LTC1454I データシートの表示（PDF） - Linear Technology

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LTC1454I

Dual 12-Bit Rail-to-Rail Micropower DACs

Linear Technology 

LTC1454/LTC1454L

U

OPERATIO

Serial Interface

The data on the DIN input is loaded into the shift register

on the rising edge of the clock. Data is loaded as one 24-bit

word, DAC A first, then DAC B. The MSB is loaded first for

each DAC. The DAC registers load the data from the shift

register when CS/LD is pulled high. The CLK is disabled

internally when CS/LD is high. Note: CLK must be low

before CS/LD is pulled low to avoid an extra internal clock

pulse.

The buffered output of the 24-bit shift register is available

on the DOUT pin which swings from ground to VCC.

Multiple LTC1454/LTC1454Ls may be daisy-chained to-

gether by connecting the DOUT pin to the DIN pin of the next

chip, while the CLK and CS/LD signals remain common to

all chips in the daisy-chain. The serial data is clocked to all

of the chips, then the CS/LD signal is pulled high to update

all of them simultaneously.

Reference

The LTC1454L has an internal reference of 1.22V with a full

scale of 2.5V (gain of 2 configuration). The LTC1454

includes an internal 2.048V reference, making 1LSB equal

to 1mV (gain of 2 configuration). When the buffer gain is

2, the external reference must be less than VCC/2 and be

capable of driving the 15k minimum DAC resistor ladder.

With a gain of 1 configuration the external reference must

be less than VCC – 1.5V.

Voltage Output

The rail-to-rail buffered output of the LTC1454 family can

source or sink 5mA when operating with a 5V supply while

pulling to within 300mV of the positive supply voltage or

ground. The output swings to within a few millivolts of

either supply rail when unloaded and has an equivalent

output resistance of 40Ω when driving a load to the rails.

The output can drive 1000pF without going into oscilla-

tion.

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