feature

Accuracy 1. 200 V voltage reference; ultra-compact 3 mm × 3 mm SOT-23 package without external capacitors; low output noise: 4 microvolts pp (0.1 Hz to 10 Hz); initial accuracy: ±0.3% max; temperature Coefficient: 60 ppm/°C max; Operating Current Range: 100µA to 10mA; Output Impedance: 0.3Ω max; Temperature Range: -40°C to +85°C.

application

Precision data acquisition systems Battery-powered equipment: cell phones, laptops, PDAs, and GPS; 3 V/5 V, 8/12-bit data converters; portable medical devices; industrial process control systems; precision instruments.

General Instructions

The ADR512 is a low-voltage (1.200 V) precision shunt-mode voltage reference in an ultra-small (3 mm × 3 mm) SOT-23 package designed for space-critical applications. The ADR512 features low temperature drift (60 ppm/°C), high accuracy (±0.30%), and ultralow noise (4 μV pp).

The advanced design of the ADR512 eliminates the need for external capacitors, yet it is stable with any capacitive load. The minimum operating current is increased from less than 100 microamps to a maximum of 10 milliamps. This low operating current and ease of use make the ADR512 ideal for handheld battery powered applications.

There is a trim terminal on the ADR512 to adjust the output voltage to more than ±0.5% without affecting the temperature coefficient of the device. This feature provides the user with the flexibility to eliminate any system errors.

Specification

Electrical Characteristics

IIN = 100µA to 10mA @TA = 25°C unless otherwise noted.

Absolute Maximum Ratings

Stresses listed above the Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device under the conditions described in the operating section of this specification or any other conditions above is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

Thermal resistance

θJA is specified for worst-case, devices soldered in circuit boards intended for surface mount packages.

Typical performance characteristics

parameter definition

Temperature Coefficient

This is the change in output voltage relative to a change in operating temperature, normalized by the output voltage at 25°C. This parameter is expressed in ppm/°C and can be determined by the following equation:

Where: VO(25c) = VO at 25°C VO(T1) = VO at 1°C; VO(T2) = VO at temperature 2.

thermal hysteresis

Thermal hysteresis is defined as the change in output voltage of the device after cycling at +25°C to -40°C to +85°C and back to +25°C. This is a typical value extracted from a sample of parts going through such a cycle.

Among them, VO (25 (C) = 25 (C) VO, after 25.C. temperature cycle, from +25.C. to +85.C. and back to +25.C.

application section

The ADR512 is a 1.2V precision shunt voltage reference. It is designed to operate without an external output capacitor between positive and negative for stability. External capacitors can be used for additional filtering of the power supply. As with all parallel voltage references, the external bias resistor (R) is required between the supply voltage and the ADR512 (see Figure 2). The RBIAS sets the current required through the load (IL) and the ADR512 (IQ). Load and supply voltages can vary, so the RBIA is chosen based on the bias RBIAS must be small enough to provide the minimum IQ current to the ADR512 even when the supply voltage is at a minimum value and the load current is at a maximum value.

RBIAS also needs to be large enough so that IQ does not exceed 10mA when the supply voltage is at its maximum value and the load current is at its minimum value.

Given these conditions, rbia is determined by the ADR512's supply voltage (VS), load and operating currents (IL and IQ), and the ADR512's output voltage.

Adjustable Precision Voltage Source

The ADR512, combined with a precision low input bias op amp such as the AD8610, can be used to output a precisely adjustable voltage. Figure 11 illustrates the implementation of this application using the ADR512.

The output of the op amp, VOUT, is determined by the gain of the circuit, which is completely dependent on resistors R2 and R1.

Additional capacitors in parallel with R2 can be added to filter out high frequency noise. The value of C2 depends on the value of R2.

Output voltage trimming

Using a mechanical or digital potentiometer, the output voltage of the ADR512 can be adjusted to ±0.5%. The circuit in Figure 12 illustrates how to use a 10 kΩ potentiometer to adjust the output voltage.

Using the ADR512 with Precision Data Converters

The compact ADR512 package and the device's low minimum operating current requirements make it ideal for battery-powered portable instruments that use precision data converters, such as the AD7533 CMOS multiplying DAC.

Figure 13 shows the ADR512 as an external reference to the AD7533 (CMOS multiplying DAC). Such DACs require a negative voltage input to provide a positive output range. In this application, the ADR512 provides a -1.2v reference voltage to the REF input of the AD7533.

Accurate Negative Voltage Reference

The ADR512 is suitable for applications that require an accurate negative voltage reference, including those detailed in Figure 13.

Figure 14 shows the ADR512 configured to provide a -1.2V output.

Since the characteristics of the ADR512 are similar to those of a Zener diode, the cathode shown in Figure 14 will be 1.2V higher relative to the anode (relative to V-, V+ on the ADR512 package). Since the cathode of the ADR512 is grounded, the anode must be -1.2V.

R1 in Figure 14 should be chosen to provide 100µA to 10mA to properly bias the ADR512.

Resistor R1 should be chosen to minimize power dissipation. An ideal resistance value can be determined by manipulating Equation 5.