NTC pin. When the NTC pin

voltage exceeds 95% of VCC the NOBAT output is driven

high. This function utilizes the standard NTC configura-

tion with the NTC component residing in the battery pack.

When the battery is removed the NTC element in the

resistor divider is missing and the NTC voltage is pulled

up to VCC.

The NOBAT output can be used to signal the system that

the battery has been removed, drive an external LED, or

fed back to the SC805 to select LDO-mode.

Connect the NOBAT pin to the RTIME pin to select LDO

mode when the battery is removed and re-enable the

output of the SC805.

LDO Mode

The SC805 is designed to work with or without a battery.

If the battery is not in place the device can enter LDO

mode. In this mode the SC805 will act like a low dropout

regulator. The input pin RTIME is used to select LDO

mode. If RTIME is high the device will be in LDO mode.

When LDO-mode is selected and the EN-NTC pin is greater

than 90% of VCC the output will be on in LDO mode.

During LDO mode the device will regulate the output volt-

age with a current limit set by the resistor tied to the

IPRGM pin.

EN-NTC Interface

The Enable pin on the SC805 provides three functions;

device disable, battery detection, and NTC temperature

protection. It can be used to turn off the device by driv-

ing the pin to Ground. It can also be connected to an

external resistor divider consisting of a resistor and an

NTC Thermistor to disable the charge cycle when the tem-

perature is out of range. If the pin is pulled to VCC the

SC805 will signal a ‘No Battery’ condition on the NOBAT

pin. Note that the SC805 will be disabled due to the

NTC function when the ‘No Battery’ condition is detected

due to the NTC feature. The NTC temperature fault can

be overridden to re-enable the output of the charger for

no battery conditions as described in the NOBAT section

of the datasheet.

Applications Information (Cont.)

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