LTC2990I(RevD) データシートの表示（PDF） - Linear Technology

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LTC2990I
(Rev.:RevD)

Quad I2C Voltage, Current and Temperature Monitor

Linear Technology 

LTC2990

Applications Information

Device Configuration

The LTC2990 is configured by writing the control register

through the serial interface. Refer to Table 5 for control

register bit definition. The device is capable of many ap-

plication configurations including voltage, temperature and

current measurements. It is possible to configure the device

for single or repeated acquisitions. The device can make

single measurements, or in continuous mode, repeated

acquisitions. When the device is configured for multiple

measurements, the order of the measurements is fixed.

For repeated acquisitions, only an initial trigger is required

after which data registers are continuously refreshed with

new data. As each new data result is ready, the MSB of the

corresponding data register is set, and the corresponding

status register bit is set. These bits are cleared when the

corresponding data register is addressed. The configura-

tion register value at power-up causes the part to measure

only the internal temperature sensor when triggered. The

four input pins V1 through V4 will be in a high impedance

state, until configured otherwise, and a measurement is

triggered. The data registers are double-buffered in order

to ensure upper and lower data bytes do not become out

of sync. Read operations must be terminated in order to

avoid an indefinitely paused wait state. Reading the STATUS

register does not interrupt measurement data updates.

In a polling system, it is recommended that the STATUS

register be tested for new data, this prevents unnecessary

delays updating the measurement registers.

Data Format

The data registers are broken into 8-bit upper and lower

bytes. Voltage and current conversions are 14-bits. The

upper bits in the MSB registers provide status on the

resulting conversions. These status bits are different for

temperature and voltage conversions:

Temperature: Temperature conversions are reported as

Celsius or Kelvin results described in Tables 8 and 9,

each with 0.0625 degree-weighted LSBs. The format is

controlled by the control register, Bit 7. All temperature

formats, TINT , TR1 and TR2 are controlled by this bit. The

Temperature MSB result register most significant bit

(Bit 7) is the DATA_VALID bit, which indicates whether

the current register contents have been accessed since

the result was written to the register. This bit will be set

when new data is written to the register, and cleared when

accessed. Bit 6 of the register is a sensor-shorted alarm.

This bit of the corresponding register will be high if the

remote sensor diode differential voltage is below 0.14V.

The LTC2990 internal bias circuitry maintains this voltage

above this level during normal operating conditions. Bit 5

of the register is a sensor open alarm. This bit of the cor-

responding register will be high if the remote sensor diode

differential voltage is above 1.0VDC. The LTC2990 internal

bias circuitry maintains this voltage below this level during

normal operating conditions. The two sensor alarms are

only valid after a completed conversion indicated by the

data_valid bit being high. Bit 4 through Bit 0 of the MSB

register are the conversion result bits D[12:8], in two’s

compliment format. Note in Kelvin results, the result will

always be positive. The LSB register contains temperature

result bits D[7:0]. To convert the register contents to

temperature, use the following equation:

T = D[12:0]/16.

See Table 10 for conversion value examples.

Voltage/Current: Voltage results are reported in two respec-

tive registers, an MSB and LSB register. The Voltage MSB

result register most significant bit (Bit 7) is the data_valid

bit, which indicates whether the current register contents

have been accessed since the result was written to the

register. This bit will be set when the register contents are

new, and cleared when accessed. Bit 6 of the MSB register

is the sign bit, Bits 5 though 0 represent bits D[13:8] of

the two’s complement conversion result. The LSB register

holds conversion bits D[7:0]. The LSB value is different

for single-ended voltage measurements V1 through V4,

and differential (current measurements) V1 – V2 and V3

– V4. Single-ended voltages are limited to positive values

in the range 0V to 3.5V. Differential voltages can have input

values in the range of –0.300V to 0.300V.

Use the following equations to convert the register values

(see Table 10 for examples):

VSINGLE-ENDED = D[14:0] • 305.18µV, if Sign = 0

VSINGLE-ENDED = (D[14:0] +1) • –305.18µV, if Sign = 1

VDIFFERENTIAL = D[14:0] • 19.42µV, if Sign = 0

VDIFFERENTIAL = (D[14:0] +1) • –19.42µV, if Sign = 1

Current = D[13:0] • 19.42µV/RSENSE, if Sign = 0

2990fd

For more information www.linear.com/LTC2990

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