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FEATURES Complete 8-Bit DAC Voltage Output--0 V to 2.56 V Internal Precision Band-Gap Reference Single-Supply Operation: +5 V ( 10%) Full Microprocessor Interface Fast: 1 s Voltage Settling to 1/2 LSB Low Power: 75 mW No User Trims Required Guaranteed Monotonic Over Temperature All Errors Specified TMIN to TMAX Small 16-Pin DIP or 20-Pin PLCC Package Low Cost
DACPORT, Low-Cost Complete P-Compatible 8-Bit DAC AD557
FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD557 DACPORT(R) is a complete voltage-output 8-bit digital-to-analog converter, including output amplifier, full microprocessor interface and precision voltage reference on a single monolithic chip. No external components or trims are required to interface, with full accuracy, an 8-bit data bus to an analog system. The low cost and versatility of the AD557 DACPORT are the result of continued development in monolithic bipolar technologies. The complete microprocessor interface and control logic is implemented with integrated injection logic (I2L), an extremely dense and low-power logic structure that is process-compatible with linear bipolar fabrication. The internal precision voltage reference is the patented low-voltage band-gap circuit which permits full-accuracy performance on a single +5 V power supply. Thin-film silicon-chromium resistors provide the stability required for guaranteed monotonic operation over the entire operating temperature range, while laser-wafer trimming of these thin-film resistors permits absolute calibration at the factory to within 2.5 LSB; thus, no user-trims for gain or offset are required. A new circuit design provides voltage settling to 1/2 LSB for a full-scale step in 800 ns. The AD557 is available in two package configurations. The AD557JN is packaged in a 16-pin plastic, 0.3"-wide DIP. For surface mount applications, the AD557JP is packaged in a 20-pin JEDEC standard PLCC. Both versions are specified over the operating temperature range of 0C to +70C.
DACPORT is a registered trademark of Analog Devices, Inc. Covered by U.S. Patent Nos. 3,887,863; 3,685,045; 4,323,795; other patents pending.
1. The 8-bit I2L input register and fully microprocessorcompatible control logic allow the AD557 to be directly connected to 8- or 16-bit data buses and operated with standard control signals. The latch may be disabled for direct DAC interfacing. 2. The laser-trimmed on-chip SiCr thin-film resistors are calibrated for absolute accuracy and linearity at the factory. Therefore, no user trims are necessary for full rated accuracy over the operating temperature range. 3. The inclusion of a precision low-voltage band-gap reference eliminates the need to specify and apply a separate reference source. 4. The AD557 is designed and specified to operate from a single +4.5 V to +5.5 V power supply. 5. Low digital input currents, 100 A max, minimize bus loading. Input thresholds are TTL/low voltage CMOS compatible. 6. The single-chip, low power I2L design of the AD557 is inherently more reliable than hybrid multichip or conventional single-chip bipolar designs.
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Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
AD557-SPECIFICATIONS (@ T = +25 C, V
A
CC
= +5 V unless otherwise noted)
PIN CONFIGURATIONS DIP
LSB BIT 8 1 BIT 7 2 16 VOUT 15 VOUT SENSE A
Model RESOLUTION RELATIVE ACCURACY 0 to + 70C OUTPUT Ranges Current Source Sink OUTPUT SETTLING TIME 3 FULL-SCALE ACCURACY 4 @ +25C TMIN to TMAX ZERO ERROR @ +25C TMIN to TMAX MONOTONICITY 5 TMIN to TMAX DIGITAL INPUTS TMIN to TMAX Input Current Data Inputs, Voltage Bit On--Logic "1" Bit On--Logic "0" Control Inputs, Voltage On--Logic "1" On--Logic "0" Input Capacitance TIMING6 tW Strobe Pulse Width TMIN to TMAX tDH Data Hold Time TMIN to TMAX tDS Data Setup Time TMIN to TMAX POWER SUPPLY Operating Voltage Range (V CC) 2.56 Volt Range Current (ICC) Rejection Ratio POWER DISSIPATION, V CC = 5 V OPERATING TEMPERATURE RANGE
Min
Typ
Max 8
Units Bits LSB V mA
1/2
1
0 to + 2.56 +5 Internal Passive Pull-Down to Ground 2 0.8 1.5 2.5 1.5 2.5 4.0 1 3 Guaranteed
s LSB LSB LSB LSB
BIT 6 3 BIT 5 4
AD557
14 VOUT SENSE B 13 GND
TOP VIEW BIT 4 5 (Not to Scale) 12 GND BIT 3 6 BIT 2 7 11 +VCC 10 CS 9 CE
MSB BIT 1 8
100 2.0 0 2.0 0 4 225 300 10 10 225 300
A V V V V pF ns ns ns ns ns ns
BIT 6 4 BIT 5 5 NC 6 BIT 4 7 BIT 3 8 9
PLCC
VOUT SENSE A
18 VOUT SENSE B 17 GND 16 NC 15 GND 14 +VCC 10 11 12 13
BIT 8 (LSB)
0.8
BIT 7
3
2
NC
1
0.8
20 19
PIN 1 IDENTIFIER
AD557
TOP VIEW (Not to Scale)
(MSB) BIT 1
BIT 2
NC
15 75 0
125 +70
mW C
NC = NO CONNECT
NOTES 1 Relative Accuracy is defined as the deviation of the code transition points from the ideal transfer point on a straight line from the zero the the full scale of the device. 2 Passive pull-down resistance is 2 k. 3 Settling time is specified for a positive-going full-scale step to 1/2 LSB. Negativegoing steps to zero are slower, but can be improved with an external pull-down. 4 The full-scale output voltage is 2.55 V and is guaranteed with a +5 V supply. 5 A monotonic converter has a maximum differential lineraity error of 1 LSB. 6 See Figure 7. Specifications subject to change without notice.
