Rainbow Electronics ATA5757 User Manual

Features

• PLL Transmitter IC with Single-ended Output

• High Output Power (6 dBm) at 8.1 mA (315 MHz) and 8.5 mA (433 MHz) Typical Values

• Divide by 24 (ATA5756) and 32 (ATA5757) Blocks for 13 MHz Crystal Frequencies and

for Low XTO Start-up Times

• Modulation Scheme ASK/FSK with Internal FSK Switch

• Up to 20 kBaud Manchester Coding, Up to 40 kBaud NRZ Coding

• Power-down Idle and Power-up Modes to Adjust Corresponding Current Consumption

through ASK/FSK/Enable Input Pins

• ENABLE Input for Parallel Usage of Controlling Pins in a 3-wire Bus System

• CLK Output Switches ON if the Crystal Current Amplitude has Reached 35% to 80% of

its Final Value

• Crystal Oscillator Time Until CLK Output is Activated, Typically 0.6 ms

• Supply Voltage 2.0 V to 3.6 V in Operation Temperature Range of -40° C to 125° C

• ESD Protection at all Pins (4 kV HBM)

• Small Package MSOP10

Benefits

• Low Parasitic FSK Switch Integrated

• Very Short and Reproducable Time to Transmit Typically <0.85 ms

• 13.125 MHz/13.56 MHz Crystals Give Opportunity for Small Package Sizes

UHF ASK/FSK Transmitter

ATA5756 ATA5757

Description

The ATA5756/ATA5757 is a PLL transmitter IC which has been developed for the demands of RF low-cost transmission systems at data rates up to 20 kBaud Manchester coding and 40 kBaud NRZ coding. The transmitting frequency range is 313 MHz to 317 MHz (ATA5756) and 432 MHz to 448 MHz (ATA5757), repectively. It can be used in both FSK and ASK systems. Due to its shorten crystal oscillator settling time it is well suited for Tire Pressure Monitoring (TPM) and for Passive Entry Go applications.

Figure 1. System Block Diagram

UHF ASK/FSK

1 Li cell

Keys

Encoder

ATARx9x

TPM and Remote control

transmitter

ATA5756/

ATA5757

PLL

XTO

VCO

Power

amp.

Antenna Antenna

U3741B/ U3745B/ T5743/

T5744/

LNA VCO

UHF ASK/FSK

Remote control receiver

Demod.

IF Amp

PLL XTO

Control

1...3

µC

Preliminary

Rev. 4702D–RKE–02/04

Pin Configuration

Figure 2. Pinning MSOP10

CLK

ASK

FSK

ANT2

5ANT1

ATA5756 ATA5757

ENABLE

GND

XTO1

XTO2

Pin Description

Pin Symbol Function Configuration

Clock output signal for the microcontroller. The clock output frequency is set by the crystal to f

1CLK

The CLK output stays Low in powerdown mode and after enabling of the PLL. The CLK output switches on if the oscillation amplitude of the crystal has reached a certain level.

XTAL

/8.

100

CLK

200k

2ASK

3FSK

ATA5756/ATA5757 [Preliminary]

Switches on the power amplifier for ASK modulation and enables the PLL and XTO if the ENABLE pin is open

Switches off the FSK switch (switch has high Z if signal at pin FSK is High) and enables the PLL and the XTO if the ENABLE pin is open

ASK

FSK

200k

50k

200k

20 µA

= 1.1V

Ref

= 1.1V

Ref

5 µA

4702D–RKE–02/04

ATA5756/ATA5757 [Preliminary]

Pin Description

Pin Symbol Function Configuration

4 ANT2 Emitter of antenna output stage

5 ANT1 Open collector antenna output

ANT1

ANT2

210 µA

1.2k

6 XTO2 Diode switch, used for FSK modulation

7 XTO1 Connection for crystal

(FSK < 0.25V)

AND

(ENABLE > 1.7V)

XTO2

1.5k

XTO1

182 µA

8 VS Supply voltage See ESD protection circuitry (see Figure 12) 9 GND Ground See ESD protection circuitry (see Figure 12)

ENABLE input

30 µA

10 ENABLE

4702D–RKE–02/04

If ENABLE is connected to GND and the ASK or FSK pin is High, the device stays in idle mode. In normal operation ENABLE is left open and ASK or FSK is used to enable the device.

ENABLE

(FSK >1.7 V ) OR

(ASK > 1.7 V)

150k

250k

Figure 3. Block Diagram

ATA5756 /

ATA5757

CLK

ASK

Power up/down

24/ 32

ENABLE

GND

FSK

ANT2

ANT1

5 6

PLL

PFD

VCO

XTO

Ampl. OK

XTO1

XTO2

General Description This fully integrated PLL transmitter allows the design of simple, low-cost RF miniature

transmitters for TPM and RKE applications. The VCO is locked to 24 × f for ATA5756/ATA5757. Thus, a 13.125 MHz/13.56 MHz crystal is needed for a 315 MHz/433.92 MHz transmitter. All other PLL and VCO peripheral elements are integrated.

XTAL

/32 × f

XTAL

The XTO is a series resonance (current mode) oscillator. Only one capacitor and a crystal connected in series to GND are needed as external elements in an ASK system. The internal FSK switch, together with a second capacitor, can be used for FSK modulation.

The crystal oscillator needs typically 0.6 ms until the CLK output is activated if a crystal as defined in the electrical characteristics is used (e.g., TPM crystal). For most crystals used in RKE systems, a shorter time will result.

