SLOU186F
–
AUGUST 2006
–
REVISED AUGUST 2010
5
System Description
5.1
Power Supplies
The positive supply pin, VIN (pin 2) has an input voltage range of 2.7 V to 5.5 V. The positive supply input
sources three internal regulators with output voltages V
DD_RF
, V
DD_A
and V
DD_X
that use external bypass
capacitors for supply noise filtering. These regulators provide enhanced PSRR for the RFID reader
system.
The regulators are not independent and have common control bits for output voltage setting. The
regulators can be configured to operate in either automatic or manual mode. The automatic regulator
mode setting ensures an optimal compromise between regulator PSRR and highest possible supply
voltage for RF output power. Whereas, the manual mode allows the user to manually configure the
regulator settings.
V
DD_RF
The regulator V
DD_RF
(pin 3) is used to source the RF output stage. The voltage regulator can
be set for either 5-V or 3-V operation. When configured for the 5-V operation, the output
voltage can be set from 4.3 V to 5 V in 100-mV steps. The current sourcing capability for 5-V
operation is 150 mA maximum over the adjusted output voltage range.
When configured for 3-V operation, the output can be set from 2.7 V to 3.4 V, also in 100-mV
steps. The current sourcing capability for 3-V operation is 100 mA maximum over the adjusted
output voltage range.
V
DD_A
Regulator V
DD_A
(pin 1) supplies voltage to analog circuits within the reader chip. The voltage
setting is divided in two ranges. When configured for 5-V operation, the output voltage is fixed
at 3.5 V.
When configured for 3-V operation, the output can be set from 2.7 V to 3.4 V in 100-mV steps.
Note that when configured, both V
DD_A
and V
DD_X
regulators are configured together
(their settings are not independent).
V
DD_X
Regulator V
DD_X
(pin 32) can be used to source the digital I/O of the reader chip together with
other external system components. When configured for 5-V operation, the output voltage is
fixed at 3.4 V.
When configured for 3-V operation, the output voltage can be set from 2.7 to 3.4 V in 100-mV
steps. The total current sourcing capability of the V
DD_X
regulator is 20 mA maximum over the
adjusted output range. Note that when configured, both V
DD_A
and V
DD_X
regulators are
configured together (their settings are not independent).
V
DD_PA
The V
DD_PA
pin (pin 4) is the positive supply pin for the RF output stage and is externally
connected to the regulator output V
DD_RF
(pin 3).
5.1.1
Negative Supply Connections
The negative supply connections are all externally connected together (to GND). The substrate connection
is V
SS
(pin 10), the analog negative supply is V
SS_A
(pin 15), the logic negative supply is V
SS_D
(pin 29),
the RF output stage negative supply is V
SS_TX
(pin 6), and the negative supply for the RF receiver input is
V
SS_RX
(pin 7).
5.1.2
Digital I/O Interface
To allow compatible I/O signal levels, the TRF7960/61 has a separate supply input V
DD_I/O
(pin 16), with
an input voltage range of 1.8 V to 5.5 V. This pin is used to supply the I/O interface pins (I/O_0 to I/O_7),
IRQ, SYS_CLK, and DATA_CLK pins of the reader. In typical applications, V
DD_I/O
is connected directly to
V
DD_X
to ensure that the I/O signal levels of the MCU are the same as the internal logic levels of the
reader.
Copyright
©
2006
–
2010, Texas Instruments Incorporated
System Description
11
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