ORDERING GUIDE
Model AD557JN AD557JP
Temperature Range 0C to +70C 0C to +70C
CE
CS
+4.5
+5.5 25 0.03
V mA %/%
VOUT
Package Option* N-16 P-20A
ABSOLUTE MAXIMUM RATINGS *
*N = Plastic DIP; P = Plastic Leaded Chip Carrier.
VCC to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V to +18 V Digital Inputs (Pins 1-10) . . . . . . . . . . . . . . . . . . 0 V to +7.0 V VOUT . . . . . . . . . . . . . . . . . . . . . . . Indefinite Short to Ground Momentary Short to VCC Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 mW Storage Temperature Range N/P (Plastic) Packages . . . . . . . . . . . . . . . . -25C to +100C Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . . 300C Thermal Resistance Junction to Ambient/Junction to Case N/P (Plastic) Packages . . . . . . . . . . . . . . . . . .140/55C/W
*Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
CIRCUIT DESCRIPTION
The AD557 consists of four major functional blocks fabricated on a single monolithic chip (see Figure 1). The main D/A converter section uses eight equally weighted laser-trimmed current sources switched into a silicon-chromium thin-film R/2R resistor ladder network to give a direct but unbuffered 0 mV to 400 mV output range. The transistors that form the DAC switches are PNPs; this allows direct positive-voltage logic interface and a zero-based output range.
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REV. A
AD557
and offset; therefore, no provisions have been made for such user trims. If a small increase in scale is required, however, it may be accomplished by slightly altering the effective gain of the output buffer. A resistor in series with VOUT SENSE will increase the output range. Note that decreasing the scale by putting a resistor in series with GND will not work properly due to the code-dependent currents in GND. Adjusting offset by injecting dc at GND is not recommended for the same reason.
Figure 1. Functional Block Diagram
The high-speed output buffer amplifier is operated in the noninverting mode with gain determined by the userconnections at the output range select pin. The gain-setting application resistors are thin film laser trimmed to match and track the DAC resistors and to assure precise initial calibration of the output range, 0 V to 2.56 V. The amplifier output stage is an NPN transistor with passive pull-down for zero-based output capability with a single power supply. The internal precision voltage reference is of the patented band-gap type. This design produces a reference voltage of 1.2 V and thus, unlike 6.3 V temperature-compensated Zeners, may be operated from a single, low-voltage logic power supply. The microprocessor interface logic consists of an 8-bit data latch and control circuitry. Low power, small geometry and high speed are advantages of the I2L design as applied to this section. I2L is bipolar process compatible so that the performance of the analog sections need not be compromised to provide on-chip logic capabilities. The control logic allows the latches to be operated from a decoded microprocessor address and write signal. If the application does not involve a P or data bus, wiring CS and CE to ground renders the latches "transparent" for direct DAC access. Binary 0000 0000 0000 0001 0000 0010 0000 1111 0001 0000 0111 1111 1000 0000 1100 0000 1111 1111 Digital Input Code Hexadecimal 00 01 02 0F 10 7F 80 C0 FF Decimal 0 1 2 15 16 127 128 192 255 Output Voltage 0 0.010 V 0.020 V 0.150 V 0.160 V 1.270 V 1.280 V 1.920 V 2.55 V
Figure 2. 0 V to 2.56 V Output Range
BIPOLAR -1.28 V TO +1.28 V OUTPUT RANGE
The AD557 was designed for operation from a single power supply and is thus capable of providing only a unipolar 0 V to +2.56 V output range. If a negative supply is available, bipolar output ranges may be achieved by suitable output offsetting and scaling. Figure 3 shows how a 1.28 V output range may be achieved when a -5 V power supply is available. The offset is provided by the AD589 precision 1.2 V reference which will operate from a +5 V supply. The AD711 output amplifier can provide the necessary 1.28 V output swing from 5 V supplies. Coding is complementary offset binary.
