LTC2990CMSTRPBF datasheet(11/24 Pages) LINER

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LTC2990

2990f

applicaTions inForMaTion

Device Configuration

The LTC2990 is configured by writing the control register

through the serial interface. Refer to Table 4 for control

plication configurations including voltage, temperature

and current measurements. It is possible to configure the

device for single or repeated acquisitions. For repeated

acquisitions,onlytheinitialtriggerisrequiredandnewdata

is written over the old data. Acquisitions are frozen during

serial read data transfers to prevent the upper and lower

data bytes for a particular measurement from becoming

out of sync. Internally, both the upper and lower bytes

are written at the same instant. Since serial data transfer

timeout is not implemented, failure to terminate a read

operation will yield an indefinitely frozen wait state. The

device can also make single measurements, or with one

trigger,allofthemeasurementsfortheconfiguration.When

the device is configured for multiple measurements, the

order of measurements is fixed. 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 configuration register value at power-up

yields the measurement of only the internal temperature

sensor, if triggered. The four input pins V1 through V4 will

be in a high impedance state, until configured otherwise,

and a measurement triggered.

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 7 and 8,

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

remotesensordiodedifferentialvoltageisbelow0.14VDC.

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

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 9 for conversion value examples.

Voltage/Current:Voltageresultsarereportedintworespec-

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

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 9 for examples):

VSINGLE-ENDED = D[13:0] • 305.18µV

VDIFFERENTIAL = D[13:0] • 19.42µV, if Sign = 0

VDIFFERENTIAL = (D[13:0] +1) • –19.42µV, if Sign = 1

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

Current=(D[13:0]+1)•–19.42µV/RSENSE,ifSign=1,

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