Try Analog Devices AD421. It has a 4-20mA transducer (active or passive). My english is not so good, so I'll let speak Analog Devices. Hope this works for you: PRODUCT HIGHLIGHTS 1. The AD421 is a single chip, high performance, low cost solution for generating 4 mA to 20 mA signals for smart industrial control transmitters. 2. The AD421âs regulated supply voltage can be used to power any additional circuits in the transmitter. The regulated output value is pin selectable as either +3 V, +3.3 V or +5 V. 3. The AD421âs on-chip references can provide a precision reference voltage to other devices in the system. This refer-ence voltage can be either +1.25 V or +2.5 V. 4. The AD421 is fully compatible with standard HART cir-cuitry or other similar FSK protocols. 5. With the addition of a single discrete transistor, the AD421 can be operated from VCC + 2 V min to a maximum of the breakdown voltage of the pass transistor. 6. The AD421 converts the digital data to current with 16-bit resolution and monotonicity. Full-scale settling time to ±0.1% typically occurs within 8 ms. 7. The AD421 features a programmable alarm current capabil-ity that allows the transmitter to send out of range currents to indicate a transducer fault. HART is a registered trademark of the HART Communication Foundation. -----Mensaje original----- De: Harrison Cooper Para: PICLIST@MITVMA.MIT.EDU Fecha: viernes, 07 de mayo de 1999 14:52 Asunto: single chip solution ( 0-5V --> 4-20mA ) >sums it up. Someplace I thought I had read/heard/seen a single chip that >would do this. Sure, do it with an opamp, but I want a KISS solution, single >part with all the resistors, etc on the internal etch, and guaranteed to >drive an industrial 4-20mA device. >