Figure 3. Bipolar Operation of AD557 from 5 V Supplies
Applications
GROUNDING AND BYPASSING
CONNECTING THE AD557 The AD557 has been configured for low cost and ease of application. All reference, output amplifier and logic connections are made internally. In addition, all calibration trims are performed at the factory assuring specified accuracy without user trims. The only connection decision to be made by the user is whether the output range desired is unipolar or bipolar. Clean circuit board layout is facilitated by isolating all digital bit inputs on one side of the package; analog outputs are on the opposite side.
UNIPOLAR 0 V TO +2.56 V OUTPUT RANGE
All precision converter products require careful application of good grounding practices to maintain full rated performance. Because the AD557 is intended for application in microcomputer systems where digital noise is prevalent, special care must be taken to assure that its inherent precision is realized. The AD557 has two ground (common) pins; this minimizes ground drops and noise in the analog signal path. Figure 4 shows how the ground connections should be made. It is often advisable to maintain separate analog and digital grounds throughout a complete system, tying them common in one place only. If the common tie-point is remote and accidental disconnection of that one common tie-point occurs due to card removal with power on, a large differential voltage between the -3-
Figure 2 shows the configuration for the 0 V to +2.56 V fullscale output range. Because of its precise factory calibration, the AD557 is intended to be operated without user trims for gain REV.A
AD557
two commons could develop. To protect devices that interface to both digital and analog parts of the system, such as the AD557, it is recommended that common ground tie-points should be provided at each such device. If only one system ground can be connected directly to the AD557, it is recommended that analog common be selected.
Table I. AD557 Control Logic Truth Table
Input Data 0 1 0 1 0 1 X X CE 0 0 g g 0 0 1 X CS 0 0 0 0 g g X 1 DAC Data 0 1 0 1 0 1 previous data previous data Latch Condition "transparent" "transparent" latching latching latching latching latched latched
NOTES X = Does not matter g = Logic Threshold at Positive-Going Transition
Figure 4. Recommended Grounding and Bypassing
USING A "FALSE" GROUND
Many applications, such as disk drives, require servo control voltages that swing on either side of a "false" ground. This ground is usually created by dividing the +12 V supply equally and calling the midpoint voltage "ground." Figure 5 shows an easy and inexpensive way to implement this. The AD586 is used to provide a stable 5 V reference from the system's +12 V supply. The op amp shown likewise operates from a single (+12 V) supply available in the system. The resulting output at the VOUT node is 2.5 V around the "false" ground point of 5 V. AD557 input code vs. VOUT is shown in Figure 6.
In a level-triggered latch such as that used in the AD557, there is an interaction between the data setup and hold times and the width of the enable pulse. In an effort to reduce the time required to test all possible combinations in production, the AD557 is tested with TDS = TW = 225 ns at 25C and 300 ns at TMIN and TMAX, with TDH = 10 ns at all temperatures. Failure to comply with these specifications may result in data not being latched properly. Figure 7 shows the timing for the data and control signals, CE and CS are identical in timing as well as in function.
Figure 7. AD557 Timing Figure 5. Level Shifting the AD557 Output Around a "False" Ground
TIMING AND CONTROL OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
P (PLCC) Package
Figure 6. AD557 Input Code vs. Level Shifted Output in a "False" Ground Configuration
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REV. A
PRINTED IN U.S.A.
The AD557 has data input latches that simplify interface to 8and 16-bit data buses. These latches are controlled by Chip Enable (CE) and Chip Select (CS) inputs. CE and CS are internally "NORed" so that the latches transmit input data to the DAC section when both CE and CS are at Logic "0". If the application does not involve a data bus, a "00" condition allows for direct operation of the DAC. When either CE or CS go to Logic "1," the input data is latched into the registers and held until both CE and CS return to "0." (Unused CE or CS inputs should be tied to ground.) The truth table is given in Table I. The logic function is also shown in Figure 6.
N (Plastic) Package
C1109a-5-6/88

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