LTC2636 datasheet(17/24 Pages) AD

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LTC2636

Rev D

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OPERATION

The LTC2636 is a family of octal voltage output DACs in

14-lead DFN and 16-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 refer-

ence mode, or mid-scale in external reference mode),

and full-scale voltage (2.5V or 4.096V) are available. The

LTC2636 is controlled using a 3-wire SPI/MICROWIRE

compatible interface.

Power-On Reset

The LTC2636-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 LTC2636

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.

See “Power-On Reset Glitch” in the Typical Performance

Characteristics section.

The LTC2636-HMI/-HMX/-LMI/-LMX provide an alterna-

tive reset, setting the output to mid-scale when power is

first applied. The LTC2636-LMI and LTC2636-HMI power

up in internal reference mode, with the output set to a

mid-scale voltage of 1.25V and 2.048V respectively. The

LTC2636-LMX and LTC2636-HMX power-up in external

reference mode, with the output set to mid-scale of the

external reference. Default reference mode selection is

described in the Reference Modes section.

Power Supply Sequencing

The voltage at REF (Pin 9-DFN, Pin 11-MSOP) must be

kept within the range –0.3V ≤ VREF ≤ VCC + 0.3V (see

Absolute Maximum Ratings). Particular care should be

taken to observe these limits during power supply turn-

on and turn-off sequences, when the voltage at VCC is in

transition.

Transfer Function

The digital-to-analog transfer function is:

VOUT(IDEAL) =

⎛

⎝

⎜

⎞

⎠

⎟VREF

where k is the decimal equivalent of the binary DAC

input code, n is the resolution, and VREF is either 2.5V

(LTC2636-LMI/-LMX/-LZ) or 4.096V (LTC2636-HMI/-

HMX/-HZ) when in Internal Reference mode, and the

voltage at REF when in External Reference mode.

Table 1. Command Codes

COMMAND*

Write to Input Register n

Update (Power-Up) DAC Register n

Write to Input Register n, Update (Power-Up) All

Write to and Update (Power-Up) DAC Register n

Power-Down DAC n

Power-Down Chip (All DAC’s and Reference)

Select Internal Reference (Power-Up Reference)

Select External Reference (Power-Down Internal

Reference)

No Operation

*Command codes not shown are reserved and should not be used.

Table 2. Address Codes

ADDRESS (n)*

DAC A

DAC B

DAC C

DAC D

DAC E

DAC F

DAC G

DAC H

ALL DACS

*Address codes not shown are reserved and should not be used.

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