feature

Initial Accuracy: ±0.1% (max); Maximum Temperature Coefficient: 8ppm/°C; Operating Temperature Range: -40°C to +125°C Output Current: +10mA Source/-3mA Sink Low Quiescent Current: 100µA (max); Low Dropout: 250mV at 2mA; Output Noise (0.1 Hz to 10 Hz): <10µV pp (typ) at 1.2 V 6-lead SOT-23 .

application

Precision data acquisition systems; industrial instrumentation; battery-powered equipment for medical equipment.

General Instructions

The ADR3412 / ADR3420 / ADR3425 / ADR3430 / ADR3433 / ADR3440 / ADR3450 is a low cost, low power, high precision CMOS voltage reference with ±0.1% initial accuracy, low operating current and small SOT- 23 package output noise. For high accuracy, the output voltage and temperature coefficient are digitally trimmed during final assembly using patented DigiTrim® technology.

The output voltage lag of the device is small, and the long-term output voltage drift is small, which further improves the stability and reliability of the system. Additionally, the device's low operating current (100µA max) facilitates use in low power devices, and its low output noise helps maintain signal integrity in critical signal processing systems.

These CMOS are available in a wide range of output voltages, all specified over the industrial temperature range of -40°C to +125°C.

Absolute Maximum Ratings and Minimum Operating Conditions

T=25°C unless otherwise noted.

Stresses 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. Long-term exposure to absolute maximum rating conditions may affect device reliability.

Thermal resistance

θ is specified for the worst case, that is, a device soldered in a circuit board for a surface mount package.

Typical performance characteristics

T=25°C unless otherwise noted.

the term

Voltage drop (VDO)

Dropout voltage, sometimes referred to as supply voltage headroom or supply output voltage difference, is defined as the minimum voltage difference between the input and output to keep the output voltage within 0.1% accuracy.

Because the leakage voltage depends on the current through the device, it is always specified for a given load current. In series-mode devices, the leakage voltage typically increases in proportion to the load current (see Figures 8 and 14).

Temperature Coefficient (TCV OUT)

The temperature coefficient relates the change in the output voltage to the change in the ambient temperature of the device, normalized by the output voltage at 25°C. This parameter is expressed in ppm/°C and can be determined by the following equation:

Where: VOUT (T) is the output voltage at temperature T.

T1=-40 degrees Celsius.

T2=+25 degrees Celsius.

T3=+125 degrees Celsius.

This three-point method ensures that the TCV accurately depicts the maximum difference between the three temperatures at which the output voltage of the part is measured.

The TCV of ADR3412/ADR3425/ADR3430/ADR3433/ADR3440/ADR3450 is guaranteed by statistical methods. This was done by recording the output voltage data of a large number of over-temperature devices, calculating the TCV of each device via Equation 1, and then defining the maximum TCV limit as the average TCV of all devices, extended by six standard deviations (6σ).

Thermal Sensing Output Voltage Hysteresis (ΔVOUT_HYS) Thermal Sensing Output Voltage Hysteresis represents the change in output voltage after the device is exposed to a specified temperature cycle. This is expressed as voltage change or ppm difference from nominal output.

where: VOUT (25°C) is the output voltage at 25°C.

VOUT_TC is the output voltage after temperature cycling.

Long-term stability (ΔVOUT_LTD)

Long-term stability refers to the change in output voltage at 50°C after 1000 hours of operation in a 50°C environment. The ambient temperature was maintained at 50°C to ensure that the temperature chamber did not switch randomly between heating and cooling, which could cause instability in the 1000-hour measurement. This can also be expressed as voltage change or ppm difference from nominal output.

where: VOUT(t0) is VOUT at 50°C at time 0.

VOUT(t1) is VOUT at 50°C after 1000 hours of operation at 50°C.

Line conditioning

Line regulation is the change in output voltage in response to a given change in input voltage expressed as a percentage per volt, ppm per volt, or μV per volt of input voltage change. This parameter accounts for the effect of self-heating.

load regulation

Load regulation refers to the change in output voltage with a given change in load current in μV/mA, ppm/mA or DC output resistance ohms. This parameter accounts for the effect of self-heating.

