TSS721A

METER-BUS TRANSCEIVER
SLAS 222 - April 1999

D PACKAGE
• Meter-Bus Transceiver (TOP VIEW)
(for Slave) meets standard EN1434-3
• Receiver logic with dynamic level recognition BUSL2 BUSL1
• Adjustable constant current sink via resistor VB GND
• Polarity independent STC RIS
• Power fail function RIDD RXI

• Module supply voltage switch

PF RX

• 3.3 V constant voltage source

SC VDD

•
TXI VS
Remote powering TX BAT
• Up to 9600 baud in half duplex
for UART protocol

• Slave Power Support

- supply from Meter-Bus via output VDD
- supply from Meter-Bus via output VDD
or from back up battery
- supply from battery – Meter-Bus active
for data transmission only

description

TSS721A is a single chip transceiver developed for Meter-Bus standard (EN1434-3) applications.

The TSS721A interface circuit adjusts the different potentials between a slave system and the Meter-
Bus master. The connection to the Bus is polarity independent and supports full galvanic slave
isolation with opto-couplers.

The circuit is supplied by the master via the bus. Therefore this circuit offers no additional load for the
slave battery. A power-fail function is integrated.

The receiver has dynamic level recognition, and the transmitter a programmable current sink.

A 3.3-V voltage regulator, with power reserve for a delayed switch off at bus fault, is integrated.

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TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

function (the functional description refers to typical values)

Data Transmission Master to Slave

The mark level on the bus lines VBUS = MARK is defined by the difference of BUSL1 and BUSL2
at the slave. It is dependent on the distance of Master to Slave, which affects the voltage drop on
the wire. To make the receiver independent, a dynamic reference level on the SC pin is used for
the voltage comparator TC3 (refer to figure 1).

V BUS
I BUS I BUS
VB to IC V MARK = 20.8 .. 42 V

VT
V SPACE = V MARK - 10 V

BUSL1
TX
TC3 I BUS = constant
BR TXI
I SCcharge
BUSL2 SC
V TX
I SCdischarge

C SC

GND
V TXI

C BUSL1-BUSL2 = 30 pF typ.

at: VB = 25 V; fmeas = 1MHz

Figure 1

A capacitor CSC at pin SC is charged by a current ISCcharge and is discharged with a current
ISCdischarge where:
ISCcharge
ISCdischarge =
40 (typ.)

This ratio is necessary to run any kind of UART protocol independent of the data contents.
(e. g. if an 11-Bit UART protocol is transmitted with all data bits at '0' and only the stop bit at '1').
There must be sufficient time to recharge the capacitor CSC. The input level detector TC3 detects
voltage modulations from the master, VBUS = SPACE/MARK conditions and switches the inverted
output TXI and the non-inverted output TX.

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 TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

Data Transmission Slave to Master

The device uses current modulation to transmit information from Slave to the Master while the
bus voltage remains constant. The current source CS3 modulates the bus current and the master
detects the modulation. The constant current source CS3 is controlled by the inverted input RXI
or the non-inverted input RX. The current source CS3 can be programmed by an external resistor
RRIS. The modulation supply current IMS flows in addition to the current source CS3 during the
modulation time.

V RX
I BUS
VB to IC

ICS3 IMS

V RXI

BUSL1
CS3
RX
BR TC4
RXI
BUSL2 RIS V BUS
I BUS

V BUS = constant
R RIS

GND I SPACE
I MC I MARK

Figure 2

IMC = IMS + ICS3

Since the TSS721A is configured for half-duplex only, the current modulation from RX or RXI is
repeated concurrently as ECHO on the outputs TX and TXI. If the Slave, as well as the Master, is
trying to send information via the lines, the added signals appear on the outputs TX and TXI
which indicate the data collision to the slave (refer to figure 6).

The bus topology requires a constant current consumption by each connected slave.

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TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

To calculate the value of the programming resistor RRIS, use the following formula:

IMC [mA]

VRIS VRIS
20 RRIS= =
ICS 3 IMC − IMS
15

10 VRIS - voltage on pin RIS

typical RRIS - programming resistor
ICS3 - programmable current
5
IMC - modulation current
IMS - modulation supply current
R RIS
(typical 220 µA)
0 0.1 0.2 0.5 1 [kOhm]

Figure 3

Slave Supply 3.3-V

The TSS721A has the 3.3-V voltage regulator. The output power of this voltage regulator is
supplied by the storage capacitor CSTC at pin STC. The storage capacitor CSTC at Pin STC is
charged with constant current ISTC_use from the current source CS1. The maximum capacitor
voltage is limited to REF1. The charge current ISTC has to be defined by an external resistor at
Pin RIDD.

