Datasheet

DAC161P997

www.ti.com

SNAS515E –JULY 2011–REVISED OCTOBER 2013

Functional Overview

4-20 mA CURRENT LOOP TRANSMITTER

The DAC161P997 is a 16-bit DAC realized as a ∑Δ modulator. The DAC’s output is a current pulse train that is

filtered by the on-board low pass RC filter. The final output current is a multiplied copy of the filtered modulator

output. This architecture ensures an excellent linearity performance, while minimizing power consumption of the

device.

The DAC161P997 eases the design of robust, precise, long-term stable industrial systems by integrating all

precision elements on-chip. Only a few external components are needed to realize a low-power, high-precision

industrial 4 - 20 mA transmitter.

In case of a fault, or during initial power-up the DAC161P997 will output current in either upper or lower error

current band. The choice of band is user selectable via a device pin. The error current value is user

programmable via the SWIF link by the Master.

SINGLE-WIRE INTERFACE (SWIF)

SWIF is a versatile and robust solution for transmitting digital data over the galvanic isolation boundary using just

one isolation element: a pulse transformer.

Digital data format achieves the information transmission without the loss of fidelity which usually afflicts

transmissions employing PWM (Pulse Width Modulation) schemes. Digital transmission format also makes

possible data differentiation: user can specify whether given data word is a DAC input to be converted to loop

current, or it is a device configuration word.

SWIF was designed to use in conjunction with pulse transformer as an isolation element. The use of the

transformers to cross the isolation boundary is typical in the legacy systems due to their robustness, low-power

consumption, and low cost. However, system implementation is not limited to the transformer as a link since

SWIF easily interfaces with opto-couplers, or it can be directly driven by a CMOS gate.

SWIF incorporates a number of features that address robustness aspect of the data link design:

1. Bidirectional signal flow: the DAC161P997 can issue an ACKNOWLEDGE pulse back to the master transmitter, via the same physical

channel, to confirm the reception of the valid data;

2. Error Detection: SWIF protocol incorporates frame length detection and parity checks as a method of verifying the integrity of the

received data;

3. Channel Activity Detection: SWIF can monitor the data channel and raise an error flag should the expected activity drop below

programmable threshold, due to , for example, damage to the physical channel.

In the typical system the Master is a micro controller. SWIF has been implemented on a number of popular micro

controllers where it places minimum demands on the hardware or software resources even of the simple 8-bit

devices.

SWIF gives the system designer flexibility is balancing the trade-offs between the data rate, activity monitoring

functionality and the power consumption in the transformer coupled data channel. At lowest data rates, with long

inactive inter-frame periods, the power consumed by SWIF is negligible. See Inter-Frame Period.

Product Folder Links: DAC161P997