Datasheet ADR512 (Analog Devices) - 8

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ADR512 Data Sheet APPLICATIONS SECTION
The ADR512 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 ADR512 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 kΩ supply. potentiometer. As with all shunt voltage references, an external bias resistor
VCC
(RBIAS) is required between the supply voltage and the ADR512 (see Figure 2). R
R
BIAS sets the current that is required to pass
BIAS
through the load (I
V
L) and the ADR512 (IQ). The load and the
OUT
supply voltage can vary, thus R
POT
BIAS is chosen based on
ADR512 50kΩ R1
• R
100kΩ
BIAS must be smal enough to supply the minimum IQ 012 current to the ADR512 even when the supply voltage is at 03700- its minimum and the load current is at its maximum value. Figure 12. Output Voltage Trim • RBIAS also needs to be large enough so that IQ does not exceed 10 mA when the supply voltage is at its maximum
USING THE ADR512 WITH PRECISION DATA
and the load current is at its minimum.
CONVERTERS
The compact ADR512 package and the device’s low minimum Given these conditions, RBIAS is determined by the supply operating current requirement make it ideal for use in battery voltage (VS), the load and operating current (IL and IQ) of the powered portable instruments, such as the AD7533 CMOS ADR512, and the ADR512’s output voltage. multiplying DAC, that use precision data converters. RBIAS = (VS − VOUT)/(IL + IQ) (3) Figure 13 shows the ADR512 serving as an external reference to
ADJUSTABLE PRECISION VOLTAGE SOURCE
the AD7533, a CMOS multiplying DAC. Such a DAC requires a The ADR512, combined with a precision low input bias op amp negative voltage input in order to provide a positive output such as the AD8610, can be used to output a precise adjustable range. In this application, the ADR512 is supplying a −1.2 V voltage. Figure 11 il ustrates the implementation of this application reference to the REF input of the AD7533. using the ADR512.
0 9 + MSB LSB
The output of the op amp, VOUT, is determined by the gain of the
ADR512 VDD 1 – AD7533
circuit, which is completely dependent on resistors R2 and R1.
1
R2
GN
V = 1 + (4)
R2 3
OUT 1 R
2 1 15
An additional capacitor in parallel with R2 can be added to
–VDD +
filter out high frequency noise. The value of C2 is dependent on
VOUT = 0V TO 1.2V
the value of R2.
–
013 03700-
VCC
Figure 13. ADR512 as a Reference for a 10-Bit CMOS DAC (AD7533)
RBIAS 1.2V AD8610 VOUT = 1.2V (1 + R2/R1) ADR512 R2 R1 C2 (OPTIONAL)
1 1 0 03700- Figure 11. Adjustable Precision Voltage Source Rev. A | 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 Parameter Definitions Temperature Coefficient Thermal Hysteresis Applications Section Adjustable Precision Voltage Source Output Voltage Trim Using the ADR512 with Precision Data Converters Precise Negative Voltage Reference Outline Dimensions Ordering Guide