U2745B - Atmel Corporation

U2745B

Rev. A2, 28-Sep-00 1 (7)

UHF ASK Transmitter

Description

The U2745B is a PLL transmitter IC which has been

specially developed for the demands of RF low-cost data

transmission systems at data rates up to 20 kBaud.

The transmitting frequency range is 310 MHz to

440 MHz. It can be used in ASK systems. The main ap-

plications of the U2745B are in the areas of outside

temperature metering, socket control, garage door

opener, consumption metering, light/ fan or aircondition

control, jalousies, wireless keyboard and various other

consumer market applications.

Electrostatic sensitive device.

Observe precautions for handling.

Features

DSupply voltage 2.2 V to 4.0 V

in the temperature range –40°C to 85°C

DOne-chip solution with minimum external circuitry

DLower cost than the usual discrete solutions using

SAW and transistors

DVery small SSO16 package, pitch 0.635, 150 mil

D“Single-Ended Open-Collector” output (same anten-

nas can be used as in discrete solutions, simpler

adaptation of magnetic loop antennas)

DXTO output for clocking the C, thereby together

with M44C090 or M44C890 the optimum system

cost-effectiveness

DVery high transmitting frequency accuracy compared

to SAW solutions. This enables receivers at lower

bandwidth than is possible with SAW resonators.

DESD protection according to MIL-STD.883

(4KV HBM) except Pins XTO1/ 2, ANT and LF

System Block Diagram

Demod.

IF Amp

LNA VCO

PLL XTO

Control

U3745BM 1...3 mC

Power

amp.

XTO VCO

PLL

U2745B

Antenna Antenna

UHF ASK

Remote control transmitter UHF ASK

Remote control receiver

Encoder

M44Cx9x

1 Li cell

Keys

Figure 1. System block diagram

Order Information

Extended Type Number Package Remarks

U2745B-MFB SSO16 Tube

U2745B-MFBG3 SSO16 Taped and reeled

U2745B

Rev. A2, 28-Sep-002 (7)

Pin Description

VCC

CLK

GND

LFVCC

LFGND

ASK

PWRVCC

ANT

PWRGND1

PWRGND2

XTO1

n.c.

GND

PWRSET

U2745B

Figure 2. Pinning SSO16

Pin Symbol Function

1 ASK Modulation input ASK

2 EN Enable input

3 VCC Supply voltage

4 CLK Clock output

5 GND Ground

6 LFVCC Supply voltage VCO

7 LFGND VCO ground

8 LF Circuit PLL loop

9 n.c. Not connected

10 XTO1 Connection for crystal

11 PWRGND2 Power GND2

12 PWRGND1 Power GND1

13 ANT RF output

14 PWRVCC Supply voltage power

amplifier

15 PWRSET Applied to VCC

16 GND Ground

Block Diagram

14919

Power

VCO

XTO

ASK

VCC

CLK

GND

LFVCC

LFGND

GND

PWRSET

PWRVCC

ANT

PWRGND1

PWRGND2

XTO1

n.c.

U2745B

Figure 3. Block diagram

U2745B

Rev. A2, 28-Sep-00 3 (7)

General Description

The fully integrated VCO and the “single-ended open-

collector” output allow particularly simple, low-cost RF

miniature transmitters to be assembled. The single-ended

output enables a considerably simplified adaptation of

both a magnetic loop antenna of any form or a /4

antenna. This is because the load impedance must not be

balanced as would be the case with a differential output.

The XTO’s frequency can be selected at 13.56 MHz or

USA 9.844 MHz. At these frequencies, crystals have a

very fast start-up time < 1.5 ms, whereby a wait time of

5 to 10 ms is required until the transmitter IC is locked.

This means that the processor does not need to poll a lock

detect output.

Functional Description

ASK Transmission

The U2745B is activated by EN = VS. VASK must remain

0 V for 5 ms, then the output power can be modulated by

means of Pin ASK. VEN remains = VS during transmis-

sion of the message. The ASK input activates the power

amplifier and the PLL.

Take-Over of the Clock Pulse in the µC

The clock of the crystal oscillator can be used for clocking

the µC. The M44C090 and M44C890 have the special

feature of starting with an integrated RC oscillator to

switch on the U2745B with VEN = VS. 5 ms later, the

3.39-MHz clock frequency is present, so that the message

can be sent with crystal accuracy.

Application Circuit

The following component values are recommendations

for a typical application. C4, C5, C6 are block capacitors.

The values of these capacitors depend on the board

layout. C 4 = 1 n F, C 5 = 1 nF, C6 = 22 nF are typically used

here. For C5, the impedance between f = 100 MHz and

f = 1 GHz should be as low as possible.

CLoop1, CLoop2 are selected so that the antenna

oscillates in resonance and the adaptation to the

appropriate impedance transformation is possible.

LFeed is an inductor for the antenna’s DC current supply.

A typical value is LFeed = 220 nH. LFeed can be either

printed on the PC_Board or be a discrete component.

