SL900A datasheet(53/90 Pages) AMSCO

53 / 90 page

ams Datasheet: 2014-May-06 [v1-01]

SL900A – 53

Ex t e rnal Sensor Fr ont - End (SFE)

The SL900A device can process the internal temperature sensor,

the battery voltage and up to 2 external sensors. The result of

the A/D conversion can be logged to the EEPROM or sent

directly back to the interrogator (if the GET SENSOR VALUE

command is used). The external sensors and the integrated

temperature sensor can only be processed in serial manner. This

is done through a multiplex amplifier, as the SL900A device has

only one A/D converter integrated.

Figure 43:

External Sensor Front End

SFE Interface

The external sensor interface consists of 4 pads:

• EXT1 – connection for external sensor 1 that can be a

linear-resistive sensor, a DC voltage source (sensor with

external analog processing), capacitive and resistive

sensors with AC driving,

• EXT2 – connection for external sensor 2 that can be a

linear-conductive sensor, a reverse-polarized diode, DC

voltage source with serial resistance or a DC current

source to VSS,

• EXC – supply voltage for the external sensors or a AC signal

source for external sensors that do not allow a DC voltage.

•VREF – reference voltage (Vo2) pin used for capacitive and

resistive sensors with AC excitation.

External Sensor Front-End (SFE)

EXC

EXT1

VREF

V-AGC

I-AGC

Programmable Current

Sources

EXT2

SFE CONTROLS

IRQ

MEMORY

TIMING,

REFERENCE

Pre-

drive

current

REFERENCES

ARC

ext_sw

Vbat

S/H

shelf_life

Vbat

IRQ

SL900A Datasheet(PDF) 53 Page - ams AG

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