ata5277-pcq ATMEL Corporation, ata5277-pcq Datasheet - Page 12

• Manufacturer Part Number: ata5277-pcq
• Description: Stand-alone Antenna Driver
• Manufacturer: ATMEL Corporation

Coil Driver
Current Adjustment
12
ATA5277 [Preliminary]
The coil driver is composed of a power MOS stage in half-bridge configuration, which is
supplied by a current regulated boost converter. The driver generates a square-wave
output signal to supply the antenna circuit with the carrier frequency. The antenna coil
current is regulated by the voltage of the switch mode power supply. The current is
therefore sensed by a shunt resistor connected between the VSHUNT and the GND
pins of the IC.
To avoid damages in case of short circuits and high currents, the driver is switched off
by the integrated fault detection unit.
To provide an adjustable coil current, the IC is equipped with a voltage regulator com-
posed of a Switch Mode Power Supply (SMPS), which is used if the supply voltage is
too low to reach the desired antenna coil current. In this case, the driver stage voltage is
brought up to the required level (maximum 40 V). The IC contains the control logic and
the switching transistor for the boost converter. All other components like the choke coil
and the capacitor have to be applied externally.
The antenna coil current can be adjusted in 16 steps by modifying the I_Coil0 to I_Coil3
bits in the control register. According to the selected current, the pulse width of the
antenna coil driver signal is adjusted in order to enlarge the control range for the voltage
regulator. The 16 steps are scaled logarithmically and have the follwing current ratings:
Table 9. Current Settings
Note:
Step
16
10
11
12
13
14
15
1
2
3
4
5
6
7
8
9
(1)
1. Default
Current [mA]
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
maximum
maximum
maximum
maximum
maximum
maximum
maximum
maximum
maximum
maximum
maximum
maximum
maximum
maximum
maximum
maximum
/3.158
/2.927
/2.727
/2.5
/2.353
/2.143
/2
/1.846
/1.714
/1.579
/1.463
/1.367
/1.263
/1.165
/1.081
I_Coil0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
I_Coil1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
I_Coil2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
I_Coil3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
4669B–RKE–10/03
P/P Ratio
1/7
1/7
1/7
1/7
2/6
2/6
2/6
2/6
3/5
3/5
3/5
3/5
4/4
4/4
4/4
4/4