BQ50002 Datasheet, PDF (9/35 Pages) Texas Instruments – Low-Cost 5-V Wireless Power Transmitter Analog Front

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bq50002
SLUSBW1A – OCTOBER 2015 – REVISED OCTOBER 2015
7.3 Feature Description
7.3.1 Demodulator
The embedded demodulator outputs at least one valid bit stream under all modulation conditions that can be
used by the accompanied bq500511 controller in order to comply with WPC specification.
More specifically, the WPC worst case condition is defined as the transmitter operating at the minimum
modulation level, and the receiver coil is measured by certain x, y and z axis distance to the center of the
transmitter coil.
Analog demodulation channel function diagram:
• The diagram below from the WPC spec document explains the concept of Minimum Modulation. The peak-to-
peak amplitude difference in TX coil waveform between HI and LO states is 400 mV. With 20-V_pp carrier
waveform, and 400-mV_pp modulation, with a typical divider it translates to 1 V_pp ±20 mV_pp at the input of the
demodulator channel.
• The difference of the amplitude of the primary cell voltage in the HI and LO state is at least 200 mV.
During a transition the primary cell current and primary cell voltages are undefined. See Figure 3.
t_S
LO State
t_S
t_T
HIGH State
Modulation Depth
t_S
t_T
HIGH State
t_S
LO State
100%
Figure 3. Amplitude Modulation of the Power Signal
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