REF29xx 100 ppm/°C, 50 µA in 3-Pin SOT-23 CMOS Voltage Reference
1 Features
- MicroSIZE Package: SOT-23
- Low Dropout: 1 mV
- High Output Current: 25 mA
- Low Temperature Drift: Maximum of 100 ppm/°C
- High Accuracy: 2%
- Low IQ: Maximum of 50 µA
2 Applications
- Portable, Battery-Powered Equipment
- Data Acquisition Systems
- Medical Equipment
- Hand-Held Test Equipment
3 Description
The REF29xx is a precision, low-power, low-voltage dropout voltage reference family available in a tiny 3‑pin SOT-23 package.
The small size and low power consumption (50 µA maximum) of the REF29xx make it ideal for portable and battery-powered applications. The REF29xx does not require a load capacitor, but it is stable with any capacitive load.
Unloaded, the REF29xx can be operated with supplies within 1 mV of output voltage. All models are specified for the wide temperature range, –40°C to 125°C.
Device Information(1)
| PART NUMBER | PACKAGE | BODY SIZE (NOM) |
|---|---|---|
| REF29xx | SOT-23 (3) | 2.92 mm × 1.30 mm |
- For all available packages, see the orderable addendum at the end of the data sheet.
Dropout Voltage vs Load Current
4 Revision History
Changes from B Revision (February 2008) to C Revision
- Added ESD Ratings table, Thermal Information table, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information sectionGo
- Deleted Ordering Information table; see POA at the end of the data sheetGo
5 Device Comparison Table
| PRODUCT | VOLTAGE (V) |
|---|---|
| REF2912 | 1.25 |
| REF2920 | 2.048 |
| REF2925 | 2.5 |
| REF2930 | 3 |
| REF2933 | 3.3 |
| REF2940 | 4.096 |
6 Pin Configuration and Functions
Pin Functions
| PIN | I/O | DESCRIPTION | |
|---|---|---|---|
| NO. | NAME | ||
| 1 | IN | I | Input supply voltage |
| 2 | OUT | O | Reference output voltage |
| 3 | GND | — | Ground |
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)| MIN | MAX | UNIT | ||
|---|---|---|---|---|
| Supply voltage, V+ to V– | 7 | V | ||
| Output short circuit(2) | Continuous | °C | ||
| Lead temperature (soldering, 10 s) | 300 | °C | ||
| Operating temperature | –40 | 125 | °C | |
| Junction temperature | 150 | °C | ||
| Storage temperature, Tstg | –65 | 150 | °C | |
7.2 ESD Ratings
| VALUE | UNIT | |||
|---|---|---|---|---|
| V(ESD) | Electrostatic discharge | Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) | ±4000 | V |
| Charged-device model (CDM), per JEDEC specification JESD22-C101(2) | ±1500 | |||
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)| MIN | MAX | UNIT | ||
|---|---|---|---|---|
| VIN | Input voltage | VREF + 0.05(1) | 5.5 | V |
| ILOAD | Load current | 25 | mA | |
| TA | Operating temperature | –40 | 125 | °C |
7.4 Thermal Information
| THERMAL METRIC(1) | REF29xx | UNIT | |
|---|---|---|---|
| DBZ (SOT-23) | |||
| 3 PINS | |||
| RθJA | Junction-to-ambient thermal resistance | 297.3 | °C/W |
| RθJC(top) | Junction-to-case (top) thermal resistance | 128.5 | °C/W |
| RθJB | Junction-to-board thermal resistance | 91.7 | °C/W |
| ψJT | Junction-to-top characterization parameter | 12.8 | °C/W |
| ψJB | Junction-to-board characterization parameter | 90.3 | °C/W |
| RθJC(bot) | Junction-to-case (bottom) thermal resistance | N/A | °C/W |
7.5 Electrical Characteristics
Boldface limits apply over the specified temperature range, TA = –40°C to 125°C. At TA = 25°C, ILOAD = 0 mA, VIN = 5 V, unless otherwise noted.| PARAMETER | TEST CONDITIONS | MIN | TYP | MAX | UNIT | |
|---|---|---|---|---|---|---|
| REF2912 – 1.25 V | ||||||
| VOUT | Output voltage | 1.225 | 1.25 | 1.275 | V | |
| Initial accuracy | 2% | |||||
| Output voltage noise | f = 0.1 Hz to 10 Hz, | 14 | µVPP | |||
| Voltage noise | f = 10 Hz to 10 kHz | 42 | µVrms | |||
| Line regulation | 1.8 V ≤ VIN ≤ 5.5 V | 60 | 190 | µV/V | ||
| REF2920 | ||||||
| VOUT | Output voltage | 2.007 | 2.048 | 2.089 | V | |
| Initial accuracy | 2% | |||||
| Output voltage noise | f = 0.1 Hz to 10 Hz, | 23 | µVPP | |||
| Voltage noise | f = 10 Hz to 10 kHz | 65 | µVrms | |||
