TLC7225C datasheet(8/21 Pages) TI

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TLC7225C, TLC7225I

QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS

SLAS109B – OCTOBER 1996 – REVISED FEBRUARY 2001

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

specification ranges

For the TLC7225 to operate to rated specifications, the input reference voltage must be at least 4 V below the

power supply voltage at the VDD terminal. This voltage differential is the overhead voltage required by the output

amplifiers.

The TLC7225 is specified to operate over a VDD range from 12 V ± 5% to 15 V ± 10% (i.e., from 11.4 V to 16.5 V)

with a VSS of – 5 V ± 10%. Operation is also specified for a single supply with a VDD of 15 V ± 5%. Applying a

VSS of – 5 V results in improved zero-code error, improved output sink capability with outputs near AGND, and

improved negative-going settling time.

Performance is specified over the range of reference voltages from 2 V to (VDD – 4 V) with dual supplies. This

allows a range of standard refence generators to be used such as the TL1431, with an adjustable 2.5-V bandgap

reference. Note that an output voltage range of 0 V to 10 V requires a nominal 15 V

± 5% power supply voltage.

DAC section

The TLC7225 contains four, identical, 8-bit voltage-mode DACs. Each converter has a separate reference input.

The output voltages from the converters have the same polarity as the reference voltages, thus allowing single

supply operation.

The simplified circuit diagram for channel A is shown in Figure 4. Note that AGND (terminal 6) is common to

all four DACs.

OUTA

REFA

AGND

DB0

DB5

DB6

DB7

Shown For All 1s On DAC

Figure 4. DAC Simplified-Circuit Diagram

The input impedance at any of the reference inputs is code dependent and can vary from 1.4 k

Ω minimum to

an open circuit. The lowest input impedance at any reference input occurs when that DAC is loaded with the

digital code 01010101. Therefore, it is important that the reference source presents a low output impedance

under changing load conditions. The nodal capacitance at the reference terminals is also code dependent and

typically varies from 60 pF to 300 pF.

Each OUTx terminal can be considered as a digitally programmable voltage source with an output voltage of:

VOUTx = Dx × VREFx

where Dx is the fractional representation of the digital input code and can vary from 0 to 255/256.

The output impedance is that of the output buffer amplifier.

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