DS2761AX datasheet(6/24 Pages) DALLAS

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DS2761

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POWER MODES

The DS2761 has two power modes: active and sleep. While in active mode, the DS2761 continually

measures current, voltage, and temperature to provide data to the host system and to support current

accumulation and Li+ safety monitoring. In sleep mode, the DS2761 ceases these activities. The DS2761

enters sleep mode when any of the following conditions occurs:

§ The PMOD bit in the Status Register has been set to 1 and the DQ line is low for longer than

2s (pack disconnection)

§ The voltage on VIN drops below undervoltage threshold VUV for tUVD (cell depletion)

§ The pack is disabled through the issuance of a SWAP command (SWEN bit = 1)

The DS2761 returns to active mode when any of the following occurs:

§ The PMOD bit has been set to 1 and the SWEN bit is set to 0 and the DQ line is pulled high

(pack connection)

§ The PS pin is pulled low (power switch)

§ The voltage on PLS becomes greater than the voltage on VIN (charger connection) with the SWEN bit

set to 0

§ The pack is enabled through the issuance of a SWAP command (SWEN bit = 1)

The DS2761 defaults to sleep mode when power is first applied.

Li+ PROTECTION CIRCUITRY

During active mode, the DS2761 constantly monitors cell voltage and current to protect the battery from

overcharge (overvoltage), overdischarge (undervoltage), and excessive charge and discharge currents

(overcurrent, short circuit). Conditions and DS2761 responses are described in the sections below and

summarized in Table 2 and Figure 3.

Table 2. Li+ PROTECTION CONDITIONS AND DS2761 RESPONSES

ACTIVATION

CONDITION

NAME

THRESHOLD DELAY

RESPONSE

RELEASE

THRESHOLD

Overvoltage

VIN > VOV

tOVD

CC high

VIN < VCE, or

VIS ≤ -2mV

Undervoltage

VIN < VUV

tUVD

CC , DC high,

Sleep Mode

VPLS > VDD

(1)

(charger connected)

Overcurrent, Charge

VIS > VOC

(2)

tOCD

CC , DC high

VPLS < VDD - VTP

(3)

Overcurrent, Discharge

VIS < -VOC

(2)

tOCD

DC high

VPLS > VDD - VTP

(4)

Short Circuit

VSNS > VSC

tSCD

DC high

VPLS > VDD - VTP

(4)

VIS = VIS1 - VIS2. Logic high = VPLS for CC and VDD for DC . All voltages are with respect to VSS. ISNS references current

delivered from pin SNS.

1) If VDD < 2.2V, release is delayed until the recovery charge current (IRC) passed from PLS to VDD charges the battery and

allows VDD to exceed 2.2V.

2) For the internal sense resistor configuration, the overcurrent thresholds are expressed in terms of current: ISNS > IOC for

charge direction and ISNS < -IOC for discharge direction

3) With test current ITST flowing from PLS to VSS (pulldown on PLS)

4) With test current ITST flowing from VDD to PLS (pullup on PLS)

Overvoltage. If the cell voltage on VIN exceeds the overvoltage threshold, VOV, for a period longer than

overvoltage delay, tOVD, the DS2761 shuts off the external charge FET and sets the OV flag in the

protection register. When the cell voltage falls below charge enable threshold VCE, the DS2761 turns the

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