PIC12F635ESLASHST datasheet(94/196 Pages) MICROCHIP

94 / 196 page

PIC12F635/PIC16F636/639

DS41232B-page 92

Preliminary

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

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.

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

DFLAT2

VDD

RCOM

DLIM

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.

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