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AT77C102B Datasheet(PDF) 15 Page - ATMEL Corporation

Part No. AT77C102B
Description  Thermal Fingerprint Sensor with 0.4 mm x 14 mm (0.02 x 0.55) Sensing Area and Digital Output (On-chip ADC)
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Maker  ATMEL [ATMEL Corporation]
Homepage  http://www.atmel.com
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AT77C102B Datasheet(HTML) 15 Page - ATMEL Corporation

 
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15
5364A–BIOM–09/05
AT77C102B
Figure 3-11. Nap Mode
In nap mode, all internal transistors are in shut mode. Only leakage current is drained in the
power supply, generally less than the tested value.
3.15
Static Current Consumption
When the clock is stopped (set to 1) and the reset is low (set to 0), the device’s analog sections
drain some current, whereas, if the outputs are connected to a standard CMOS input, the digital
section does not consume any current (no current is drained in the I/O). In this case the typical
current value is 5 mA. This current does not depend on the voltage (it is almost the same from 3
to 3.6V).
3.16
Dynamic Current Consumption
When the clock is running, the digital sections, and particularly the outputs if they are heavily
loaded, consume current. In any case, the current should be less than the testing machine (120
pF load on each I/O), and a maximum of 50 pF is recommended.
The AT77C102B, running at about 1 MHz, consumes less than 7 mA on the V
CC pin.
3.17
Temperature Stabilization Power Consumption (TPP Pin)
When the TPE pin is set to 1, current is drained via the TPP pin. The current is limited by the
internal equivalent resistance given in Table 3-4 on page 6 and a possible external resistor.
Most of the time, TPE is set to 0 and no current is drained in TPP. When the image contrast
becomes low because of a low temperature differential (less than 1 Kelvin), then it is recom-
mended to set TPE to 1 for a short time so that the dissipated power in the chip elevates the
temperature, allowing contrast recovery. The necessary time to increase the chip’s temperature
by one Kelvin depends on the dissipated power, the thermal capacity of the silicon sensor and
the thermal resistance between the sensor and its surroundings. As a rule of thumb, dissipating
300 mW in the chip elevates the temperature by 1 Kelvin in one second. With the 30
Ω typical
value, 300 mW is 3V applied on TPP. If the power supply is 3.6V, an external resistor must be
added in the application to limit the current under 100 mA.
Nap
Clock PCLK
Reset RST
Nap mode


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