ADR1399

ADR1399 (Rev. A)

Document overview

• Manufacturer or author: Analog Devices, Inc.
• PDF pages: 16

Technical content

analog.com Rev. A | 2 of 16 Shunt Dynamic Impedance and Capacitive

REVISION HISTORY

3/2022—Rev. 0 to Rev. A Changes to Change in Reference Voltage with Current Parameter; Dynamic Impedance Parameter; 10/2021—Revision 0: Initial Version

analog.com Rev. A | 3 of 16

ELECTRICAL CHARACTERISTICS

TA = 25°C, unless otherwise noted. Table 2. Parameter Symbol Test Conditions/Comments Min Typ Max Unit ZENER REFERENCE VOLTAGE VZ 3 mA ≤ reference current (IREF) ≤ 13 mA 6.75 7.05 7.30 V CHANGE IN REFERENCE VOLTAGE WITH CURRENTΔVZ TO-46, 3 mA ≤ IREF ≤ 13 mA 0.4 0.8 mV LCC 0.11 0.25 mV DYNAMIC IMPEDANCE RZ TO-46, 3 mA ≤ IREF ≤ 13 mA 0.04 0.08 Ω LCC 0.011 0.025 Ω TEMPERATURE COEFFICIENT dV/dT IREF = 3 mA, heater voltage (VH) = 30 V, TA = 0℃ to 70°C 0.2 11 ppm/°C REFERENCE NOISE eN p-p IREF = 3 mA, 0.1 Hz < f < 10 Hz 0.2 ppm p-p IREF = 3 mA, 0.1 Hz < f < 10 Hz 1.44 µV p-p eN rms 10 Hz < f < 1 kHz 1.84 µV rms eN IREF = 3 mA Frequency = 0.1 Hz 200 nV/√Hz Frequency = 10 Hz 65 nV/√Hz Frequency = 1 kHz 58 nV/√Hz LONG-TERM STABILITY dVZ /dt VH = 30 V, 22°C ≤ TA ≤ 28°C, 1000 Hrs, IREF = 3 mA 7 ppm/√kHr HEATER SUPPLY CURRENT, STILL AIR2 IH TO-46, TA = 25°C, VH = 30 V, IREF = 3 mA 8.5 15 mA TA = –55°C 21 281 mA LCC, TA = 25°C, VH = 30 V, IREF = 3 mA 20 25 mA TA = –55°C 40 mA HEATER START-UP CURRENT IHS VH = 9.5 V to 30 V 110 140 mA HEATER SUPPLY VOLTAGE VH 9.5 40 V WARM-UP TIME tHOT TO-46, LCC socketed, to ±0.05%, VH = 30 V 0.1 sec To ±20 ppm 1 sec To ±10 ppm 5 sec 1 Guarantee by design, not 100% production tested. 2 Guarantee correlated to moving air production test.

ing conditions for extended periods may affect product reliability. PCB thermal design is required. Table 4. Thermal Resistance 1 The TO-46 case is not accessible beneath the Valox enclosure. damage may occur on devices subjected to high energy ESD. performance degradation or loss of functionality.