| Line regulation | VREF + 50 mV ≤ VIN ≤ 5.5 V | 110 | 290 | µV/V | ||
| REF2925 | ||||||
| VOUT | Output voltage | 2.45 | 2.5 | 2.55 | V | |
| Initial accuracy | 2% | |||||
| Output voltage noise | f = 0.1 Hz to 10 Hz | 28 | µVPP | |||
| Voltage noise | f = 10 Hz to 10 kHz | 80 | µVrms | |||
| Line regulation | VREF + 50 mV ≤ VIN ≤ 5.5 V | 120 | 325 | µV/V | ||
| REF2930 | ||||||
| VOUT | Output voltage | 2.94 | 3 | 3.06 | V | |
| Initial accuracy | 2% | |||||
| Output voltage noise | f = 0.1 Hz to 10 Hz, | 33 | µVPP | |||
| Voltage noise | f = 10 Hz to 10 kHz | 94 | µVrms | |||
| Line regulation | VREF + 50 mV ≤ VIN ≤ 5.5 V | 120 | 375 | µV/V | ||
| REF2933 | ||||||
| VOUT | Output voltage | 3.234 | 3.3 | 3.366 | V | |
| Initial accuracy | 2% | |||||
| Output voltage noise | f = 0.1 Hz to 10 Hz, | 36 | µVPP | |||
| Voltage noise | f = 10 Hz to 10 kHz | 105 | µVrms | |||
| Line regulation | VREF + 50 mV ≤ VIN ≤ 5.5 V | 130 | 400 | µV/V | ||
| REF2940 | ||||||
| VOUT | Output voltage | 4.014 | 4.096 | 4.178 | V | |
| Initial accuracy | 2% | |||||
| Output voltage noise | f = 0.1 Hz to 10 Hz, | 45 | µVPP | |||
| Voltage noise | f = 10 Hz to 10 kHz | 128 | µVrms | |||
| VREF + 50 mV ≤ VIN ≤ 5.5 V | 160 | 410 | µV/V | |||
| REF2912, REF2920, REF2925, REF2930, REF2933, REF2940 | ||||||
| dVOUT/dT | Output voltage temperature drift(2) | –40°C ≤ TA ≤ 125°C | 35 | 100 | ppm/°C | |
| ILOAD | Output current | 25 | mA | |||
| Long-term stability | 0 to 1000H | 24 | ppm | |||
| 1000 to 2000H | 15 | |||||
| dVOUT/dILOAD | Load regulation(3) | 0 mA < ILOAD < 25 mA, VIN = VREF + 500 mV(1) |
3 | 100 | µV/mA | |
| dT | Thermal Hysteresis(4) | 25 | 100 | ppm | ||
| VIN – VOUT | Dropout voltage | 1 | 50 | mV | ||
| ISC | Short-circuit current | 45 | mA | |||
| Turnon settling time | to 0.1% at VIN = 5 V with CL = 0 | 120 | µs | |||
| POWER SUPPLY | ||||||
| VS | Voltage | IL = 0 | VREF + 0.001(5) | 5.5 | V | |
| Voltage over temperature | –40°C ≤ TA ≤ 125°C | VREF + 0.05 | 5.5 | |||
| IQ | Quiescent current | 42 | 50 | µA | ||
| Quiescent current over temperature | –40°C ≤ TA ≤ 125°C | 59 | ||||
| TEMPERATURE RANGE | ||||||
| Specified range | –40 | 125 | °C | |||
| Operating range | –40 | 125 | °C | |||
| Storage range | –65 | 150 | °C | |||
| RθJC | Thermal resistance for SOT-23 surface-mount | 110 | °C/W | |||
| RθJA | 336 | °C/W | ||||
7.6 Typical Characteristics
8 Detailed Description
8.1 Overview
The REF29xx is a series, CMOS, precision band-gap voltage reference. Its basic topology is shown in Functional Block Diagram. The 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 R1. This voltage is gained up and added to the base-emitter voltage of Q2, which has a negative coefficient. The resulting output voltage is virtually independent of temperature. The curvature of the band-gap voltage, as seen in Figure 3, is due to the slightly nonlinear temperature coefficient of the base-emitter voltage of Q2.
8.2 Functional Block Diagram
Figure 24. Simplified Schematic of Band-Gap Reference
8.3 Feature Description
8.3.1 Supply Voltage
The REF29xx family of references features an extremely low dropout voltage. With the exception of the REF2912, which has a minimum supply requirement of 1.8 V, the REF29xx can be operated with a supply of only 1 mV above the output voltage in an unloaded condition. For loaded conditions, see Dropout Voltage vs Load Current.
The REF29xx features a low quiescent current, which is extremely stable over changes in both temperature and supply. The typical room temperature quiescent current is 42 µA, and the maximum quiescent current over temperature is just 59 µA. Additionally, the quiescent current typically changes less than 2.5 µA over the entire supply range, as shown in Figure 25.
Figure 25. Supply Current vs Supply Voltage
Supply voltages below the specified levels can cause the REF29xx to momentarily draw currents greater than the typical quiescent current. Using a power supply with a fast rising edge and low output impedance easily prevents this.