The adjustment resistor RRIDD can be calculated using the following formula:

VRIDD VRIDD
RRIDD= 25 = 25
ISTC ISTC_use + ICI1

ISTC - current from current source CS1

ISTC _use - charge current for support capacitor
ICI - internal current
VRIDD - voltage on pin RIDD
RRIDD - value of adjustment resistor

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 TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

The voltage level of the storage capacitor CSTC is monitored with comparator TC1. Once the
voltage VSTC reaches VVDD_on, the switch SVDD connects the stabilised voltage VVDD to pin VDD.
VDD is turned off if the voltage VSTC drops below the VVDD_off level.

Voltage variations on the capacitor CSTC create bus current changes:

I BUS
[µ A] Example: Single Mode Bus Load

916

914

912

910

V STC

1 2 3 4 5 6 7 8 [V]

Figure 4

At a bus fault the shut down time of VDD (toff) in which data storage can be performed depends on
the system current IVDD and the value of capacitor CSTC. Refer to Figure 5, which shows a
correlation between the shut down of the bus voltage VBUS and VDD_off and toff for dimensioning
the capacitor.
The output VS is meant for slave systems which are driven by the bus energy, as well as from a
battery should the busline voltage fail. The switching of VS is synchronised with VDD and is
controlled by the comparator TC1. An external transistor at the output VS allows switching from
the Meter-Bus remote supply to battery.

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TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

POWER ON-OFF
V BUS

V VB = VSTC + 0.6 V typical threshold voltage

for power fail PF

t on
V STC

V DDon
V DDoff
t

V VS

V VDD

V PF t off

Figure 5
VSTC − VVDDoff
toff = CSTC
IVDD + ICI1

Power Fail Function

Owing to the rectifier bridge BR at the input, BUSL1 and BUSL2, the TSS721A is polarity
independent. The pin VB to ground (GND) delivers the bus voltage VVB less the voltage drop over
the rectifier BR. The voltage comparator TC2 monitors the bus voltage. If the voltage VVB >
VSTC + 0.6 V, then the output PF = '1'. The output level PF = '0' (power fail) provides a warning of
a critical voltage drop to the microcontroller to save the data immediately.

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 TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

functional schematic
VB
CS1 I CI2 I BUS

TC2 PF
RIDD I CS3
BAT
I STC VF
BUSL1
BR
I STC_use I CI1 BUSL2
STC
CS2
TX
TC3
TXI
VS
TC1 SC

I MS
I VDD
VDD
VVDD REF2 REF1 CS3 ECHO
RX
3.3V 1.3V 7V TC4
RXI
R VS
RIS
GND

Figure 6

pinning pin function

1 BUSL2 Meter-Bus
2 VB differential bus voltage after rectifier
3 STC support capacitor
4 RIDD current adjustment input
5 PF power fail output
6 SC sampling capacitor
7 TXI data output inverted
8 TX data output
9 BAT logic level adjust
10 VS switch for bus or battery supply output
11 VDD voltage regulator output
12 RX data input
13 RXI data input inverted
14 RIS adjust input for modulation current
15 GND ground
16 BUSL1 Meter-Bus

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TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

absolute maximum ratings

Voltage BUSL1 to BUSL2 |50| V
Input voltage at RX and RXI - 0.3 to 5.5 V
Input voltage at pin UBAT - 0.3 to 5.5 V
Operating junction temperature - 25 to 150 °C
Operating temperature free-air - 25 to 85 °C
Storage temperature - 65 to 150 °C
Power derating factor junction to ambient 8.0 mW/°C

recommended operating conditions

Parameter min max unit

Bus voltage Receiver 10.8 42.0 V
|BUSL2-BUSL1| Transmitter 12.0 42.0 V
VB voltage (receive mode) 9.3 V
RIDD Resistor 13 80 kΩ
RIS Resistor 100 Ω
VBAT, (see Note 1) 2.5 3.8 V
Operating free-air temperature -25 85 °C

