feature

Initial Accuracy: ±5 mV/±6 mV Maximum Initial Accuracy Error ±0.24% ±0.24%; Low TCVOUT: 25 ppm/°C Maximum Load Regulation: 70 ppm/mA Line Regulation: 25 ppm/v; Wide Operating Range; ADR380 2.4 V to 18 V; 2.8 V to 18 V for ADR381; low power consumption: 120 μA max; high output current: 5 mA; wide temperature range: –40°C to +85°C; Three-lead SOT-23 package.

application

Battery powered instruments; portable medical devices; data acquisition systems; industrial process control systems; automotive hard drives.

General Instructions

The ADR380 and ADR381 are 2.048V and 2.500V accurate bandgap voltage references featuring high accuracy, high stability, and low power consumption. A patented temperature drift curvature correction technique minimizes voltage nonlinearity with temperature. Wide operating range and low power consumption make them ideal for 3V to 5V battery powered applications.

The ADR380 and ADR381 are micropower, low voltage drop (LDV) devices that provide regulated output voltages as low as 300 mV from the output voltage. They are specified over the industrial (-40°C to +85°C) temperature range. The ADR380/ADR381 are available in a tiny 3-lead SOT-23 package.

Typical performance characteristics

the term

Temperature Coefficient

Change in output voltage as operating temperature changes, normalized by output voltage at 25°C, in ppm/°C. The formula is as follows:

Where: VOUT(25°C) = VOUT at 25°C. VOUT(T1) = VOUT at temperature 1. VOUT(T2) = VOUT at temperature 2.

Line conditioning

The change in output voltage due to a specific change in input voltage. It includes self-heating effects. Line regulation is expressed in percent per volt, parts per million per volt, or microvolts per volt of input voltage change.

load regulation

The change in output voltage due to a specific change in load current. It includes self-heating effects. Load regulation is expressed in microvolts per milliamp, millionths per milliamp, or DC output resistance in ohms.

long-term stability

The typical change in output voltage is over 1000 hours at controlled temperature. Figures 24 and 25 show part samples measured at various intervals for 1000 hours in a controlled environment at 50°C.

Where: VOUT(t0) = VOUT at time 0. VOUT(t1) = VOUT temperature after 1000 hours of operation under controlled conditions.

Note that 50°C was chosen because most applications are above 25°C.

thermal hysteresis

Change in output voltage of the device after cycling the temperature from +25°C to -40°C to +85°C and back to +25°C. This is typical for a sample of parts going through such a cycle.

Where: VOUT(25°C) = VOUT at 25°C. VOUT_TC = from +25°C to -40°C to +85°C and back to +25°C.

theory of operation

Bandgap references are a high-performance solution for low supply voltage and low power voltage reference applications, and the ADR380/ADR381 are no exception. However, what makes this product unique is its architecture. As shown in Figure 26, the ideal zero TC bandgap voltage refers to the output, not to ground. The bandgap unit consists of the PNP pair Q51 and Q52, operating at different current densities. The difference in V results in the positive TC of the voltage being amplified by the ratio of 2× R58 /R54. This PTAT voltage combines with the voltages of Q51 and Q52 to produce a stable bandgap voltage. The bandgap curvature is reduced by the ratio of the two resistors R44 and R59. Adopt patented circuit technology such as precision laser trimming to further improve drift performance.

Device Power Consumption Considerations

The ADR380/ADR38 1 are capable of delivering load currents up to 5 mA with input voltages ranging from 2.8 V (ADR38 1) to 15 V. When the device is used in applications with large input voltages, care should be taken to avoid exceeding the specified maximum power dissipation or junction temperature, which may result in premature device failure. Use the following formula to calculate the maximum junction temperature or loss of the device:

where: PD is the power dissipation of the device, and TJ and TA are the junction temperature and ambient temperature, respectively. θJA is the thermal resistance of the device package.

input capacitor

The ADR380/ADR381 do not require input capacitors. There is no limit to the value of the capacitor used on the input, but in applications where the load current suddenly increases, the capacitor on the input improves the transient response.