Solder Heat Resistance (SHR) Drift

SHR drift is the permanent change in output voltage due to exposure to reflow soldering in ppm. This is due to the change in stress exhibited by the packaging material on the mold when exposed to high temperatures. This effect is more pronounced in lead-free soldering processes due to higher reflow temperatures.

theory of operation

ADR3412/ADR3425/ADR3430/ADR3433/ADR3440/

The ADR3450 uses a patented voltage reference structure to achieve high accuracy, low temperature coefficient (TC), and low noise in a CMOS process. Like all bandgap references, the reference combines the voltages of two opposing TCs to produce an output voltage that is virtually independent of ambient temperature. However, unlike conventional bandgap voltage references, the temperature-independent voltage of the reference is arranged to be the base-emitter voltage V of the bipolar transistor at room temperature, rather than the V extrapolated to 0k (the bipolar transistor at 0k The V is about V, the bandgap voltage of silicon). The corresponding positive TC voltage is then added to the V voltage to compensate for its negative TC. The main advantage of this technology is that the initial accuracy and TC can be fine-tuned without interfering with each other, thereby increasing the temperature. Curvature correction technology further reduces temperature variation.

Then, the bandgap voltage (V) is buffered and amplified to produce stable output voltages of 2.5 V and 5.0 V. The output buffer can generate up to 10mA of supply and can sink up to -3mA of load current.

The ADR34xx family utilizes patented analog device DigiTrim technology to achieve high initial accuracy and low TC, while precise layout techniques result in very low long-term drift and thermal hysteresis.

long-term stability

One of the key parameters of the ADR34xx references is long-term stability. Regardless of output voltage, internal testing during development showed a typical drift of approximately 30 ppm after 1000 hours of continuous no-load operation in a 50°C environment.

It is important to understand that long-term stability is not guaranteed by design, and the output of the device may exceed the typical 30ppm specification at any time, especially during the first 200 hours of operation. For systems that require a high, stable output voltage for long periods of time, designers should consider burning the device before use to minimize the amount of reference output drift over time. For more information on the effects of long-term drift and how to minimize it, see the AN-713 application note "Effects of Long-Term Drift on Voltage References" above.

Power consumption

The ADR34xx voltage references are capable of generating up to 10 mA of load current at room temperature over the rated input voltage range. However, when used in high ambient temperatures, the input voltage and load current should be carefully monitored to ensure the device does not exceed its maximum power dissipation rating. The maximum power consumption of the device can be calculated by the following formula:

In the formula: PD is the power consumption of the device.

TJ is the device junction temperature.

TA is the ambient temperature.

θJA is the thermal resistance of the package (connected to air).

Due to this relationship, the acceptable load current in high temperature conditions may be less than the maximum current source capability of the device. Under no circumstances should components be operated beyond their maximum power ratings as doing so could result in premature failure or permanent damage to the equipment.

application information

Reference voltage connection

The circuit shown in Figure 40 illustrates the basic configuration of the ADR34xx reference. The bypass capacitor connections should follow the guidelines below.

Input and output capacitors

A 1µF to 10µF electrolytic or ceramic capacitor can be connected to the input to improve transient response in applications where the supply voltage may fluctuate. To reduce high frequency power supply noise, a 0.1μF ceramic capacitor should also be connected in parallel.

A ceramic capacitor of at least 0.1µF must be connected to the output to improve stability and help filter out high frequency noise. A 1µF to 10µF electrolytic or ceramic capacitor can be added in parallel to improve transient performance during sudden changes in load current; however, designers should keep in mind that doing so will increase the turn-on time of the device.

Low ESR (eg less than 1Ω), low inductance ceramic chip output capacitors (X5R, X7R or similar) for best performance and stability. If an electrolytic capacitor is used at the output, a 0.1µF ceramic capacitor should be connected in parallel to reduce the overall ESR at the output.

4-wire KELVIN connection

The current flowing through the PCB trace creates an IR voltage drop, and as the trace lengthens, this voltage drop can reach a few millivolts or more, introducing considerable error to the reference's output voltage. At room temperature, the resistance of a 1-ounce copper wire 1 inch long and 5 mm wide is about 100 megohms; at a load current of 10 milliamps, this can result in a full millivolt error. In an ideal board layout, the reference should be mounted as close to the load as possible to minimize the length of the output traces, thereby reducing errors due to voltage drops. However, in applications where this is not possible or convenient, force and sense connections (sometimes referred to as Kelvin sense connections) are provided as a means of minimizing IR drop and improving accuracy.

