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AD7545
August 1997
12-Bit, Buffered, Multiplying CMOS DAC
Description
The AD7545 is a low cost monolithic 12-bit, CMOS multiplying DAC with on-board data latches. Data is loaded in a single 12-bit wide word which allows interfacing directly to most 12-bit and 16-bit bus systems. Loading of the input latches is under the control of the CS and WR inputs. A logic low on these control inputs makes the input latches transparent allowing direct unbuffered operation of the DAC.
Features
* 12-Bit Resolution * Low Gain T.C. 2ppm/oC (Typ) * Fast TTL/CMOS Compatible Data Latches * Single +5V to +15V Supply * Low Power * Low Cost * /883 Processed Versions Available
Ordering Information
PART NUMBER AD7545JN AD7545KN AD7545AN AD7545BN TEMP. RANGE (oC) 0 to 70 0 to 70 -40 to 85 -40 to 85 PACKAGE 20 Ld PDIP 20 Ld PDIP 20 Ld PDIP 20 Ld PDIP PKG. NO. E20.3 E20.3 E20.3 E20.3
Pinout
AD7545 (PDIP) TOP VIEW
Functional Diagram
RFB 20 AD7545 R OUT 1 AGND DGND 1 2 3 4 5 6 7 8 9 20 RFB 19 VREF 18 VDD 17 WR 16 CS 15 DB0 (LSB) 14 DB1 13 DB2 12 DB3 11 DB4 DB11 - DB0 (PINS 4 - 15) CS 16 12 WR 17 INPUT DATA LATCHES 3 DGND 12 18 VDD VREF 19 12-BIT MULTIPLYING DAC 1 2 OUT1 AGND
DB11 (MSB) DB10 DB9 DB8 DB7 DB6
DB5 10
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. http://www.intersil.com or 407-727-9207 | Copyright (c) Intersil Corporation 1999
File Number
3108.1
10-10
AD7545
Absolute Maximum Ratings
Supply Voltage (VDD to DGND) . . . . . . . . . . . . . . . . . . . -0.3V, +17V Digital Input Voltage to DGND . . . . . . . . . . . . . . . .-0.3V, VDD +0.3V VRFB , VREF to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25V VPIN1 to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . .-0.3V, VDD +0.3V AGND to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . .-0.3V, VDD +0.3V
Thermal Information
Thermal Resistance (Typical, Note 1) JA (oC/W) PDIP Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Maximum Junction Temperature (PDIP Package) . . . . . . . . . 150oC Maximum Storage Temperature Range . . . . . . . . . .-65oC to 150oC Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300oC
Operating Conditions
Temperature Ranges Commercial (J, K, Grades) . . . . . . . . . . . . . . . . . . . . .0oC to 70oC Industrial (A, B, Grades) . . . . . . . . . . . . . . . . . . . . . -40oC to 85oC Extended (S Grades) . . . . . . . . . . . . . . . . . . . . . . -55oC to 125oC
CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTE: 1. JA is measured with the component mounted on an evaluation PC board in free air.
Electrical Specifications
PARAMETER STATIC PERFORMANCE Resolution Relative Accuracy J, A, S K, B Differential Nonlinearity
TA = See Note 2, VREF = +10V, VOUT1 = 0V, AGND = DGND, Unless Otherwise Specified VDD = +5V TEST CONDITIONS MIN TYP MAX MIN VDD = +15V TYP MAX UNITS
12 2 1 4 1 20 10
12 2 1 4 1 25 15
Bits LSB LSB LSB LSB LSB LSB
J, A, S 10-Bit Monotonic TMIN to TMAX K, B 12-Bit Monotonic TMIN to TMAX J, A, S DAC Register Loaded with 1111 1111 1111 K, B Gain Error is Adjustable Using the Circuits of Figures 4 and 5 (Note 3) Typical Value is 2ppm/oC for VDD = +5V (Note 4) VDD = 5% J, K A, B S DB0 - DB11 = 0V; WR, CS = 0V (Note 2)
Gain Error (Using Internal RFB)
Gain Temperature Coefficient Gain/Temperature DC Supply Rejection Gain/VDD Output Leakage Current at OUT1
0.015 -
-
5 0.03 50 50 200
0.01 -
-
10 0.02 50 50 200
ppm/oC % nA nA nA s
DYNAMIC CHARACTERISTICS Current Setting Time To 1/2 LSB, OUT1 LOAD = 100, DAC Output Measured from Falling Edge of WR, CS = 0V (Note 4) 2 2
