1.5
Typical Application Circuits
Figure 1-2. Typical 3V Application with External Microcontroller
IRQ
NSS
MISO
32
31
30
29
28
27
26
25
ATEST ATEST
_IO1 _IO2
1
2
3
4
5
6
7
8
24
23
22
21
20
PB2
PB1
MOSI
SCK
RFIN_LB
RFIN_HB
SPDT_RX
SPDT_ANT
ANT_TUNE
SPDT_TX
PB0
CLK_IN
DGND
DVCC
PC5
Atmel
ATA5830
Microcontroller
19
18
17
RF_OUT
VS_PA
PC4
PC3
TEST
_EN
9
10
11
12
13
14 15
16
VDD
VS = 3V
Figure 1-2 shows a key fob application circuit with an external host microcontroller for 315MHz or 433.92MHz running from a
3V lithium cell. The Atmel® ATA5830 stays in OFFMode until NSS(PB5) and NPWRON1(PC1) are used to wake it. In
OFFMode the Atmel ATA5830 draws typically less than 5nA (600nA maximum at 3.6V/85°C).
In OFFMode all Atmel ATA5830 AVR® Ports PB0..PB7 and PC0..PC5 are switched to Input. PC0..PC5 and PB7 have
internal pull-up resistors ensuring that the voltage at these ports is VS. PB0..PB6 are tristate inputs and require additional
consideration. PB1,PB2 and PB5 have defined voltages since they are connected to the output of the external
microcontroller. PB4 is connected to ground to avoid unwanted power ups. PB0, PB3 and PB6 do not require external
circuitry since the internal circuit avoids transverse currents in the OffMode. The external microcontroller has to tolerate the
floating inputs. Otherwise additional pull down resistors are required on these floating lines.
Typically, the key fob buttons are connected to the external microcontroller and the Atmel ATA5830 wake-up is done by
pulling NSS (pin 27) and NPWRON1 (pin 15) to ground. If there are not enough ports for button inputs on the microcontroller,
it is possible to connect up to four additional buttons to the Ports PC2..PC5. In this case, the occurrence of a port event
(button pressed) will generate an interrupt (pin 28). The port event that triggered the interrupt is available in the event
register.
In this type of application a PCB trace loop antenna is typically used. An internal antenna tuning procedure tunes the
resonant frequency of this loop antenna to the TX frequency. This is accomplished with an integrated variable capacitor on
the ANT_TUNE pin. RF_OUT and RF_IN are optimally matched to the SPDT_TX and SPDT_RX pins of the integrated
RX/TX switch. The SPDT_ANT pin has an impedance of 50Ω for both the RX and TX functions. The DC output voltage of the
power amplifier is required at the SPDT_TX pin for proper operation. Also, the RFIN pin needs a DC path to ground, which is
easily achieved with the matching shunt inductor. The impedance of the loop antenna is transformed to 50Ω with three
capacitors, two of them external and one built into the Atmel ATA5830 on the ANT_TUNE pin.
An external crystal, together with the fractional-N PLL within the Atmel ATA5830 is used to fix the RX and TX frequency.
Accurate load capacitors for this crystal are integrated, to reduce system part count and cost. Only four supply blocking
capacitors are needed to decouple the different supply voltages AVCC, DVCC, VS and VS_PA of the Atmel ATA5830. The
exposed die pad is the RF and analog ground of the Atmel ATA5830. It is directly connected to AGND via a fused lead. For
applications operating in the 868.3MHz or 915MHz frequency bands, a high band RF input is supplied, RFIN_HB, and must
be used instead of RFIN_LB.
ATA5830/ATA5830N [SUMMARY DATASHEET]
7
9208FS–RKE–06/13
5秒后页面跳转
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