17
August ’01 Chapter 2. Electrical Description
2.2 Power Supply
2.2.1 VBAT Supply
Most parts of the 3D-AFE are supplied via VBAT input. Typically a 3 V Lithium Battery is
used but also the use of rechargeable batteries is possible. Directly at the TMS37122 input a
Buffer Capacitor (Cbat) should be provided with short connections to VBAT and GND pin.
Eventually also at the Microcomputer and UHF Transmitter input additional capacitor are re-
quired in order to meet the specified maximum power supply ripple (Vripple).
2.2.1.1 Standard Battery Supply
If Standard Battery Supply is desired, the VCCO output of the 3D-AFE is not used. Battery
Backup function (transmission via LF Channel in case of too low battery voltage) is not us-
able. The Charge Capacitor CL can therefore have the recommended standard value. Greater
capacitor values do not influence negatively the Write Distance Expander function. Beside
this it is possible to provide an additional LF Channel in order to overcome interference prob-
lems in this frequency band. The LF Response must take place before the UHF transmission
and is only possible if the battery voltage is above the minimum specified value, because the
supply of Microcomputer and 3D-AFE is not backed up.
Figure 5: Standard Battery Supply - Schematic
2.2.1.2 Rechargeable Battery Supply
If you are using a rechargeable battery, the restrictions described in section 2.2.1.1 can be
overcome. The de-coupling diode at the battery is eliminated (see Figure 6).
Weak batteries can be refreshed in the application or in special charge stations. The Identifi-
cation Device must therefore be placed in a strong continuous RF field so that the Charge Ca-
pacitor voltage (VCL) is in limitation. In this case the Voltage Regulator supplies high
enough voltage and current to the battery via output VCCO (short circuit between VCCO and
VBAT).
VOLT.
REG.
VBAT
3DSUP01.CH4
CR
LR
GND
VCL
RF
µC
Cbat = 22nF
Battery
VCCO
Rectifier
Diode
CL >= 22nF
VBAT
VCL
RF
To Next Page
Loading...
Need help?
General