Further information regarding the application is provided

in the description of the “RKE Design Kit”.

Output Power Measurement

The following output network (see figure 4) can be used

for output power evaluation, the exact values of L10, C10

are dependent on the layout.

L10, C10 is the transformation network to adopt the

output impedance of the IC to 50  The following table

shows the values for an output power of 2 mW and an

RPWRSET = 1.2 k

f/ MHz C10/ pF L10/ nH ZLoad_opt/ 

315 2.7 56 260 + j330

433.92 1.8 33 185 + j268

15009

PWRVCC

ANT

L10

C10

50 

ZLoad-opt

Figure 4. Measurement output network

U2745B

Rev. A2, 28-Sep-004 (7)

161

Power

VCO

XTO

ASK

VCC

CLK

GND

LFVCC

LFGND

GND

PWRSET

PWRVCC

ANT

PWRGND1

PWRGND2

XTO1

n.c.

RPWRSET

LFeed

CLoop1

13.56MHz

+VS= 2.2...4.0V

CLoop2

ASK

CLK

3.39MHz

U2745B

Antenna

Figure 5. Application circuit

Absolute Maximum Ratings

Parameters Symbol Min. Typ. Max. Unit

Supply voltage VS6 V

Power dissipation Ptot 250 mW

Junction temperature Tj150 °C

Storage temperature Tstg –55 125 °C

Ambient temperature Tamb –40 85 °C

Thermal Resistance

Parameters Symbol Value Unit

Junction ambient RthJA 180 K/W

U2745B

Rev. A2, 28-Sep-00 5 (7)

Electrical Characteristics

All parameters are refered to GND (Pin 5), VS = 3 V, Tamb = 25°C, unless otherwise specified

The possible operating ranges refer to different circuit conditions: VS = 2.2 V to 4.0 V @ Tamb = –40°C to +85°C

Parameters Test Conditions / Pins Symbol Min. Typ. Max. Unit

Supply current (power down) VASK, VEN v 0.3 V, VS < 3.6 V ISoff 2 10 µA

Supply current

(power up, output OFF) VASK = GND, VEN = VS, Vs = 3 V ISon 4.7 6.2 mA

Supply current

(power up, output ON) VASK = VS, VS = 3 V

RPWRSET = 1.2 k

IStransmit 10 12.5 mA

Output power VS = 3 V, T amb = 25°C,

f = 433.92 MHz

RPWRSET = 1.2 kPRef 1 3 5 dBm

Output power variation for

f = 315 MHz compared to

f = 433.92 MHz

f = 315 MHz

Pout = PRef + PRef

PRef 1.5 dB

Maximum peak output

antenna voltage @Pout = 2.0 mW,

The load impedance must be selected

to meet the Vout maximum requirement.

The supply current is not dependent on

the load impedance tolerance.

Voutmax VS – 0.7 V V(peak)

Spurious emission fo ± n × fPC (fPC = 6.78 MHz)

Load capacitance at CLK ≤3 pF

f = 230 MHz to 470 MHz

f < 230 MHz, f > 470 MHz Em

Em –40

–58 dBC

dBC

Oscillator frequency XTO Crystal frequency = 13.56 MHz fXTO 13.56

– 50 ppm 13.56 13.56

+50 ppm MHz

Loop bandwidth For best LO noise

Loop filter components:

C2 = 3.9 nF, C1 = 15 nF, R4 = 220 

BLoop 100 kHz

Phase noise VCO @ 1 MHz

@ 36 MHz PNVCO

PNVCO

–90

–122 dBC/Hz

Frequency range of the VCO fVCO 310 440 MHz

Clock output

(CMOS µC compatible) Clkout fout/128 MHz

Load capacitance at CLK CCLK 10 pF

Series resonance R of the

crystal fXTO = 13.56 MHz

fXTO = 9.84 MHz Rs

Rs 80

100 



ASK modulation frequency

rate Duty cycle of the

modulation signal = 50% fmodASK 0 20 kHz

CLK output

– Output current Low

– Output current High

VCLK = 0.2 × VS

VCLK = 0.3 × VS

VCLK = 0.8 × VS

VCLK = 0.7 × VS

Iol

Ioh

150

200

–150

–200 100

A

U2745B

Rev. A2, 28-Sep-006 (7)

UnitMax.Typ.Min.SymbolTest Conditions / PinsParameters

ASK input

– Low level input voltage

– High level input voltage

– Input current High

VASKl

VASKh

IASKh

1.7 0.3

140

A

Enable ASK

– Low level input voltage

– High level input voltage

– Input current High

VEN

VFSKl

VFSKh

IFSKh

1.7 0.3

140

A

Package Information

13045

technical drawings

according to DIN

specifications

Package SSO16

Dimensions in mm 5.00

4.80

5.00 max

1.40

0.25

0.10

0.25 0.635

4.45

6.2

5.8

3.95 max

5.2

4.8

0.2

16 9

U2745B

Rev. A2, 28-Sep-00 7 (7)

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