mc33690dw Freescale Semiconductor, Inc, mc33690dw Datasheet - Page 6

• Manufacturer Part Number: mc33690dw
• Description: Standalone Tag Reader Circuit Starc
• Manufacturer: Freescale Semiconductor, Inc

© Motorola, Inc., 2002.
Read function
transponder generates an absorption modulation
of the magnetic field. It results in an amplitude/
phase modulation of the current across the
antenna. This information is picked up at the
antenna tap point between the coil and the
capacitor. An external resistive ladder down
scales this voltage to a level compatible with the
demodulator input voltage range (see parameter
V
The demodulator (see figure 2) consists of :
The sampling time is automatically set to take
into account a phase shift due to the tolerances
of the antenna components (L and C) and of the
oscillator. The allowed phase shift measured at
the input RD ranges from -45° to +45°. Assuming
that the phase reference is the falling edge of the
driving signal TD1, this leads to a sampling time
phase ranging from -78.75° to 90° with discrete
steps of 11.25°. After reset condition, the
sampling time phase is +11.25°.
INRD
When answering to the base station, a
- an input stage (emitter follower),
- a sample & hold circuit,
- a voltage follower,
- a low offset voltage comparator.
page 16).
Figure 3 : Current flow when the buffers are switched off
Freescale Semiconductor, Inc.
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L
C
R
A
R
A
A
1
MC33690
TD1
TD2
6
The antenna phase shift evaluation is only
done :
10 to 12),
This is necessary to obtain the best demodulator
performances.
In order to ensure a fast demodulator settling
time after wake up, reset or a write sequence, the
external capacitor C
working voltage.
This preset occurs 256µs after switching the
antenna drivers on and its duration is 128µs.
After wake up or reset, the preset has the same
duration but begins 518µs after clock settling.
After power on reset, VSUP must meet the
minimum specified value, enabling the nominal
operation of VDD, before the start of the preset.
Otherwise the preset must be done by the user
through a standby/wake-up sequence.
Write function
page
switching on/off the output drivers TD1/2.
Once the drivers have been set in high
impedance, the load current flows alternatively
- after each wake-up command (see pages
- or after reset (see page 7).
Whatever the selected configuration (see
VDD
VDD
9), the write function is achieved by
EXT
is preloaded at its
revision 4.8, 5 February 2002