Kelvin connections work by providing a set of high impedance voltage sensing lines to the output and ground nodes. Since there is very little current through these connections, the IR drop of the traces through them is negligible and the output voltage and ground voltage can be accurately detected. These voltages are fed back into an internal amplifier for automatic correction of the voltage drop between the current-carrying output and ground, resulting in a highly accurate output voltage across the load. For best performance, the sense connection should be connected directly to the point in the load where the output voltage is most accurate. See the example application in Figure 41.

It is always advantageous to use Kelvin connections whenever possible. However, in applications where the IR drop is negligible or cannot route an extra set of traces to the load, the force and sense pins of V and GND can simply be connected together and the device can be connected to a normal 3-terminal reference ( shown in Figure 40) in the same way.

Vin Slew Rate Considerations

In applications where the input voltage signal is slowly rising, the reference voltage can experience overshoot or other transient anomalies appearing at the output. These phenomena also occur during shutdown when the internal circuits are powered off.

To avoid this, make sure that the input voltage waveform has a rise and fall slew rate of at least 0.1V/ms.

Disable/enable feature

The ADR34xx references can switch to low power shutdown mode when 0.7 V or less is input to the enable pin. Likewise, when the enable voltage is 0.85×V or higher, the reference starts to work. During shutdown, the supply current drops to less than 5µA, which is useful in power-sensitive applications.

If using the shutdown function, make sure that the enable pin voltage is not between 0.7 V and 0.85 × V, as this will cause a large increase in the device's supply current and may cause the reference to start up incorrectly (see Figure 34). However, if the shutdown function is not used, the enable pin can simply be tied to the V pin and the reference remains in continuous operation. In the

sample application

negative reference

Figure 42 shows how to connect the ADR3450 and a standard CMOS op amp such as the AD8663 to provide a negative reference voltage. This configuration offers two main advantages: first, it requires only two devices and therefore does not require excessive board space; second, and more importantly, it does not require any external resistors, which means that the circuit's Performance does not depend on choosing expensive components with low temperature coefficients to ensure accuracy.

In this configuration, the V pin of the reference voltage is at virtual ground, and the negative reference voltage and load current are taken directly from the output of the op amp. Note that in applications where the negative supply voltage is close to the reference output voltage, a dual supply, low offset, rail-loop output amplifier must be used to ensure accurate output voltages. The op amp must also be able to source or sink the appropriate amount of current for the application.

Bipolar Output Reference

Figure 43 shows a bipolar reference configuration. The positive and negative reference voltages can be obtained by connecting the output of the ADR3450 to the inverting terminal of the op amp. R1 and R2 must be matched as closely as possible to ensure minimal difference between negative and positive outputs. Low temperature coefficient resistors must also be used if the circuit is used in an environment with large temperature fluctuations; otherwise, a voltage difference will develop between the two outputs as the ambient temperature changes.

Boost Output Current Reference

Figure 44 shows a configuration to obtain higher current drive capability from the ADR34xx reference without sacrificing accuracy. The op amp regulates the current through the MOSFET until V equals the output voltage of the reference voltage; it then draws current directly from V rather than the reference voltage itself, increasing the current drive capability.

Since the current sourcing capability of this circuit depends only on the I rating of the MOSFET, the output drive capability can be adjusted according to the application as long as the proper MOSFET is selected. In all cases, the Vsense pin should be connected directly to the load device to maintain maximum output voltage accuracy.

Dimensions

[1] Refers to the minimum difference between V and V to keep V with a minimum accuracy of 0.1%.

[2] See terminology section. Parts are placed throughout the temperature cycle in the temperature sequence shown.

[3] Refers to the minimum difference between V and V such that V maintains a minimum accuracy of 0.1%.

[4] See the Terminology section. Parts are placed throughout the temperature cycle in the temperature sequence shown.

[5] Refers to the minimum difference between V and V such that V maintains a minimum accuracy of 0.1%.

[6] See the Terminology section. Parts are placed throughout the temperature cycle in the temperature sequence shown.

[7] Refers to the minimum difference between V and V to keep V with a minimum accuracy of 0.1%.

[8] See the Terminology section. Parts are placed throughout the temperature cycle in the temperature sequence shown.

[9] Refers to the minimum difference between V and V to keep V with a minimum accuracy of 0.1%.

[10] See the Terminology section. Parts are placed throughout the temperature cycle in the temperature sequence shown.

[11] Refers to the minimum difference between V and V to keep V with a minimum accuracy of 0.1%.

[12] See the Terminology section. Parts are placed throughout the temperature cycle in the temperature sequence shown.

[13] See the Application Information section for more information on force/sensing connections.

[14] = RoHS compliant parts.