analog.com Rev. A | 11 of 16 OPERATING SET TEMPERATURE The ADR1399 contains a buried Zener diode with an approximate +2 mV/℃ temperature coefficient, in series with an NPN, base emitter voltage (VBE) with an approximate –2 mV/℃ temperature coefficient. The combined positive and negative temperature coeffi- cients sum to a nominal 0 mV/℃ overall temperature coefficient. There are two op-amp servo loops inside the ADR1399. One op-amp loop maintains a fixed ratio of Zener and VBE currents, with the total current set by an externally applied pull-up resistor or current source. Another op-amp loop maintains the device die at a nonadjustable set temperature of approximately 95℃ , precluding the external ambient temperature fluctuations from affecting operat- ing temperature. The entire system is provided in a simple 4-pin, hermetically sealed, TO-46 package and placed inside a plastic thermal insulator, which further keeps ambient fluctuations at bay and reduces the required heater power. If the ambient temperature exceeds the set temperature, the chip temperature control becomes open loop, and the temperature rejection of the device degrades while the excess ambient temperature condition persists. With only an external supply and a pull-up resistor required for operation, the ADR1399 is simple to use. However, because it is so extremely stable, care must be taken to avoid degrading overall performance with external thermocouples and/or IR drops. For example, the heater current can be quite high; therefore, avoid sharing the heater current path with the Zener sense path. In addition, wherever metallurgic junctions are formed, such as where the device pins enter the board or where the reference voltage may be connectorized, try to ensure that junctions are paired and with similar thermal gradients. Parasitic thermocouples can simply add temperature dependencies from 1 μV/℃ up to 40 μV/℃ . See Appli- cation Note 86, A Standards Lab Grade 20-Bit DAC with 0.1ppm/°C Drift for additional information on thermoelectric potentials. THERMAL RESISTANCE The ADR1399 has an on-chip automated heater set to approxi- mately 95°C. The TO-46 comes from the factory provided with a small plastic shield to keep air flow away from the reference. The factory included plastic air shield around the TO-46 reduces the effective net thermal resistance compared to a TO-46 without a shield. Techniques to increase thermal resistance include reducing solid copper planes in proximity to the device and elevating the device on its leads, approximately 1 cm above the board surface. A hatch ground on the bottom side of the board increases thermal resistance compared to a solid ground plane. The heater power for the LCC version is about 3× to 4× greater than the TO-46 version. To reduce heater power, keep copper away from the inner layers near the device and use a hatch ground on the bottom layer. The slotting method (Application Note 82, Understanding and Applying Voltage References), which was originally intended to isolate references from externally applied flexing on the board, helps to increase thermal resistance. Combining a copper keepout area, hatching the bottom side ground layer, and extreme slotting or isothermal islands keeps the PCB from drawing excessive heat from the ovenized reference. After assembly, an external enclosure or insulation can further reduce the heat loss and consequent power draw. FORCE AND SENSE PINS The LCC version adds four pins, two of which are not internally con- nected (NIC) and the other two split the active reference into force and sense action on the top and bottom of the shunt. The force pins (+REFF and −REFF) are similar to op amp outputs, and the sense pins (+REFS and −REFS) are similar to the feedback pins of an op amp in that they sense the output to close the feedback loop. However, they differ from op amps because the sense pins have 2.2 mA of bias current, which is orders of magnitude more than any op amp input, for example. Additionally, whereas an op amp is often designed in to have the output node at the correct voltage, the ADR1399 is designed to have the sense node at the most accurate voltage. For example, when some resistance is placed between the +REFF and +REFS pins, all the IR drop induced in the resistance, including the IR noise induced by approximately 10 pA/rtHz of current noise, is transferred to the +REFF pin and does not appear at the +REFS pin. For the most accurate reading of the reference voltage, sense the reference voltage at the +REFS and −REFS pins, and not at the force pins. The ADR1399 is characterized typically at 3 mA, and between 3 mA and 10 mA. Of the 3 mA, 2.2 mA is allocated to the ±REFS pins. 2.2 mA flows into the +REFS pin, and 2.2 mA flows out of the −REFS pin. The typical 3 mA is composed of an additional 0.8 mA flowing in and out of the +REFF and −REFF pins, respectively. At 10 mA, the sense pins remain at 2.2 mA and the extra 7.8 mA is regulated by the force pins.

Figure 35. LCC vs. TO-46 Block Diagrams

Figure 41. Basic Connections Using LCC with Force/Sense Pins

©2021-2022 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. One Analog Way, Wilmington, MA 01887-2356, U.S.A. Rev. A | 16 of 16 Updated: December 11, 2021 ORDERING GUIDE Model1 Temperature Range Package Description Package Option ADR1399KHZ 0°C to +70°C 4-Lead TO-46 05-08-1341 ADR1399KEZ 0°C to +70°C 8-Terminal LCC E-8-2 1 Z = RoHS Compliant Part. EVALUATION BOARDS Model1 Description ADR1399E-EBZ Evaluation Board for the ADR1399, LCC Package ADR1399H-EBZ Evaluation Board for the ADR1399, TO Package 1 Z = RoHS Compliant Part.