LTC2942CDCB Просмотр технического описания (PDF) - Linear Technology

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LTC2942CDCB

Battery Gas Gauge with Temperature, Voltage Measurement

Linear Technology 

LTC2942

APPLICATIONS INFORMATION

Status Register (A)

The status of the charge, voltage and temperature alerts

is reported in the status register shown in Table 2.

Table 2. Status Register A (Read only)

BIT NAME

OPERATION

DEFAULT

A[7] Chip Identification 0: LTC2942

0

1: LTC2941

A[6] Reserved

0

A[5] Accumulated Charge Indicates that the value of the

0

Overflow/Underflow ACR hit either top or bottom.

A[4] Temperature Alert Indicates one of the

0

temperature limits was

exceeded.

A[3] Charge Alert High Indicates that the ACR value

0

exceeded the charge threshold

high limit.

A[2] Charge Alert Low Indicates that the ACR value

0

dropped below the charge

threshold low limit.

A[1] Voltage Alert

Indicates one of the battery

0

voltage limits was exceeded.

A[0] Undervoltage

Lockout Alert

Indicates recovery from

X

undervoltage. If set to 1, a

UVLO has occurred and the

contents of the registers are

uncertain.

All status register bits except A[7] are cleared after being

read by the host, if the conditions which set these bits

have been removed.

As soon as one of the three measured quantities exceeds

the programmed limits, the corresponding bit A[4], A[3],

A[2] or A[1] in the status register is set.

Bit A[5] is set if the LTC2942’s accumulated charge registers

(ACR) overflows or underflows. In these cases, the ACR

stays at FFFFh or 0000h and does not roll over.

The undervoltage lockout (UVLO) bit of the status register

A[0] is set if, during operation, the voltage on SENSE+

pin drops below 2.7V without reaching the POR level.

The analog parts of the coulomb counter are switched off

while the digital register values are retained. After recov-

ery of the supply voltage the coulomb counter resumes

integrating with the stored value in the accumulated

charge registers but it has missed any charge flowing

while SENSE+ < 2.7V.

The hard-coded bit A[7] of the status register enables the

host to distinguish the LTC2942 from the pin compatible

LTC2941, allowing the same software to be used with

both devices.

Control Register (B)

The operation of the LTC2942 is controlled by program-

ming the control register. Table 3 shows the organization

of the 8-bit control register B[7:0].

Table 3. Control Register B

BIT NAME

OPERATION

B[7:6] ADC Mode

[11] Automatic Mode.

Performs voltage and temperature

conversion every second.

[10] Manual Voltage Mode.

Performs single voltage

conversion, then sleeps.

[01] Manual Temperature Mode.

Performs single temperature

conversion, then sleeps.

[00] Sleep.

B[5:3]

B[2:1]

Prescaler M

Sets coulomb counter prescaling

factor M between 1 and 128.

Default is 128.

M = 2(4 • B[5] + 2 • B[4] + B[3])

AL/CC Configure Configures the AL/CC pin.

[10] Alert Mode.

Alert functionality enabled.

Pin becomes logic output.

[01] Charge Complete Mode.

Pin becomes logic input and

accepts “charge complete” signal

(e.g., from a charger) to set

accumulated charge register (C,D)

to FFFFh.

[00] AL/CC pin disabled.

[11] Not allowed.

B[0] Shutdown

Shut down analog section to

reduce ISUPPLY.

Default

[00]

[111]

[10]

[0]

Power Down B[0]

Setting B[0] to 1 shuts down the analog parts of the

LTC2942, reducing the current consumption to less than

1μA. All analog circuits are inoperative while the values

in the registers are retained. Note that any charge flowing

while B[0] is 1 is not measured and the charge information

below 1LSB of the accumulated charge register is lost.

2942f

9

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