AT77C104BCH08YV Atmel, AT77C104BCH08YV Datasheet - Page 33

• Manufacturer Part Number: AT77C104BCH08YV
• Manufacturer: Atmel

Specifications of AT77C104BCH08YV

• Lead Free Status / Rohs Status: Compliant

15. Temperature Stabilization Function and Watchdog
5347F–BIOM–3/08
The sensor has an embedded temperature stabilization unit that identifies a difference in tem-
perature between the finger and the sensor. When this difference is increased, the images are
more contrasted. This function is optional and its use depends on the quality of the image pro-
cessing software, therefore its management should be decided together with the image
processing software.
In order to limit excessive current consumption by the use of the temperature stabilization func-
tion, a watchdog has been implanted in the sensor. The local oscillator stops the heating of the
module after a defined time. The oscillator should not be stopped as long as watchdog is active,
otherwise the clock stops automatically.
When heating of the sensor is requested '1' is written in bit 6 of the HEATCTRL
register) and the watchdog is enabled '1' is written in bit 5 of the HEATCTRL register), the sen-
sor is heated during ‘n’ seconds.
Due to the oscillator frequency dispersion, the value of n is:
2 seconds (minimum) < n = 4 seconds (typical) < 7 seconds (maximum).
The accuracy of n is not important since the heat register can be enabled successively.
The level of power consumption is programmable. Two pre-programmed values are set to 50 or
100 mW.
The dissipated die power is quasi constant over a significant supply voltage range as shown
below (mode 50 mW selected):
Note:
This function is useless for navigation and click modes.
5,40E-02
5,30E-02
5,20E-02
5,10E-02
5,00E-02
4,90E-02
4,80E-02
2
2,2
2,4
2,6
Power = f ( Vdd )
2,8
Power = f ( Vdd)
VDD
3
3,2
3,4
AT77C104B
3,6
3,8
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