ZSC31015EIG1-R datasheet(14/52 Pages) IDT

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November 14, 2016

ZSC31015 Datasheet

2.2.

Analog Front End

2.2.1.

Bandgap/PTAT and PTAT Amplifier

The highly linear Bandgap/PTAT section provides the PTAT signal to the ADC, which allows accurate tempera-

ture conversion. In addition, the ultra-low ppm Bandgap provides a stable voltage reference over temperature for

the operation of the rest of the IC. If the bridge is not near the ZSC31015, an external diode can be used for

temperature measurement/compensation.

The temperature signal (internal PTAT or external diode) is amplified through a path in the Pre-Amp and fed to

the ADC for conversion. The most significant 12-bits of this converted result are used for temperature

measurement and temperature correction of bridge readings. When temperature is output in Digital Mode, only

the most significant 8 bits are given.

When external temperature is selected, add a diode from the ExtTemp pin to ground. The diode is biased with

approximately 50µA during temperature measurement cycles. The voltage level on ExtTemp is amplified through

the Pre-Amp and converted by the ADC. Ensure that the ExtTemp signal is in the range of 150mV to 800mV to

prevent saturation of the ADC. If the selected diode has a sensitivity in the range of 1.9mV/

oC to 3.25mV/oC, a

corrected temperature output (in Digital Mode) can be achieved for a 200

oC temperature span (-50oC to 150oC).

2.2.2.

Bridge Supply

The voltage-driven bridge is usually connected to VDD and ground. As a power savings feature, the ZSC31015

also includes a switched transistor to interrupt the bridge current via pin 1 (Bsink). The transistor switching is

synchronized to the analog-to-digital conversion and released after finishing the conversion. To utilize this feature,

the low supply of the bridge should be connected to Bsink instead of ground.

Depending on the programmable update rate, the average current consumption (including bridge current) can be

reduced to approximately 20%, 5%, or 1%. Note: this feature has no power savings benefit if using the fastest

update rate mode.

2.2.3.

PREAMP Block

The differential signal from the bridge is amplified through a chopper-stabilized instrumentation amplifier with very

high input impedance designed for low noise and low drift. This pre-amp provides gain for the differential signal

and re-centers its DC to VDD/2. The output of the Pre-Amp block is fed into the ADC. The calibration sequence

performed by the digital core includes an auto-zero sequence to null any drift in the Pre-Amp state over

temperature.

The Pre-Amp can be set to a gain of 6, 24, 48, or 96 through an EEPROM setting.

The inputs to the Pre-Amp from (VBN/VBP pins) can be reversed via an EEPROM configuration bit.

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