8.3.2 Thermal Hysteresis
Thermal hysteresis for the REF29xx is defined as the change in output voltage after operating the device at 25°C, cycling the device through the specified temperature range, and returning to 25°C, and can be expressed as shown in Equation 1.
where
- VHYST = calculated hysteresis
- VPRE = output voltage measured at 25°C pretemperature cycling
- VPOST = output voltage measured when device has been operated at 25°C, cycled through specified range –40°C to 125°C and returned to operation at 25°C
8.3.3 Temperature Drift
The REF29xx is designed to exhibit minimal drift error, defined as the change in output voltage over varying temperature. Using the box method of drift measurement, the REF29xx features a typical drift coefficient of 20 ppm from 0°C to 70°C— the primary temperature range of use for many applications. For industrial temperature ranges of –40°C to 125°C, the REF29xx family drift increases to a typical value of 50 ppm.
8.3.4 Noise Performance
The REF29xx generates noise less than 50 µVPP between frequencies of 0.1 Hz to 10 Hz, and can be seen in Figure 20. The noise voltage of the REF29xx increases with output voltage and operating temperature. Additional filtering may be used to improve output noise levels, however, take care ensuring the output impedance does not degrade AC performance.
8.3.5 Long-Term Stability
Long-term stability refers to the change of the output voltage of a reference over a period of months or years. This effect lessens as time progresses as is apparent by the long-term stability curves. The typical drift value for the REF29xx is 24 ppm from 0 to 1000 hours, and 15 ppm from 1000 to 2000 hours. This parameter is characterized by measuring 30 units at regular intervals for a period of 2000 hours.
8.3.6 Load Regulation
Load regulation is defined as the change in output voltage due to changes in load current. Load regulation for the REF29xx is measured using force and sense contacts as pictured in Figure 26. The force and sense lines tied to the contact area of the output pin reduce the impact of contact and trace resistance, resulting in accurate measurement of the load regulation contributed solely by the REF29xx. For applications requiring improved load regulation, force and sense lines must be used.
Figure 26. Accurate Load Regulation of REF29xx
8.4 Device Functional Modes
8.4.1 Negative Reference Voltage
For applications requiring a negative and positive reference voltage, the OPA703 and REF29xx can be used to provide a dual-supply reference from a ±5-V supply. Figure 27 shows the REF2925 used to provide a ±2.5-V supply reference voltage. The low offset voltage and low drift of the OPA703 complement the low drift performance of the REF29xx to provide an accurate solution for split-supply applications.
Figure 27. REF2925 Combined With OPA703 to Create Positive and Negative Reference Voltages
8.4.2 Data Acquisition
Often data acquisition systems require stable voltage references to maintain necessary accuracy. The REF29xx family features stability and a wide range of voltages suitable for most micro-controllers and data converters. See Figure 28 for a basic data acquisition system.
Figure 28. Basic Data Acquisition System 1
9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
9.1 Application Information
For normal operation, the REF29xx does not require a capacitor on the output. If a capacitive load is connected, take special care when using low equivalent series resistance (ESR) capacitors and high capacitance. This precaution is especially true for low-output voltage devices; therefore, for the REF2912 use a low-ESR capacitance of 10 µF or less. Figure 29 shows the typical connections required for operation of the REF29xx. TI always recommends a supply bypass capacitor of 0.47 µF.
Figure 29. Typical Connections for Operating REF29xx
9.2 Typical Application
Figure 30 shows a low-power reference and conditioning circuit. This circuit attenuates and level-shifts a bipolar input voltage within the proper input range of a single-supply low-power 16-bit ΔΣ ADC, such as the one inside the MSP430 or other similar single-supply ADCs. Precision reference circuits are used to level-shift the input signal, provide the ADC reference voltage and to create a well-regulated supply voltage for the low-power analog circuitry. A low-power, zero-drift, operational amplifier circuit is used to attenuate and level-shift the input signal.
Figure 30. Low-Power Reference and Bipolar Voltage Conditioning Circuit for Low-Power ADCs
9.2.1 Design Requirements
- Supply Voltage: 3.3 V
- Maximum Input Voltage: ±6 V
- Specified Input Voltage: ±5 V
- ADC Reference Voltage: 1.25 V
The goal for this design is to accurately condition a ±5-V bipolar input voltage into a voltage suitable for conversion by a low-voltage ADC with a 1.25-V reference voltage, VREF, and an input voltage range of VREF / 2. The circuit should function with reduced performance over a wider input range of at least ±6 V to allow for easier protection of overvoltage conditions.
9.2.2 Detailed Design Procedure
Figure 30 depicts a simplified schematic for this design showing the MSP430 ADC inputs and full input-conditioning circuitry. The ADC is configured for a bipolar measurement where final conversion result is the differential voltage between the voltage at the positive and negative ADC inputs. The bipolar, GND referenced input signal must be level-shifted and attenuated by the operational amplifier so that the output is biased to VREF / 2 and has a differential voltage that is within the ±VREF / 2 input range of the ADC.
9.2.3 Application Curves