output capacitor

The ADR380/ADR381 do not require output capacitors for stability under any load conditions. Using an output capacitor (typically 0.1µF) removes any very low noise voltage without affecting the operation of the part. The only parameter is to reduce the power-on time by applying an output capacitor. (This depends on the size of the capacitor) Load transient response is also improved by the output capacitor, which acts as a storage source for sudden increases in load current.

application information

Stacked Reference ICs for Arbitrary Outputs

Some applications may require two voltage references, which are the combined sum of the standard outputs. The circuit below shows how to implement this superimposed output reference:

Use two ADR380s or ADR381s; the outputs of a single reference are simply cascaded to reduce supply current. This configuration provides two output voltages: V and output 1V, V is the terminal voltage of U1, and V is the sum of this voltage and the terminal voltage of U2. U1 and U2 can be used to provide two different voltages for the desired output. Output 2 Output 1 Output 2 While the concept is simple, precautions are necessary. Because the lower reference circuit must receive a small bias current from U2, plus the base current from the series PNP output transistor in U2, an external load from U1 or R1 must provide a path for this current. If the U1 minimum load is not well defined, resistor R1 should be used and set to pass 600 μA conservatively with an appropriate value of V across it. Note that the two U1 and U2 reference circuits are locally treated as macrocells, each with its own bypass at the input and output for optimum stability. Both U1 and U2 in this circuit can provide maximum rated DC current. The minimum input voltage V is determined by the sum of the output voltage V plus the 300 mV of U2.

Negative precision reference without precision resistors

In many current output CMOS DAC applications where the output signal voltage must have the same polarity as the reference voltage, it is often necessary to reconfigure the current switching DAC as a voltage switching DAC by using a 1.25v reference voltage, an op amp, and a pair of resistors. Using a current switching DAC directly requires adding an op amp at the output to reinject the signal. Therefore, a negative voltage reference is desirable from the standpoint that no additional op amps are required for reconversion (current switch mode) or amplification (voltage switch mode) of the DAC output voltage. In general, any positive voltage reference can be converted to a negative voltage reference by using an op amp and a pair of matched resistors in an inverse configuration. The disadvantage of this approach is that the largest single source of error in the circuit is the relative matching of the resistors used.

The circuit in Figure 28 avoids the need for closely matched resistors when using an active integrator circuit. In this circuit, the output of the voltage reference provides the input drive for the integrator. To keep the circuit balanced, the integrator adjusts its output to establish the proper relationship between the reference voltage and GND. Therefore, any negative output voltage desired can be selected by substituting the appropriate reference IC. One precaution should be taken with this approach: While rail-to-rail output amplifiers work best in the application, these op amps require limited (mV) headroom when needed to supply any load current. The choice of the negative power supply of the circuit should take this issue into account.

Precision Current Source

Many times in low power applications, a precision current source that can operate at low supply voltages is required. As shown in Figure 29, the ADR380/ADR381 can be configured as precision current sources. The circuit configuration shown is a floating current source with a grounded load. The reference output voltage is bootstrapped through R(R1+P1), which sets the output current into the load. With this configuration, the accuracy of the circuit remains within the range of the load current from the reference supply current, typically 90µA to about 5mA.

Precision high current voltage source

In some cases, the user may wish to supply higher output current to the load and still obtain better than 0.5% accuracy from the ADR380/ADR381. The accuracy of the reference is usually specified in the datasheet, no load. However, the output voltage varies with load current.

The circuit in Figure 30 delivers high current without compromising the accuracy of the ADR380/ADR381. Through the action of the op amp, V follows V and R1 drops very low. To keep the circuit balanced, the op amp also drives the N-channel MOSFET Q1 into saturation to maintain the required current under different loads. R2 is optional to prevent oscillations in Q1. In this approach, load currents in the hundreds of milliamps can be obtained, and the current is limited by the thermal limitations of Q1. V=V+300mV.

Dimensions