NOTE: All voltage values are measured with respect to the GND terminal unless otherwise noted.
NOTE 1: VBATmax <= VSTC – 1V

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 TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

electrical characteristics at recommended ranges (unless otherwise noted)

Parameter Test conditions min typ max unit

V drop IBUS=3mA 1.5 V
Rectifier BR
V drop current RIDD=13 kΩ 1.8 V
source CS1
IBUS VSTC=6.5 V; IMC=0 mA 3.0 mA
RIDD=13 kΩ
VSTC=6.5 V; IMC=0 mA 1.5 mA
RIDD=30 kΩ
∆IBUS ∆VBUS=10 V; IMC=0 mA 2 %
RIDD=13 – 30 kΩ
ICC VSTC=6.5 V; IMC=0 mA; VBAT=3.8 V; 650 µA
RIDD=13 kΩ; (see Note 2)
ICI1 VSTC=6.5 V; IMC=0 mA; VBAT=3.8 V; 350 µA
RIDD=13 kΩ; VBUS=6.5 V; RX/RXI=off
(See Note 2)
IBAT -0.5 0.5 µA
IBAT + IVDD VBUS=0 V; VSTC=0 V - 0.5 0.5 µA
VVDD -IVDD=1 mA; VSTC=6.5 V 3.1 3.4 V
RVDD -IVDD=2 to 8 mA; VSTC=4.5V 5.0 Ω
VSTC VDD=on and VS=on 5.6 6.4 V
VDD=off and VS=off 3.8 4.3 V
VSTC (See Note 3) 6.5 7.5 V
ISTC_use RIDD=30 kΩ; VSTC=5 V 0.65 1.1 mA
RIDD=13kΩ; VSTC=5 V 1.85 2.4 mA
VRIDD RIDD=30 kΩ; 1.23 1.33 V
VVS VDD=on; IVS=-5 µA VSTC VSTC V
-0.4
RVS VDD=off 0.3 1.0 MΩ
VPF VSTC= VVB=VSTC+0.8 V IPF= VBAT- VBAT V
6.5V -100 µA 0.6
VVB=VSTC+0.3 V IPF=1 µA 0 0.6 V
IPF=5 µA 0 0.9 V
t on CSTC = 50 µF, (see Note 4) 3 s

NOTE: All voltage values are measured with respect to the GND terminal unless otherwise noted.
NOTES: 2. Inputs RX/RXI and outputs TX/TXI are open; ICC = ICI1 + ICI2
3. IVDD < ISTC_use
4. Bus voltage slew rate: 1V/µs

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TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

electrical characteristics at recommended ranges (unless otherwise noted)

RECEIVER SECTION

Parameter test conditions min typ max unit

VT MARK MARK V
- 8.2 - 5.7
VSC VVB V
ISCcharge VSC=24 V; VVB=36 V -15 -40 µA
ISCdischarge VSC=VVB=24 V 0.3 -0.033 x µA
ISCcharge
VOH (TX; TXI) ITX/ITXI=-100 µA VBAT VBAT V
See fig. 1 - 0.6
VOL (TX; TXI) ITX/ITXI=100 µA 0 0.5 V
ITX=1.1 mA 0 1.5 V
ITX; ITXI VTX=7.5; VVB=12V; 10 µA
VSTC=6.0V; VBAT=3.8V

TRANSMITTER SECTION

Parameter Test conditions min typ max unit

IMC RRIS=100 Ω 11.5 19.5 mA
VRIS RRIS=100 Ω 1.4 1.7 V
RRIS=1000 Ω 1.5 1.8 V
VIH (RX; RXI) See fig. 2 VBAT-0.8 5.5 V
See Note 5
VIL (RX; RXI) See fig. 2 0 0.8 V

IRX VRX=VBAT=3 V; -0.5 0.5 µA

VVB=VSTC=0 V
VRX=0 V; VBAT=3 V; -10 -40 µA
VSTC=6.5 V
IRXI VRXI=VBAT=3 V; 10 40 µA
VVB=VSTC=0 V
VRXI=VBAT=3 V; 10 40 µA
VSTC=6.5 V

NOTE: All voltage values are measured with respect to the GND terminal unless otherwise noted.
NOTE 5: VIHmax = 5.5 V is valid only for the following condition: VSTC>=6.5 V.