Propagation Delay from Digital Input OUT1 LOAD = 100, Change to 90% of Final Analog CEXT = 13pF (Notes 4 and 5) Output Digital to Analog Glitch Impulse AC Feedthrough at OUT1 ANALOG OUTPUTS Output Capacitance COUT1 COUT1 DB0 - DB11 = 0V, WR, CS = 0V (Note 4) DB0 - DB11 = VDD , WR, CS = 0V (Note 4) VREF = AGND VREF = 10V, 10kHz Sinewave (Note 6)
-
-
300
-
-
250
ns
-
400 5
-
-
250 5
-
nV/s mVP-P
-
-
70 200
-
-
70 200
pF pF
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AD7545
Electrical Specifications
PARAMETER REFERENCE INPUT Input Resistance (Pin 19 to GND) Input Resistance TC = -300ppm/oC (Typ) Typical Input Resistance = 11k DIGITAL INPUTS Input High Voltage, VIH Input Low Voltage, VIL Input Current, IIN Input Capacitance DB0 - DB11 WR, CS VIN = 0 or VDD (Note 7) VIN = 0 (Note 4) VIN = 0 (Note 4) 2.4 1 0.8 10 7 20 1 13.5 1.5 10 7 20 V V A (Max) pF pF 7 25 7 25 k k TA = See Note 2, VREF = +10V, VOUT1 = 0V, AGND = DGND, Unless Otherwise Specified (Continued) VDD = +5V TEST CONDITIONS MIN TYP MAX MIN VDD = +15V TYP MAX UNITS
SWITCHING CHARACTERISTICS (Note 4) Chip Select to Write Setup Time, tCS See Figure 1 Chip Select to Write Hold Time, tCH See Figure 1 Write Pulse Width, tWR Data Setup Time, tDS Data Hold Time, tDH IDD tCS tWR , tCH 0, See Figure 1 See Figure 1 See Figure 1 380 0 400 210 10 200 175 100 200 0 240 120 10 120 100 60 ns ns ns ns ns
POWER SUPPLY CHARACTERISTICS All Digital Inputs VIL or VIH All Digital Inputs 0V or VDD All Digital Inputs 0V or VDD NOTES: 2. Temperature Ranges as follows: J, K versions: 0oC to 70oC A, B versions: -20oC to 85oC S version: -55oC to 125oC oC for TYP Specifications. MIN and MAX are measured over the specified operating range. TA = 25 3. This includes the effect of 5ppm maximum gain TC. 4. Parameter not tested. Parameter guaranteed by design, simulation, or characterization. 5. DB0 - DB11 = 0V to VDD or VDD to 0V in plastic and sidebraze package. 6. Feedthrough can be further reduced by connecting the metal lid on the ceramic package to DGND. 7. Logic inputs are MOS gates. Typical input current (25oC) is less than 1nA. 8. Typical values are not guaranteed but reflect mean performance specification. Specifications subject to change without notice. 100 10 2 500 100 10 2 500 mA A A
Timing Diagrams
tCH CHIP SELECT tCS VDD 0 WRITE tWR tDH tDS DATA IN (DB0 - DB11) DATA VALID VDD 0 VDD 0 tDS DATA IN (DB0 - DB11) DATA VALID WRITE tWR tDH CHIP SELECT tCS tCH VDD 0 VDD 0 VDD 0
FIGURE 1A. TYPICAL WRITE CYCLE
FIGURE 1B. PREFERRED WRITE CYCLE
FIGURE 1. WRITE CYCLE TIMING DIAGRAM
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AD7545
MODE SELECTION WRITE MODE: CS and WR low, DAC responds to data bus (DB0 - DB11) inputs HOLD MODE: Either CS or WR high, data bus (DB0 - DB11) is locked out; DAC holds last data present when WR or CS assumed high state.
equal to the value "R"). Since RIN at the VREF pin is constant, the reference terminal can be driven by a reference voltage or a reference current, AC or DC, of positive or negative polarity. (If a current source is used, a low temperature coefficient external RFB is recommended to define scale factor).
Circuit Information - Digital Section
Figure 4 shows the digital structure for one bit. The digital signals CONTROL and CONTROL are generated from CS and WR.
TO AGND SWITCH
NOTES: 9. VDD = +5V; tr = tf = 20ns 10. VDD = +15V; tr = tf = 40ns 11. All input signal rise and fall times measured from 10% to 90% of VDD . 12. Timing measurement reference level is (VIH + VIL)/2. 13. Since input data latches are transparent for CS and WR both low, it is preferred to have data valid before CS and WR both go low. This prevents undesirable changes at the analog output while the data inputs settle.
