SC908EVB datasheet(21/30 Pages) SEMTECH

21 / 30 page

SC908

Applications Information (continued)

from 2.77V to 2.98V, ±10%. The low battery fault threshold

is set by the relationship

DET

= 3.9 μA × R

RLBAT

× 2.42

RLBAT

must satisfy the condition

294kΩ ≤ R

RLBAT

≤ 316kΩ

Connect RLBAT to GND to disable the Low Battery Detector

fault. The Low Battery Detector warning remains active.

Status Outputs

Four charger status outputs/LED drivers are provided.

CPB (Charger Present)

CHRGB (Charge Active)

FLTB (Fault)

LBATB (Low Battery Warning)

These outputs are active-low, open drain NMOS drivers

capable of sinking up to 2mA each. The state of each, in

various operating conditions, is defined in Tables 2, 3,

and 4.

When the VAD voltage is below its UVLO threshold (no

charging adapter is present), the CPB and CHRGB outputs

are off (high impedance). The FLTB and LBATB outputs

indicate the battery voltage as defined in Table 2.

•

When V

VAD

is between its UVLO and OVP thresholds, V

VAD

is valid to charge, and the CPB output is low indicating

that a charging adapter is present.

The CHRGB output indicates the battery charging status.

The charger-present status output states are described in

Table 3. When pre-charging or when the output current

is greater than I

TERM

, CHRGB is low. The CHRGB output is

latched off (high) when the output current becomes less

than I

TERM

during the charge cycle (and the battery voltage

is above the recharge threshold, V

BSEN

> V

- VT

ReQ

). This

latch is reset when the battery enters a recharge cycle

BSEN

< V

- VT

ReQ

), or for any NTC_EN range other than

OK-to-charge, or if V

VAD

is above or below the VAD valid-

to-charge range, allowing CHRGB to become active again

when charging resumes.

When a charging adapter is present, the FLTB and LBATB

outputs are redefined to reflect the interaction of the

battery voltage, charging state, and charging faults, as

described in Table 3. The FLTB output is activated when

the device experiences a charger fault condition, or

(together with LBATB output) when the battery voltage is

less than the resistor-programmed low-battery detector

threshold, V

DET

. This output can be used to notify the

system controller of a fault condition when connected to

an interrupt input, or it can be used like CPB and CHRGB

to drive an indicator LED.

Table 2 — Status Output State, Charging Adapter Absent

Status Pins Output State

(on = low)

Conditions

Description

and

Comments

Adapter Voltage

(mutually exclusive)

Battery Voltage

(mutually exclusive)

on = open drain output driver is active

off = output is not active

T = listed condition is true

F = listed condition is false

- = don’t care

Blank = mutually exclusive with another condition

off

No Charging Adapter, Battery Voltage Good

off

No Charging Adapter, Low Battery Voltage Warning

off

No Charging Adapter, Low Battery Shutdown Request

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