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 TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

APPLICATIONS
basic application circuit for using of support capacitor CSTC > 50 µF

Remote Supply
RL1
11 VDD BUSL1 1
9 BAT 220
10 VS
5 PF VB 2
12 RX
TSS721A
13 RXI RL2
8 TX BUSL2 16
SENSOR 7 TXI 220
C ST SYSTEM RIS SC GND RIDD STC
14 6 15 4 3
(e.g. MSP430)
T1

R RIS R RIDD
C SC + C STC

METER - BUS

Figure 7

RRIDD = 30 kΩ CSTC =< 220 µF single load 1UL

RRIDD = 13 kΩ CSTC =< 470 µF double load 2UL

NOTE: Used Transistor T1 e.g. BSS84.

basic application circuit for supply from battery

RL1
11 VDD BUSL1 1
9 BAT 220
10 VS
5 PF VB 2
12 RX
TSS721A
13 RXI RL2
8 TX BUSL2 16
SENSOR 7 TXI 220
+ BAT C SSC SYSTEM RIS SC GND RIDD STC
14 6 15 4 3
(e.g. MSP430)
R load R RIS R RIDD
C VDD
C SC + C STC

METER - BUS
Figure 8
CSSC - system stabilising capacitor RRIDD - slave-current adjustment resistor
CSTC - support capacitor RRIS - modulation-current resistor
CSC - sampling capacitor RL1, RL2 - protection resistors
CVDD - stabilising capacitor (100 nF) Rload - discharge resistor (100 kΩ recommended)
CSTC : CVDD > = 4:1

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TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

basic applications for different supply modes

Remote Supply
RL1
11 VDD BUSL1 1
9 BAT 220
10 VS
5 PF VB 2
12 RX
TSS721A
13 RXI RL2
8 TX BUSL2 16
SENSOR 7 TXI 220
C SSC SYSTEM RIS SC GND RIDD STC
14 6 15 4 3
(e.g. MSP430)
R RIS R RIDD

C SC + C STC

Remote Supply/Battery Support

RL1
11 VDD BUSL1 1
T1 9 BAT 220
10 VS
5 PF VB 2
12 RX
TSS721A
13 RXI RL2
8 TX BUSL2 16
SENSOR 7 TXI 220
+ BAT C SSC SYSTEM RIS SC GND RIDD STC
14 6 15 4 3
(e.g. MSP430)
R RIS R RIDD
C SC + C STC

Battery Supply 11
RL1
VDD BUSL1 1
9 BAT 220
10 VS
5 PF VB 2
12 RX
TSS721A
13 RXI RL2
8 TX BUSL2 16
SENSOR 7 TXI 220
+ BAT C SSC SYSTEM RIS SC GND RIDD STC
14 6 15 4 3
(e.g. MSP430)
R RIS R RIDD
Rload
C VDD C SC + C STC

METER - BUS

Figure 9

NOTE: Please watch RDSon of the transistor T1 (e.g. BSS84) at low level battery voltage.

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 TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

basic optocoupler application

R3
RXI RL1
11 VDD BUSL1 1
9 BAT 220
OC2 10 VS
SENSOR R1
5 PF VB 2
+ BAT C SSC
12 RX
TSS721A
SYSTEM R4
13
RXI RL2
8
(e.g. MSP430) TX BUSL2 16
7 220
TXI
RIS SC GND RIDD STC
OC1
TXI 14 6 15 4 3

R2
Rload R RIS RRIDD

C VDD C SC + C STC

METER - BUS

Figure 10

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TSS721A
METER-BUS TRANSCEIVER
SLAS 222 - April 1999

MECHANICAL DATA
D(R-PDSO-G**) PLASTIC SMALL OUTLINE PACKAGE

10.00
9.80

6.20 4.00
5.80 3.81

1.75 max
Seating
Plane

0.25 1.27 0.51 0.10

0.10 0.35

0.20 nom
NOTES:

A. All linear dimensions are in milimeters. o o

0 -8
B. This drawing is subject to change without notice.

C. Body dimensions do not include mold flash Gage Plane

or protrusion, not to exceed 0.15.

D. Four center pins are connected to die mount pad.

0.25
E. Falls within JEDEC MS-012.

1.12
MAX 0.40
MIN

Figure 11

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