5.11.1 ASK communication
A state (either HI or LO) is characterized by the amplitude being constant (with a certain variation Δ) for at least
150 ms.
If the power receiver and power transmitter coils are properly aligned, then for all appropriate loads, at least one
of the following three conditions shall apply.
• The difference of the amplitude of the transmitter coil current in the high and low state is at least 15 mA.
• The difference of the amplitude of the transmitter coil voltage in the high and low state is at least 200 mV.
• The difference of the transmitter coil current in the high and low state is at least 15 mA. The transmitter coil
current is measured at instants in time that correspond to one quarter of the cycle of the control signal
driving the half-bridge inverter.
Figure 36. HI and LO states in ASK communication
Table 3. HI and LO state parameters
Parameter
Symbol Value Unit
Maximum transition time
t
T
100 µs
Minimum stable time
t
S
150 µs
Current amplitude variation Δ 8 mA
Voltage amplitude variation Δ 110 mV
The power receiver uses a differential bi-phase encoding scheme to modulate the data bits onto the power signal.
The power signal is then demodulated by the power transmitter demodulation circuit and the demodulated signal
is processed.
The communication itself is carried out via packets. Each packet consists of 4 parts and each of those parts
consists of several bits/bytes.
Each communication bit is synchronized to the power receiver’s internal 2 kHz clock signal period. A ONE bit is
encoded as two transitions of the power signal, while a ZERO bit is encoded as a single transition.
UM3154
Bidirectional communication
UM3154 - Rev 2
page 30/81
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