Datasheet ADR512W (Analog Devices) - 8

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ADR512W APPLICATIONS INFORMATION
The ADR512W is a 1.2 V precision shunt voltage reference. It is
OUTPUT VOLTAGE TRIM
designed to operate without an external output capacitor Using a mechanical or digital potentiometer, the output voltage between the positive and negative terminals for stability. An of the ADR512W can be trimmed ±0.5%. The circuit in Figure 12 external capacitor can be used for additional filtering of the illustrates how the output voltage can be trimmed using a 10 k Ω supply. potentiometer. As with all shunt voltage references, an external bias resistor
VCC
(RBIAS) is required between the supply voltage and the ADR512W (see Figure 2). RBIAS sets the current that is required
RBIAS
to pass through the load (IL) and the ADR512W (IQ). The load
VOUT
and the supply voltage can vary, thus R
POT
BIAS is chosen as follows:
ADR512W 50kΩ R1
• R
100kΩ
BIAS must be smal enough to supply the minimum IQ 012 current to the ADR512W even when the supply voltage is 09938- at its minimum and the load current is at its maximum Figure 12. Output Voltage Trim value. •
USING THE ADR512W WITH PRECISION DATA
RBIAS also must be large enough so that IQ does not exceed 10 mA when the supply voltage is at its maximum and the
CONVERTERS
load current is at its minimum. The compact ADR512W package and the device’s low minimum operating current requirement make it ideal for use Given these conditions, RBIAS is determined by the supply in battery powered portable instruments, such as the AD7533 voltage (VS), the load and operating current (IL and IQ) of the CMOS multiplying DAC, that use precision data converters. ADR512W, and the ADR512W’s output voltage. Figure 13 shows the ADR512W serving as an external reference RBIAS = (VS − VOUT)/(IL + IQ) (3) to the AD7533, a CMOS multiplying DAC. Such a DAC
ADJUSTABLE PRECISION VOLTAGE SOURCE
requires a negative voltage input to provide a positive output The ADR512W, combined with a precision low input bias op range. In this application, the ADR512W supplies a −1.2 V amp such as the AD8610, can be used to output a precise reference to the REF input of the AD7533. adjustable voltage. Figure 11 illustrates the implementation of this
0 9
application using the ADR512W.
+ MSB LSB ADR512W VDD 1 – AD7533
The output of the op amp, VOUT, is determined by the gain of the circuit, which is completely dependent on resistors R2 and R1.
1 G R2 N 3
R2
2 1 15
V = 1 + (4) OUT 1 R
–VDD +
An additional capacitor in parallel with R2 can be added to
VOUT = 0V TO 1.2V
filter out high frequency noise. The value of C2 is dependent on
–
013 the value of R2. 09938- Figure 13. The ADR512W as a Reference for a 10-Bit CMOS DAC (AD7533)
VCC PRECISE NEGATIVE VOLTAGE REFERENCE RBIAS 1.2V
The ADR512W is suitable for use in applications where a precise negative voltage reference is desired, including the
AD8610 VOUT = 1.2V (1 + R2/R1)
application detailed in Figure 13.
ADR512W R2
Figure 14 shows the ADR512W configured to provide a −1.2 V output.
R1 C2 (OPTIONAL)
011 09938- Figure 11. Adjustable Precision Voltage Source Rev. 0 | Page 8 of 12 Document Outline Features Applications Pin Configuration General Description Revision History Specifications Electrical Characteristics Absolute Maximum Ratings Thermal Resistance ESD Caution Typical Performance Characteristics Terminology Applications Information Adjustable Precision Voltage Source Output Voltage Trim Using the ADR512W with Precision Data Converters Precise Negative Voltage Reference Outline Dimensions Ordering Guide Automotive Products