TO OUT1 SWITCH INPUTS BUFFERS
CONTROL
CONTROL
Circuit Information - D/A Converter Section
Figure 2 shows a simplified circuit of the D/A converter section of the AD7545. Note that the ladder termination resistor is connected to AGND. R is typically 11k. The binary weighted currents are switched between the OUT1 bus line and AGND by N-Channel switches, thus maintaining a constant current in each ladder leg independent of the switch state. One of the current switches is shown in Figure 3.
VREF R R R R
FIGURE 4. DIGITAL INPUT STRUCTURE
The input buffers are simple CMOS inverters designed such that when the AD7545 is operated with VDD = 5V, the buffers convert TTL input levels (2.4V and 0.8V) into CMOS logic levels. When VIN is in the region of 2.0V to 3.5V the input buffers operate in their linear region and draw current from the power supply. To minimize power supply currents it is recommended that the digital input voltages be as close to the supply rails (VDD and DGND) as is practically possible. The AD7545 may be operated with any supply voltage in the range 5V VDD 15V. With VDD = +15V the input logic levels are CMOS compatible only, i.e., 1.5V and 13.5V.
2R
2R
2R
2R
2R
2R
RFB OUT1 AGND DB11 (MSB) DB10 DB9 DB1 DB0 (LSB)
Application
Output Offset CMOS current-steering D/A converters exhibit a code dependent output resistance which in turn causes a code dependent amplifier noise gain. The effect is a code dependent differential nonlinearity term at the amplifier output which depends on VOS where VOS is the amplifier input offset voltage. To maintain monotonic operation it is recommended that VOS be no greater than (25 x 10-6) (VREF) over the temperature range of operation. General Ground Management AC or transient voltages between AGND and DGND can cause noise injection into the analog output. The simplest method of ensuring that voltages at AGND and DGND are equal is to tie AGND and DGND together at the AD7545. In more complex systems where the AGND and DGND connection is on the backplane, it is recommended that two diodes be connected in inverse parallel between the AD7545 AGND and DGND pins (1N914 or equivalent). Digital Glitches When WR and CS are both low the latched are transparent and the D/A converter inputs follow the data inputs. In some
FIGURE 2. SIMPLIFIED D/A CIRCUIT OF AD7545
TO LADDER
FROM INTERFACE LOGIC
AGND
OUT1
FIGURE 3. N-CHANNEL CURRENT STEERING SWITCH
The capacitance at the OUT1 bus line, COUT1, is code dependent and varies from 70pF (all switches to AGND) to 200pF (all switches to OUT1). The input resistance at VREF (Figure 2) is always equal to RLDR (RLDR is the R/2R ladder characteristic resistance and is
10-13
AD7545
bus systems, data on the data bus is not always valid for the whole period during which WR is low and as a result invalid data can briefly occur at the D/A converter inputs during a write cycle. Such invalid data can cause unwanted glitches at the output of the D/A converter. The solution to this problem, if it occurs, is to retime the write pulse (WR) so that it only occurs when data is valid. Another cause of digital glitches is capacitive coupling from the digital lines to the OUT1 and AGND terminals. This should be minimized by isolating the analog pins of the AD7545 (pins 1, 2, 19, 20) from the digital pins by a ground track run between pins 2 and 3 and between pins 18 and 19 of the AD7545. Note how the analog pins are at one end of the package and separated from the digital pins by VDD and DGND to aid isolation at the board level. On-chip capacitive coupling can also give rise to crosstalk from the digital to analog sections of the AD7545, particularly in circuits with high currents and fast rise and fall times. This type of crosstalk is minimized by using VDD = +5V. However, great care should be taken to ensure that the +5V used to power the AD7545 is free from digitally induces noise. Temperature Coefficients The gain temperature coefficient of the AD7545 has a maximum value of 5ppm/oC and a typical value of 2ppm/oC. This corresponds to worst case gain shifts of 2 LSBs and 0.8 LSBs respectively over a 100oC temperature range. When trim resistors R1 and R2 are used to adjust full scale range, the temperature coefficient