PIC12F635/PIC16F636/639
11.26 Factory Calibration
11.28 Battery Back-up and Batteryless
Operation
Microchip calibrates the AFE to reduce the
device-to-device variation in standby current, internal
timing and sensitivity, as well as channel-to-channel
sensitivity variation.
The device supports both battery back-up and
batteryless operation by the addition of external
components, allowing the device to be partially or
completely powered from the field.
11.27 De-Q’ing of Antenna Circuit
Figure 11-8 shows an example of the external circuit for
the battery back-up.
When the transponder is close to the base station, the
transponder coil may develop coil voltage higher than
VDE_Q. This condition is called “near field”. The AFE
detects the strong near field signal through the AGC
control, and de-Q’ing the antenna circuit to reduce the
input signal amplitude.
Note:
Voltage on LCCOM combined with coil input
voltage must not exceed the maximum LC
input voltage.
FIGURE 11-8:
LF FIELD POWERING AND BATTERY BACK-UP EXAMPLE
VBAT
VDD
LCX
LCY
LCZ
RLIM
DFLAT1
DBLOCK
CPOOL
LX
DLIM
CX
LY
Air Coil
CY
LZ
CZ
LCCOM
DFLAT2
CCOM
RCOM
Legend: CCOM = LCCOM charging capacitor.
CPOOL = Pool capacitor (or battery back-up capacitor), charges in field and powers device.
DBLOCK = Battery protection from reverse charge.
Schottky for low forward bias drop.
DFLAT = Field rectifier diodes.
DLIM = Voltage limiting diode, may be required to limit VDD voltage when in strong fields.
RCOM = CCOM discharge path.
RLIM = Current limiting resistor, required for air coil in strong fields.
DS41232D-page 110
© 2007 Microchip Technology Inc.
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