ATA5278_06 ATMEL [ATMEL Corporation], ATA5278_06 Datasheet - Page 17

• Manufacturer Part Number: ATA5278_06
• Description: Stand-alone Antenna Driver
• Manufacturer: ATMEL [ATMEL Corporation]

3.13
Figure 3-13. Antenna Current Regulation Loop
4832C–RKE–02/06
Current Regulation
Selected
current
The antenna driver stage and the boost converter are thermally monitored in order to protect
them from overheating, and the output pin DRV1 is short-circuit protected by means of current
limitation. For further details, please refer to the section
The current sensor system is equipped with a zero-crossing detector and a sample and hold
stage. The zero-crossing detector provides the synchronization signal for the driver control logic,
which then calculates the phase shift between the antenna driver output signal and the current
flowing through the antenna. Based on this phase information, the sample and hold stage is con-
trolled in order to sample the top point of the input signal, hence the peak current value.
A main feature of the ATA5278 is its ability to generate a stabilized magnetic field with a con-
nected LC antenna, mainly independent of the battery voltage and the frequency mismatch
between the driver output frequency and the antenna resonance frequency.
The input signal for the regulation loop in
defined in configuration register 1. An external shunt resistor of 1 , which has to be connected
to the VSHUNT pin, is used to measure the current in the LC antenna. As the peak voltage over
this resistor is directly linked with the peak current in the antenna and hence the magnetic field
strength, this value can be seen as output. This signal is sampled and held by an internal stage
controlled by the control logic. The difference of the input signal and the sampled signal then
controls an integrator. The parameter of this stage can be influenced with an externally applied
charging capacitor connected to the CINT pin. The charging/discharging behavior of the integra-
tor stage is described in
+
-
Integrator
CINT
Figure 3-14 on page
converter
VBAT
Boost
T
Current
sample
VDS
hold
and
Figure 3-13
18.
DMOS half
bridge
is the selected antenna current, which is
“Fault Diagnosis” on page
DRV1
LC-antenna
VSHUN
ATA5278
T
20.
17