Datasheet

PIC12F635/PIC16F636/639
DS41232D-page 110 © 2007 Microchip Technology Inc.
11.26 Factory Calibration
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.
11.27 De-Q’ing of Antenna Circuit
When the transponder is close to the base station, the
transponder coil may develop coil voltage higher than
V
DE_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.
11.28 Battery Back-up and Batteryless
Operation
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.
Figure 11-8 shows an example of the external circuit for
the battery back-up.
FIGURE 11-8: LF FIELD POWERING AND BATTERY BACK-UP EXAMPLE
Note: Voltage on LCCOM combined with coil input
voltage must not exceed the maximum LC
input voltage.
LCX
LCY
LCZ
VBAT
DBLOCK
CPOOL
DFLAT1
RLIM
LCCOM
CCOM
Air Coil
D
FLAT2
CZ
CY
CX
VDD
RCOM
DLIM
LX
LY
LZ
Legend: CCOM = LCCOM charging capacitor.
C
POOL = Pool capacitor (or battery back-up capacitor), charges in field and powers device.
D
BLOCK = Battery protection from reverse charge.
Schottky for low forward bias drop.
DFLAT = Field rectifier diodes.
D
LIM = Voltage limiting diode, may be required to limit VDD voltage when in strong fields.
R
COM =CCOM discharge path.
R
LIM = Current limiting resistor, required for air coil in strong fields.