9.1 Overview

The REF19xx is a family of dual-output, V_REF and V_BIAS (V_REF / 2) band-gap voltage references. The Functional Block Diagram section provides a block diagram of the basic band-gap topology and the two buffers used to derive the V_REF and V_BIAS outputs. Transistors Q₁ and Q₂ are biased such that the current density of Q₁ is greater than that of Q₂. The difference of the two base emitter voltages (V_BE1 – V_BE2) has a positive temperature coefficient and is forced across resistor R₅. The voltage is amplified and added to the base emitter voltage of Q₂, which has a negative temperature coefficient. The resulting band-gap output voltage is almost independent of temperature. Two independent buffers are used to generate V_REF and V_BIAS from the band-gap voltage. The resistors R₁, R₂ and R₃, R₄ are sized such that V_BIAS = V_REF / 2.

e-Trim™ is a method of package-level trim for the initial accuracy and temperature coefficient of V_REF and V_BIAS, implemented during the final steps of manufacturing after the plastic molding process. This method minimizes the influence of inherent transistor mismatch, as well as errors induced during package molding. e-Trim is implemented in the REF19xx to minimize the temperature drift and maximize the initial accuracy of both the V_REF and V_BIAS outputs.

9.2 Functional Block Diagram

9.3 Feature Description

9.3.1 V_REF and V_BIAS Tracking

Most single-supply systems require an additional stable voltage in the middle of the analog-to-digital converter (ADC) input range to bias input bipolar signals. The V_REF and V_BIAS outputs of the REF19xx are generated from the same band-gap voltage as shown in the Functional Block Diagram section. Hence, both outputs track each other over the full temperature range of –40°C to 125°C with an accuracy of 7 ppm/°C (max). The tracking accuracy increases to 6 ppm/°C (max) when the temperature range is limited to –40°C to 85°C. The tracking error is calculated using the box method, as described by Equation 2:

Equation 2.

where

• 

The tracking accuracy is as shown in Figure 44.

Figure 44. V_REF and V_BIAS Tracking vs Temperature

9.3.2 Low Temperature Drift

The REF19xx 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, as described by Equation 3:

Equation 3.

9.3.3 Load Current

The REF19xx family is specified to deliver a current load of ±20 mA per output. Both the V_REF and V_BIAS outputs of the device are protected from short circuits by limiting the output short-circuit current to 50 mA. The device temperature increases according to Equation 4:

Equation 4.

where

• T_J = junction temperature (°C),
• T_A = ambient temperature (°C),
• P_D = power dissipated (W), and
• R_θJA = junction-to-ambient thermal resistance (°C/W).

The REF19xx maximum junction temperature must not exceed the absolute maximum rating of 150°C.

9.4 Device Functional Modes

When the EN pin of the REF19xx is pulled high, the device is in active mode. The device must be in active mode for normal operation. The REF19xx can be placed in a low-power mode by pulling the ENABLE pin low. When in shutdown mode, the output of the device becomes high impedance and the quiescent current of the device reduces to 5 µA in shutdown mode. See the Electrical Characteristics for logic high and logic low voltage levels.