of R1 and R2 should also be taken into account. The choice of the operational amplifiers in Figure 4 and Figure 5 depends on the application and the trade off between required precision and speed. Below is a list of operational amplifiers which are good candidates for many applications. The main selection criteria for these operational amplifiers is to have low VOS , low VOS drift, low bias current and low settling time. These amplifiers need to maintain the low nonlinearity and monotonic operation of the D/A while providing enough speed for maximum converter performance. Operational Amplifiers HA5127 HA5137 HA5147 HA5170 Ultra Low Noise, Precision Ultra Low Noise, Precision, Wide Band Ultra Low Noise, Precision, High Slew Rate Precision, JFET Input
TABLE 1. RECOMMENDED TRIM RESISTOR VALUES vs GRADES FOR VDD = +5V TRIM RESISTOR R1 R2 J, A, S 500 150 K, B 200 68
TABLE 2. UNIPOLAR BINARY CODE TABLE FOR CIRCUIT OF FIGURE 4 BINARY NUMBER IN DAC REGISTER 1111 1000 0000 0000 1111 0000 0000 0000 1111 0000 0001 0000
Basic Applications
Figures 5 and 6 show simple unipolar and bipolar circuits using the AD7545. Resistor R1 is used to trim for full scale. Capacitor C1 provides phase compensation and helps prevent overshoot and ringing when using high speed op amps. Note that the circuits of Figures 5 and 6 have constant input impedance at the VREF terminal. The circuit of Figure 4 can either be used as a fixed reference D/A converter so that it provides an analog output voltage in the range 0V to -VIN (note the inversion introduced by the op amp) or VIN can be an AC signal in which case the circuit behaves as an attenuator (2-Quadrant Multiplier). VIN can be any voltage in the range -20V VIN +20V (provided the op amp can handle such voltages) since VREF is permitted to exceed VDD . Table 2 shows the code relationship for the circuit of Figure 4. Figure 5 and Table 3 illustrate the recommended circuit and code relationship for bipolar operation. The D/A function itself uses offset binary code and inverter U1 on the MSB line converts 2's complement input code to offset binary code. If appropriate, inversion of the MSB may be done in software using an exclusive -OR instruction and the inverter omitted. R3, R4 and R5 must be selected to match within 0.01% and they should be the same type of resistor (preferably wire-wound or metal foil), so that their temperature coefficients match. Mismatch of R3 value to R4 causes both offset and full scale error. Mismatch of R5 to R4 and R3 causes full scale error.
ANALOG OUTPUT 4095 - V IN ------------ 4096 2048 1 - V IN ------------ = - -- V IN 2 4096
1 - V IN ------------ 4096 0V
TABLE 3. 2'S COMPLEMENT CODE TABLE FOR CIRCUIT OF FIGURE 5 DATA INPUT 0111 0000 0000 1111 1000 1111 0000 0000 1111 0000 1111 0001 0000 1111 0000 ANALOG OUTPUT 2047 +V IN * ------------ 2048 1 +V IN * ------------ 2048 0V 1 - V IN * ------------ 2048 2048 - V IN * ------------ 2048
10-14
AD7545
VDD
R2 (NOTE)
18 VIN 19 VREF R1* WR 17 16 CS VDD
20 RFB OUT 1 AGND DGND 3 2 1
C1 33pF
+
VOUT
AD7545
ANALOG COMMON DB11 - DB0 (PINS 4 - 15)
NOTE: REFER TO TABLE 1
FIGURE 5. UNIPOLAR BINARY OPERATION
VDD
R2 (NOTE)
R4 20K C1 33pF
18 VIN 19 VREF R1 (NOTE) WR 17 16 CS U1 (SEE TEXT) DB11 4 VDD
20 RFB OUT 1 AGND 2 DB10 - DB0 3 DGND 11 12 1
R3 10K A1 R6 5K
R5 20K
AD7545
A2 +
VOUT
ANALOG COMMON NOTE: FOR VALUES OF R1 AND R2 SEE TABLE 1
DATA INPUT
FIGURE 6. BIPOLAR OPERATION (2'S COMPLEMENT CODE)
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AD7545 Die Characteristics
DIE DIMENSIONS: 121 mils x 123 mils (3073micrms x 3124micrms) METALLIZATION: Type: Pure Aluminum Thickness: 10 1kA PASSIVATION: Type: PSG/Nitride PSG: 7 1.4kA Nitride: 8 1.2kA PROCESS: CMOS Metal Gate
Metallization Mask Layout
AD7545
PIN 4 DB11 (MSB)
PIN 7 DB8
PIN 6 DB9
PIN 5 DB10
PIN 3 DGND
PIN 2 AGND
PIN 1 OUT1 PIN 8 DB7
PIN 9 DB6
PIN 10 DB5
PIN 11 DB4
PIN 20 RFEEDBACK PIN 19 VREF
PIN 12 DB3
PIN 13 DB2
PIN 18 VDD
PIN 14 DB1
PIN 15 DB0 (LSB)
PIN 16 CS
PIN 17 WR
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Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries 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 Intersil or its subsidiaries.
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