ICL7134 Datasheet, PDF (10/16 Pages) Intersil Corporation – 14-Bit Multiplying Microprocessor-Compatible D/A Converter

ICL7134
Digital Section
effective input offset less than 25µV).
Two levels of input buffer registers allow loading of data from
an 8-bit or 16-bit data bus. The A₀ and A₁, pins select one of
four operations: 1) load the LS-buffer register with the data
at inputs D₀ to D₇; 2) load the MS-buffer register with the
data at inputs D₈ to D₁₃; 3) load the DAC register with the
contents of the MS and LS-buffer registers and 4) load the
DAC register directly from the data input pins (See Table 1).
The CS and WR pins must be low to allow data transfers to
occur. When direct loading is selected (CS, WR, A₀ and A₁
low) the registers are transparent, and the data input pins
control the DAC output directly. The other modes of opera-
tion allow double buffered loading of the DAC from an 8-bit
bus.
These input data pins are also used to program the PROM
under control of the PROG pin. This is done in manufactur-
ing, and for normal operation the PROG pin should be tied to
V+ (+5V).
TABLE 1. DATA LOADING CONTROLS
FIGURE 7. GROUND CONNECTIONS
CONTROL I/P
A₀ A₁ CS WR
ICL7134 OPERATION
X X X 1 No Operation, Device Not Selected.
XX1X
0 0 0 0 Load All Registers from Data Bus.
0 1 0 0 Load LS Register from Data Bus.
1 0 0 0 Load MS Register from Data Bus.
1 1 0 0 Load DAC Register from MS and LS
Register.
NOTE: Data is latched on LO-HI transition of either WR or CS.
Applications
GENERAL RECOMMENDATIONS
Grounding
Careful consideration must be given to grounding in any
14-bit accuracy system. The current into the analog ground
point inside the chip varies significantly with the input code
value, and the inevitable resistances between this point and
any external connection pint can lead to significant voltage
drop errors. For this reason, two separate leads are brought
out from this point on the IC, the AGND_F and AGND_S pins.
The varying current should be absorbed through the AGND_F
pin, and the AGND_S pin will then accurately reflect the
voltage on the internal current summing point, as shown in
Figure 7. Thus output signals should be referenced to the
sense pin AGND_S, as shown in the various application
circuits.
Operational Amplifier Selection
To maintain static accuracy, the I_OUT potential must be
exactly equal to the AGND_S potential. Thus output amplifier
selection is critical, in particular low input bias current (less
than 2nA), low offset voltage (less than 25µV) are advisable
if the highest accuracy is needed. Maintaining a low input
offset over a 0V to 10V range also requires that the output
amplifier has a high open loop gain (A_VOL > 400k for
The reference inverting amplifier used in the bipolar mode
circuit must also be selected carefully. If 14-bit accuracy is
desired without adjustment, low input bias current (less than
1nA), low offset voltage (less than 50µV), and high gain
(greater than 400k) are recommended. If a fixed reference
voltage is used, the gain requirement can be relaxed. For
highest accuracy (better than 13-bits), and additional
op-amp may be needed to correct for IR drop on the Analog
GROUND line (op-amp A₂ in Figure 9). This op-amp should
be selected for low bias current (less than 2nA) and low
offset voltage (less than 50µV).
The op-amp requirements can be readily met by use of an
ICL7650 chopper stabilized device. For faster setting time,
an HA26XX can be used with an ICL7650 providing
automatic offset null (see A053 applications note for details)
The output amplifier’s non-inverting input should be tied
directly to AGND_S. A bias current compensation resistor is of
limited use since the output impedance at the summing node
depends on the code being converted in an unpredictable
way. If gain adjustment is required, low tempco (approxi-
mately 50ppm/^oC) resistors or trim-pots should be selected.
Power Supplies
The V+ (pin 25) power supply should have a low noise level,
and no transients exceeding 7 volts. Note that the absolute
maximum for digital input voltage is V+ +0.3V, therefore V+
must be applied before digital inputs are allowed to go high.
Unused digital inputs must be connected to GND or V+ for
proper operation.
Unipolar Binary Operation (ICL7134U)
The circuit configuration for unipolar mode operation
(ICL7134U) is shown in Figure 8. With positive and negative
V_REF values the circuit is capable of two-quadrant
multiplication. The “digital input code/analog output value”
table for unipolar mode is given in Table 2. The Schottky
diode (HP5082-2811 or equivalent) protects I_OUT from
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