The CLK output is switched on if the amplitude of the current flowing through the crystal has reached 35% to 80% of its final value. This is synchronized with the 1.64/1.69 MHz CLK output. As a result, the first period of the CLK output is always a full period. The PLL is then locked <250 µs after CLK output activation. This means an additional wait time of ≥250 µs is necessary before the PA can be switched on and the data transmission can start. This results in a significantly lower time of about 0.85 ms between enabling the ATA5756/ATA5757 and the beginning of the data transmission which saves battery power especially in tire pressure monitoring systems.

ATA5756/ATA5757 [Preliminary]

4702D–RKE–02/04

ATA5756/ATA5757 [Preliminary]

The power amplifier is an open-collector output delivering a current pulse which is nearly independent from the load impedance and can therefore be controlled via the connected load impedance.

This output configuration enables a simple matching to any kind of antenna or to 50 Ω. A high power efficiency for the power amplifier results if an optimized load impedance of Z

Load, opt

=380Ω + j340 Ω (ATA5756) at 315 MHz and Z

(ATA5757) at 433.92 MHz is used at the 3-V supply voltage.

Load, opt

=280Ω +j310Ω

Functional Description

If ASK = Low, FSK = Low and ENABLE = open or Low, the circuit is in power-down mode consuming only a very small amount of current so that a lithium cell used as power supply can work for many years.

If the ENABLE pin is left open, ENABLE is the logical OR operation of the ASK and FSK input pins. This means, the IC can be switched on by either the FSK of the ASK input.

If the ENABLE pin is Low and ASK or FSK are High, the IC is in idle mode where the PLL, XTO and power amplifier are off and the microcontroller ports controlling the ASK and FSK inputs can be used to control other devices. This can help to save ports on the microcontroller in systems where other devices with 3-wire interface are used.

With FSK = High and ASK = Low and ENABLE = open or High, the PLL and the XTO are switched on and the power amplifier is off. When the amplitude of the current through the crystal has reached 35% to 80% of its final amplitude, the CLK driver is automatically activated. The CLK output stays Low until the CLK driver has been activated. The driver is activated synchronously with the CLK output frequency, hence, the first pulse on the CLK output is a complete period. The PLL is then locked within <250 µs after the CLK driver has been activated, and the transmitter is then ready for data transmission.

With ASK = High the power amplifier is switched on. This is used to perform the ASK modulation. During ASK modulation the IC is enabled with the FSK or the ENABLE pin.

With FSK = Low the switch at pin XTO2 is closed, with FSK = High the switch is open. To achieve a faster start-up of the crystal oscillator, the FSK pin should be High during start-up of the XTO because the series resistance of the resonator seen from pin XTO1 is lower if the switch is off.

4702D–RKE–02/04

The different modes of the ATA5756/ATA5757 are listed in Table 1, the corresponding current consumption values can be found in the table “Electrical Characteristics” on page 15.

Table 1. ATA5756/ATA5757 Modes

ASK Pin FSK Pin ENABLE Pin Mode

Low Low Low/open Power-down mode, FSK switch High Z

Low Low High Power-up, PA off, FSK switch Low Z

Low High High/open Power-up, PA off, FSK switch High Z

High Low High/open Power-up, PA on, FSK switch Low Z

High High High/open Power-up, PA on, FSK switch High Z

Low/High High Low Idle mode, FSK switch High Z

High Low/High Low Idle mode, FSK switch High Z

Transmission with ENABLE = open

ASK Mode The ATA5756/ATA5757 is activated by ENABLE = open, FSK = High, ASK = Low. The

microcontroller is then switched to external clocking. After typically 0.6 ms, the CLK driver is activated automatically (i.e., the microcontroller waits until the XTO and CLK are ready). After another time period of The output power can then be modulated by means of pin ASK. After transmission, ASK is switched to Low and the microcontroller returns back to internal clocking. Then, the ATA5756/ATA5757 is switched to power-down mode with FSK = Low.

Figure 4. Timing ASK Mode with ENABLE not Connected to the Microcontroller

≤250 µs, the PLL is locked and ready to transmit.

FSK

ASK

CLK

Power-down

∆T

XTO

Power-up,

PA off

> 250 µs

Power-up,

PA on (High)

Power-up,

PA off

(Low)

Power-down

FSK Mode The ATA5756/ATA5757 is activated by FSK = High, ASK = Low. The microcontroller is

then switched to external clocking. After typically 0.6 ms, the CLK driver is activated automatically (i.e., the microcontroller waits until the XTO and CLK are ready. After another time period of

≤250 µs, the PLL is locked and ready to transmit. The power

amplifier is switched on with ASK = H. The ATA5756/ATA5757 is then ready for FSK modulation. The microcontroller starts to switch on and off the capacitor between the crystal load capacitor and GND by means of pin FSK, thus, changing the reference frequency of the PLL. IF FSK = L the output frequency is lower, if FSK = H output frequency is higher. After transmission, FSK stays High and ASK is switched to Low and the microcontroller returns back to internal clocking. Then, the ATA5756/ATA5757 is switched to power-down mode with FSK = Low.

Figure 5. Timing FSK Mode with ENABLE not Connected to the Microcontroller

∆T

XTO

FSK

ASK

CLK

Power-down

ATA5756/ATA5757 [Preliminary]

Power-up,

PA off

> 250 µs

Power-up,

PA on

= High)

Power-up,

PA off

= Low)

Power-down

4702D–RKE–02/04

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