8.3.1 Supply Voltage

The REF50xxA-Q1 family of voltage references features extremely low dropout voltage. With the exception of the REF5020A-Q1 device, which has a minimum supply requirement of 2.7 V, these references can operate with a supply of 200 mV above the output voltage in an unloaded condition. For loaded conditions, Figure 6 in the Typical Characteristics section shows a typical dropout voltage versus load plot.

8.3.2 Using the TRIM/NR Pin

The REF50xxA-Q1 family of devices provides a very accurate voltage output. However, V_OUT can be adjusted to reduce noise and shift the output voltage from the nominal value by configuring the trim and noise reduction pin (TRIM/NR, pin 5). The TRIM/NR pin provides a ±15-mV adjustment of the device bandgap, which produces a ±15-mV change on the V_OUT pin. Figure 25 shows a typical circuit using the TRIM/NR pin to adjust V_OUT. When using this technique, the temperature coefficients of the resistors can degrade the temperature drift at the output.

Figure 25. V_OUT Adjustment Using TRIM/NR Pin

The REF50xxA-Q1 family of devices allows access to the bandgap through the TRIM/NR pin. Placing a capacitor from the TRIM/NR pin to GND (as shown in Figure 26) in combination with the internal 1-kΩ resistor creates a low-pass filter that lowers the overall noise measured on the V_OUT pin. A capacitance of 1 μF is suggested for a low-pass filter with a corner frequency of 14.5 Hz. Higher capacitance results in a lower cutoff frequency.

Figure 26. Noise Reduction Using TRIM/NR Pin

8.3.3 Temperature Drift

The REF50xxA-Q1 family of devices is designed for minimal drift error, which is defined as the change in output voltage over temperature. The drift is calculated using the box method. Use Equation 1 to calculate the drift.

Equation 1.

The REF50xxA-Q1 family of devices features a maximum drift coefficient of 8 ppm/°C for the standard-grade.

8.3.4 Temperature Monitoring

The temperature output pin (TEMP, pin 3) provides a temperature-dependent voltage output with approximately 60-kΩ source impedance. As shown in Figure 8, the output voltage follows the nominal relationship:

This pin indicates general chip temperature, accurate to approximately ±15°C. Although this pin is not generally suitable for accurate temperature measurements, it can be used to indicate temperature changes or for temperature compensation of analog circuitry. A temperature change of 30°C corresponds to an approximate 79-mV change in voltage at the TEMP pin.

The TEMP pin has high output impedance (see the Functional Block Diagram section). Loading this pin with a low-impedance circuit induces a measurement error; however, it does not have any effect on V_OUT accuracy.

To avoid errors caused by low-impedance loading, buffer the TEMP pin output with a suitable low-temperature drift op amp, such as the OPA333, OPA335, or OPA376, as shown in Figure 27.

1. Low drift op amp, such as the OPA333, OPA335, or OPA376 device.

Figure 27. Buffering the TEMP Pin Output