‡

DIFF

REF

BIAS

V

V

2 V

DIFF(MAX)

DIFF (MIN)

6

REF

V

V

Tracking Error

10

(ppm)

V

Temperature Range

§

·

x

¨

¸

x

©

¹

+

+

e-Trim

e-Trim

+

VREF

VBIAS

R3

R4

R1

R2

Q1

Q2

VBE1

VBE2

-

-

+

+

R5

R7

R6

15

REF1925, REF1930, REF1933, REF1941

www.ti.com

SBOS697A – SEPTEMBER 2014 – REVISED JANUARY 2017

Product Folder Links: REF1925 REF1930 REF1933 REF1941

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Copyright © 2014–2017, Texas Instruments Incorporated

9 Detailed Description

9.1 Overview

The REF19xx is a family of dual-output, VREF and VBIAS (VREF / 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 VREF and VBIAS 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 (VBE1 – VBE2) 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 VREF and VBIAS from the band-gap voltage. The

resistors R1, R2 and R3, R4 are sized such that VBIAS = VREF / 2.

e-Trim™ is a method of package-level trim for the initial accuracy and temperature coefficient of VREF and VBIAS,

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 VREF

and VBIAS outputs.

9.2 Functional Block Diagram

9.3 Feature Description

9.3.1 VREF and VBIAS 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 VREF and VBIAS 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:

where

•

(2)