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Model TT339-0700
4-Wire Isolated Frequency Transmitter w/USB
Acromag, Inc. Tel: 248-295-0880
[
24
]
http://www.acromag.com
BLOCK DIAGRAM
How It Works
Key Points of Operation
DC Powered
Isolated Power
Isolated Input
Isolated Output
Input circuit is common to
USB ground
Universal output, current
or voltage
The TT339 transmitter uses a 32-bit microcontroller to measure the input signal and
transmit the digital measurement to the SPI bus. The SPI bus passes through digital
isolators and is received by an output DAC which drives a universal output driver for
current or voltage. The output is very unique in that it may drive current or voltage
to the load without having to change load connections. The output type and range
are user-configured. Power for the isolated input and isolated output circuits is
provided via an isolated flyback converter that operates on voltage wired to the
power terminals at TB4, or wired to optional bus power terminals along the DIN rail.
The input/USB, output, and power circuits are all isolated from each other. This
transmitter does not draw power from USB. The USB port ground is common to the
input circuit ground. The USB port ground of most PC’s is also common to the USB
cable shield and earth ground. Input sensors could be grounded or ungrounded. For
this reason, it is recommended that USB signals be isolated when connected to a PC
to prevent a ground loop from occurring between the PC earth ground and a
grounded input sensor, which would have the negative affect of pulling the input
bias supply to ground and clipping any negative range.
UNIVERSAL
16-BIT DAC
2.5V
REF
OUTPUT
DRIVER
MOSI
CLK
OSEL
MISO
DSEL
ERR
SPI
SPI
5V
15V
-15V
SPI
47.5
+
OUT+
TB3
OUT-
-
-
BUCK
REG
+5V
ISOLATED FLYBACK CONVERTER
PO+
PO+
5V
BIPOLAR
CONVERTER
PO+
-15V
+15V
BOOST
ISOLATED OUTPUT CIRCUIT
MICROCONTROLLER
USB
PORT
3.0V
5V
VX
FLYBACK
CONVERTER
P+
P-
12-32V
TB4
P-
4
+
5
-
3
+
2
+
1
+
NC
NC
NC
BUS CONN
ISOLATED POWER
ISOLATED POWER
VX
+5V
LDO
+5V
ISOLATED INPUT CIRCUIT
OUTPUT POWER
INPUT POWER
TT339-0700 SIMPLIFIED SCHEMATIC
(FILTERING AND DETAIL OMITTED FOR CLARITY)
FREQUENCY OR PULSE INPUT
DC CURRENT OR DC VOLTAGE OUTPUT
ISOLATED OUTPUT CIRCUIT
3
4
TB1
5
TB2
6
COM
COM
MODE
PDN
PUP
EXC_EN
10
11
12
7
8
9
+EXC
COM
+6V
EXC_EN
+5V EXC
VOLTAGE
REG.
+FINP
-FRTN
1
2
+5V
PUP
2.7K
1K
+5V
MODE
OPAMP
+5V
PULL
UP
INP. DIVIDER
UNI/BIPOLAR
V-REF
PULL
PDN
DOWN