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PDF DAC7545 Data sheet ( Hoja de datos )

Número de pieza DAC7545
Descripción CMOS 12-Bit Multiplying DIGITAL-TO-ANALOG CONVERTER Microprocessor Compatible
Fabricantes Burr-Brown Corporation 
Logotipo Burr-Brown Corporation Logotipo



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DAC7545
DAC7545
DAC7545
CMOS 12-Bit Multiplying
DIGITAL-TO-ANALOG CONVERTER
Microprocessor Compatible
FEATURES
q FOUR-QUADRANT MULTIPLICATION
q LOW GAIN TC: 2ppm/°C typ
q MONOTONICITY GUARANTEED OVER
TEMPERATURE
q SINGLE 5V TO 15V SUPPLY
q TTL/CMOS LOGIC COMPATIBLE
q LOW OUTPUT LEAKAGE: 10nA max
q LOW OUTPUT CAPACITANCE: 70pF max
q DIRECT REPLACEMENT FOR AD7545,
PM-7545
DESCRIPTION
The DAC7545 is a low-cost CMOS, 12-bit four-
quadrant multiplying, digital-to-analog converter with
input data latches. The input data is loaded into the
DAC as a 12-bit data word. The data flows through to
the DAC when both the chip select (CS) and the write
(WR) pins are at a logic low.
Laser-trimmed thin-film resistors and excellent CMOS
voltage switches provide true 12-bit integral and dif-
ferential linearity. The device operates on a single
+5V to +15V supply and is available in 20-pin plastic
DIP or 20-lead plastic SOIC packages. Devices are
specified over the commercial.
The DAC7545 is well suited for battery or other low
power applications because the power dissipation is
less than 0.5mW when used with CMOS logic inputs
and VDD = +5V.
RFB
20
VREF 19
WR 17
CS 16
12-Bit
Multiplying DAC
12
Input
Data Latches
12
DB11-DB0
(Pins 4-15)
1 OUT 1
2 AGND
18 VDD
3 DGND
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
©1987 Burr-Brown Corporation
PDS1-747F
DPrAintCed 7in 5U.4S.A5. August, 1997

1 page




DAC7545 pdf
Propagation Delay
The delay of the internal circuitry is measured as the time
from a digital code change to the point at which the
output reaches 90% of final value.
current than normal. Minimizing this transition time through
the linear region and insuring that the digital inputs are
operated as close to the rails as possible will minimize the
supply drain current.
Digital-to-Analog Glitch Impulse
The area of the glitch energy measured in nanovolt-seconds.
Key contributions to glitch energy are internal circuitry
timing differences and charge injected from digital
logic. The measurement is performed with VREF = GND and
an OPA600 as the output op amp and G1 (phase
compensation) = 0pF.
Monotonicity
Monotonicity assures that the analog output will increase
or stay the same for increasing digital input codes. The
DAC7545 is guaranteed monotonic to 12 bits, except the
J grade is specified to be 10-bit monotonic.
Power Supply Rejection
Power supply rejection is the measure of the sensitivity of
the output (full scale) to a change in the power supply
voltage.
CIRCUIT DESCRIPTION
Figure 1 shows a simplified schematic of the digital-to-
analog converter portion of the DAC7545. The current from
the VREF pin is switched from OUT 1 to AGND by the
FET switch. This circuit architecture keeps the resistance at
the reference pin constant and equal to RLDR, so the reference
could be provided by either a voltage or current, AC or DC,
positive or negative polarity, and have a voltage range up to
±20V even with VDD = 5V. The RLDR is equal to “R” and is
typically 11k.
VREF
R
R
R
R
2R 2R 2R
2R 2R RFB
OUT 1
DB11
(MSB)
DB10
DB9
DB0
(LSB)
AGND
FIGURE 1. Simplified DAC Circuit of the DAC7545.
The output capacitance of the DAC7545 is code dependent
and varies from a minimum value (70pF) at code 000H to a
maximum (200pF) at code FFFH.
The input buffers are CMOS inverters, designed so that
when the DAC7545 is operated from a 5V supply (VDD), the
logic threshold is TTL-compatible. Being simple CMOS
inverters, there is a range of operation where the inverters
operate in the linear region and thus draw more supply
APPLICATIONS
UNIPOLAR OPERATION
Figure 2 shows the DAC7545 connected for unipolar opera-
tion. The high-grade DAC7545 is specified for a 1LSB gain
error, so gain adjust is typically not needed. However, the
resistors shown are for adjusting full-scale errors. The value
of R1 should be minimized to reduce the effects of mis-
matching temperature coefficients between the internal and
external resistors. A range of adjustment of 1.5 times the
desired range will be adequate. For example, for a
DAC7545JP, the gain error is specified to be ±25LSB. A
range of adjustment of ±37LSB will be adequate. The
equation below results in a value of 458for the potentiom-
eter (use 500).
R1 =
RLADDER
4096
(3 x Gain Error)
The addition of R1 will cause a negative gain error. To
compensate for this error, R2 must be added. The value of R2
should be one-third the value of R1.
The capacitor across the feedback resistor is used to com-
pensate for the phase shift due to stray capacitances of the
circuit board, the DAC output capacitance, and op amp input
capacitance. Eliminating this capacitor will result in exces-
sive ringing and an increase in glitch energy. This capacitor
should be as small as possible to minimize settling time.
The circuit of Figure 2 may be used with input voltages up
to ±20V as long as the output amplifier is biased to handle
the excursions. Table I represents the analog output for four
codes into the DAC for Figure 2.
+5V R2
C1
VIN
VDD RFB
33pF
VREF
OUT 1
R1
DAC7545
AGND
DGND
OPA604
VOUT
DB0-DB11
FIGURE 2. Unipolar Binary Operation.
BINARY CODE
MSB
LSB
1111 1111 1111
1000 0000 0000
0000 0000 0001
0000 0000 0000
TABLE I. Unipolar Codes.
ANALOG OUTPUT
–VIN (4095/4096)
–VIN (2048/4096) = –1/2VIN
–VIN (1/4096)
0V
5 DAC7545

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