SC805AMLTRT datasheet(9/17 Pages) SEMTECH

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SC805A

POWER MANAGEMENT

Monitor Mode

When a charge cycle is completed, the SC805A output

turns off and the device enters monitor mode. If the

voltage of the battery falls below the recharge threshold

of CV-00mV 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 µA

over temperature. The status of the charger output as a

function of RTIME, and VOUT current is shown below.

Output

State

Rtime

Timer

VOUT current

VCC

N/A

T < Timer

N/A

OFF

T > Timer

N/A

Low

Disabled

> termination

OFF

Low

Disabled

< termination

Charge Timer

The timer on the SC805A is used as protection in the case

of a faulty battery and to maximize charging capacity. Con-

nect a resistor from the RTIME pin to GND to select the

desired charge time duration according to the following

equation.

2.5HRS

39.2k

TIME

CHARGE

TIME

The timer is programmable over the range of to 0 hours.

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 SC805A. One implementation of

this feature is discussed in the NOBAT operating section.

The SC805A will automatically turn off the output when

the charge timer times out.

NOBAT Output

The SC805A detects the absence of the battery by monitor-

ing 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 configuration 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 SC805A 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 SC805A.

LDO Mode

The SC805A 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 SC805A 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 voltage with a current limit

set by the resistor tied to the IPRGM pin.

EN-NTC Interface

The enable pin on the SC805A provides three functions:

device disable, battery detection, and NTC temperature

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

the pin to GND. It can also be connected to an external

resistor divider consisting of a resistor and an NTC Thermis-

tor to disable the charge cycle when the temperature is out

of range. If the pin is pulled to VCC the SC805A will signal

a ‘No Battery’ condition on the NOBAT pin.

Note: the SC805A 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.

The NTC external component configuration is shown in the

typical application schematic on Page of the datasheet.

When the NTC voltage from the divider is above or below the

cold and hot temperature threshold values, the SC805A

will suspend the charge cycle by turning off the output,

freezing the charge timer, and indicating a fault on the

CHRGB LED. Hysteresis is included for both hot and cold

thresholds to avoid chatter at the NTC trip points. When

the temperature returns to the valid range, the SC805A will

automatically resume the charge cycle. The charge timer

will time-out when the SC805A output on-time exceeds the

timer setting regardless of how long it has been disabled

Applications Information (Cont.)

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