Rainbow-electronics MAX1401 Manual do Utilizador descarregar pdf (Página 34)

Loop-Powered, 4–20mA Transmitters

Low power, single-supply operation, and easy interfac-

ing with optocouplers make the MAX1401 ideal for

loop-powered 4–20mA transmitters. Loop-powered

transmitters draw their power from the 4–20mA loop,

limiting the transmitter circuitry to a current budget of

4mA. Tolerances in the loop further limit this current

budget to 3.5mA. Since the MAX1401 consumes only

250µA, a total of 3.25mA remains to power the remain-

ing transmitter circuitry. Figure 16 shows a block dia-

gram for a loop-powered 4–20mA transmitter.

Power Supplies

No specific power sequence is required for the

MAX1401; either the V+ or the V

supply can come

up first. While the latchup performance of the MAX1401

is good, to avoid latchup it is important that power be

applied to the MAX1401 before the analog input signals

(AIN_) or the CLKIN inputs. If this is not possible, then

the current flow into any of these pins should be limited

to 50mA. If separate supplies are used for the

MAX1401 and the system digital circuitry, then the

MAX1401 should be powered up first.

MAX1401

+3V, 18-Bit, Low-Power, Multichannel,

Oversampling (Sigma-Delta) ADC

34 ______________________________________________________________________________________

DAC

GAIN

OFST

IN+

IN-

SENSE

4–20mA LOOP

INTERFACE

FDBK

ISOLATION

BARRIER

V+

GND

V+

SPI

GND

SENSOR

VOLTAGE

REGULATOR

µP/µC

MAX1401

Figure 16. 4–20mA Transmitter

+3V

+1.25V

REFIN+

REFIN-

AGND

DGND

THERMOCOUPLE

JUNCTION

SWITCHING

NETWORK

PGA

BUFFER

AIN1

AIN2

MAX1401

Figure 15. Thermocouple Application with MAX1401

1 2 ... 29 30 31 32 33 34 35 36

Comentários a estes Manuais

Sem comentários

Rainbow-electronics MAX1401 Manual do Utilizador Página 34

Comentários a estes Manuais

Manuais e produtos relacionados com Sensores Rainbow-electronics MAX1401