Datasheet AD584 (Analog Devices) - 6

link to page 6 link to page 6 link to page 6 link to page 6 link to page 6 link to page 6 link to page 6 link to page 6
AD584 Data Sheet THEORY OF OPERATION APPLYING THE AD584
approximately 20 V, even for the large values of R1. Do not With power applied to Pin 8 and Pin 4 and all other pins open, omit R2; choose its value to limit the output to a value that can the AD584 produces a buffered nominal 10.0 V output between be tolerated by the load circuits. If R2 is zero, adjusting R1 to its Pin 1 and Pin 4 (see Figure 3). The stabilized output voltage can lower limit results in a loss of control over the output voltage. be reduced to 7.5 V, 5.0 V, or 2.5 V by connecting the programming When precision voltages are set at levels other than the standard pins as shown in Table 4. outputs, account for the 20% absolute tolerance in the internal resistor ladder.
Table 4.
Alternatively, the output voltage can be raised by loading the
Output
2.5 V tap with R3 alone. The output voltage can be lowered by
Voltage (V) Pin Programming
connecting R4 alone. Either of these resistors can be a fixed 7.5 Join the 2.5 V (Pin 3) and 5.0 V (Pin 2) pins. resistor selected by test or an adjustable resistor. In all cases, the 5.0 Connect the 5.0 V pin (Pin 2) to the output pin (Pin 1). resistors should have a low temperature coefficient to match the 2.5 Connect the 2.5 V pin (Pin 3) to the output pin (Pin 1). AD584 internal resistors, which have a negative temperature The options shown in Table 4 are available without the use of any coefficient less than 60 ppm/°C. If both R3 and R4 are used, additional components. Multiple outputs using only one AD584 these resistors should have matching temperature coefficients. can be provided by buffering each voltage programming pin When only small adjustments or trims are required, the circuit with a unity-gain, noninverting op amp. in Figure 4 offers better resolution over a limited trim range. The
VSUPPLY
circuit can be programmed to 5.0 V, 7.5 V, or 10 V, and it can be
8
adjusted by means of R1 over a range of about ±200 mV. To trim
AD584 VOUT
the 2.5 V output option, R2 (see Figure 4) can be reconnected to
10V
the band gap reference (Pin 6). In this configuration, limit the
1 1.215V 24kΩ
adjustment to ±100 mV to avoid affecting the performance of
R4 5V
the AD584.
2 * 12kΩ V+ 2.5V R1 3 8 VOUT 6kΩ 10.0V V 1 BG R3 6 R2 5.0V 2 6kΩ R2 AD584 2.5V 300kΩ R1 3 10kΩ COMMON 4 VBG 6 * THE 2.5V TAP IS USED INTERNALLY AS A BIAS POINT
004
4 AND SHOULD NOT BE CHANGED BY MORE THAN 100mV
005
IN ANY TRIM CONFIGURATION.
00527-
COMMON
Figure 3. Variable Output Options 00527- Figure 4. Output Trimming The AD584 can also be programmed over a wide range of output
V+
voltages, including voltages greater than 10 V, by the addition
R40 R41 Q7
of one or more external resistors. Figure 3 illustrates the general
STROBE Q20 Q10 Q11 Q8
adjustment procedure, with approximate values given for the
C52 Q12 Q15 R42
internal resistors of the AD584. The AD584 may be modeled
OUT 10V C51 R34
as an op amp with a noninverting feedback connection, driven
Q6 Q14 5V TAP
by a high stability 1.215 V band gap reference (see Figure 5 for
R37 Q5 2.5V TAP
schematic).
Q16 Q13 R35 SUB
When the feedback ratio is adjusted with external resistors, the
C50 R33 R32
output amplifier can be made to multiply the reference voltage
CAP
by almost any convenient amount, making popular outputs of
Q3 Q4
10.24 V, 5.12 V, 2.56 V, or 6.3 V easy to obtain. The most general
R38 Q2 VBG
adjustment (which gives the greatest range and poorest resolution)
Q1 R30
uses R1 and R2 alone (see Figure 3). As R1 is adjusted to its upper 006 limit, the 2.5V pin (Pin 3) is connected to the output, which
R39 R31 R36 V–
00527- reduces to 2.5 V. As R1 is adjusted to its lower limit, the output Figure 5. Schematic Diagram voltage rises to a value limited by R2. For example, if R2 is approximately 6 kΩ, the upper limit of the output range is Rev. C | Page 6 of 12 Document Outline Features General Description Pin Configurations Product Highlights Table of Contents Revision History Specifications Absolute Maximum Ratings ESD Caution Theory of Operation Applying the AD584 Performance over Temperature Output Current Characteristics Dynamic Performance Noise Filtering Using the Strobe Terminal Percision High Current Supply The AD584 as a Current Limiter Negative Reference Voltages from an AD584 10 V Reference with Multiplying CMOS DACs or ADCs Precision DAC Reference Outline Dimensions Ordering Guide