DESCRIPTION

The LTC2635 is a family of quad 12-, 10-, and 8-bit voltage-output DACs with an integrated, high-accuracy, low-drift reference in a 16-pin QFN or a 10-lead MSOP package. It has rail-to-rail output buffers and is guaranteed monotonic. The LTC2635-L has a full-scale output of 2.5V, and operates from a single 2.7V to 5.5V supply. The LTC2635-H has a full-scale output of 4.096V, and operates from a 4.5V to 5.5V supply. Each DAC can also operate with an external reference, which sets the fullscale output to the external reference voltage. These DACs communicate via a 2-wire I2C-compatible serial interface. The LTC2635 operates in both the standard mode (clock rate of 100kHz) and the fast mode (clock rate of 400kHz). The LTC2635 incorporates a power-on reset circuit. Options are available for reset to zero-scale, reset to mid-scale in internal reference mode, reset to mid-scale in external reference mode, or reset with all DAC outputs in a high-impedance state after power-up.

 

FEATURES

Integrated Precision Reference

4.096V Full-Scale 10ppm/°C (LTC2635-H)

Maximum INL Error: ±2.5 LSB (LTC2635-12)

Power-On-Reset to Zero-Scale/Mid-Scale/Hi-Z

Low Noise: 0.75mVP-P 0.1Hz to 200kHz

Guaranteed Monotonic Over –40°C to 125°C Automotive Temperature Range

Selectable Internal or External Reference

Ultralow Crosstalk Between DACs (3nV•s)

Low Power: 0.6mA at 3V

Double-Buffered Data Latches

Small 16-Pin 3mm × 3mm QFN and 10-Lead MSOP Packages

 

APPLICATIONS

Mobile Communications

Process Control and Industrial Automation

Power Supply Margining

Portable Equipment

Automotive

 

OPERATION

The LTC2635 is a family of quad voltage output DACs in 16-pin QFN and 10-lead MSOP packages. Each DAC can operate rail-to-rail using an external reference, or with its full-scale voltage set by an integrated reference. Eighteen combinations of accuracy (12-, 10-, and 8-bit), power-on reset value (zero-scale, mid-scale in internal reference mode, or mid-scale in external reference mode), DAC power-down output load (high impedance or 200kΩ), and full-scale voltage (2.5V or 4.096V) are available. The LTC2635 is controlled using a 2-wire I2C interface.

Power-On Reset

The LTC2635-HZ/-LZ clear the output to zero-scale when power is first applied, making system initialization con-sistent and repeatable.

For some applications, downstream circuits are active during DAC power-up, and may be sensitive to nonzero outputs from the DAC during this time. The LTC2635 contains circuitry to reduce the power-on glitch: the analog output typically rises less than 5mV above zero-scale during power on. In general, the glitch amplitude decreases as the power supply ramp time is increased.

The LTC2635-HMI/-LMI/-LMX provide an alternative reset, setting the output to mid-scale when power is first applied. The LTC2635-LMI and LTC2635-HMI power up in internal reference mode, with the output set to a mid-scale voltage of 1.25V and 2.048V, respectively. The LTC2635-LMX power-up in external reference mode, with the output set to mid-scale of the external reference. The LTC2635-LMO powers up in internal reference mode with all the DAC channels placed in the high-impedance state (powered-down). Input and DAC registers are set to the mid-scale code, and only the internal reference is powered up, causing supply current to be typically 100µA upon power up.

Power-Down Mode

For power-constrained applications, power-down mode can be used to reduce the supply current whenever less than four DAC outputs are needed. When in power-down, the buffer amplifiers, bias circuits, and integrated reference circuits are disabled, and draw essentially zero current. The DAC amplifier outputs are put into a high-impedance state, and the output pins are passively pulled to ground through individual 200k resistors (LTC2635-LMI/-LMX/ -LZ/-HMI/-HZ). For the LTC2635-LMO options, the output pins are not passively pulled to ground, but are also placed in a high-impedance state (open-circuited state) during power-down, typically drawing less than 0.1µA. The LTC2635-LMO options power-up with all DAC outputs in this high-impedance state. They remain that way until