APPLICATION BULLETIN ® Mailing Address: PO Box 11400 • Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd. • Tucson, AZ 85706 Tel: (602) 746-1111 • Twx: 910-952-111 • Telex: 066-6491 • FAX (602) 889-1510 • Immediate Product Info: (800) 548-6132 LOW POWER SUPPLY VOLTAGE OPERATION OF REF102 10.0V PRECISION VOLTAGE REFERENCE By R. Mark Stitt (602) 746-7445 Two of the most important specifications for a voltage reference are noise and stability with time. The zener-based REF102 10.0V voltage reference has much better noise and stability than band-gap-based references. reference as shown in Figure 1. This allows the REF102 to be used on ±9V power supplies, for example. The minimum voltage for V+ is actually 6.4V (the output of the REF102 can operate within 1.4V of its positive supply). An advantage that band-gap-based references have in some applications is the ability to operate from lower voltage power supplies. This is because the basic band gap voltage is approximately 1.2V as compared to 6V to 8V for a zener diode. As a 10.0V reference, the REF102 requires a minimum 11.4V VS. If the higher performance of a REF102 is required, there are several options for operation on lower supply voltages. If a negative supply is available, it may be possible to operate the REF102 on a positive supply as low as 4.5V. Another option is to use one of the simple DC/DC converter circuits shown to operate the REF102 from a single +5V power supply. The minimum negative supply depends on the amplifier used for the unity-gain inverter. With an INA105 difference amp used for the unity-gain inverter, the negative power supply must be at least –8V. To operate the REF102 on a minimum +VS of 4.5V, use an INA106 gain-of-10 difference amplifier for the inverter as shown in Figure 2. With the INA106, the reference outputs are +1.0V and –9.0V. The 4.5V minimum +VS rating is due to the output swing limit of the INA106. The negative supply must be at least –12V. V+ (4.5V min) The simplest option for reduced supply operation of a REF102 is to add a unity-gain inverter to make a ±5.0V 2 V+ REF102 V+ (6.4V min) +10V 6 Out 2 V+ +1.0V Out Gnd 4 REF102 +10V 6 Out –9.0V Out 7 +5.0V Out 5 R2 100kΩ R1 10kΩ 2 Gnd 4 –5.0V Out 7 5 R2 25kΩ R1 25kΩ R4 100kΩ 6 1 2 R3 10kΩ INA106 6 4 V– (–12V min) R4 25kΩ R3 25kΩ INA105 4 3 3 FIGURE 2. +1.0V, –9.0V Reference Using REF102 Can Operate on +VS = +4.5V, –VS = –12V. 1 V– (–8V min) FIGURE 1. ±5.0V Reference Using REF102 Can Operate on +VS = +6.4V, –VS = –8V. 1990 Burr-Brown Corporation AB-011 Printed in U.S.A. June, 1990 When only a single +5V power supply is available, the REF102 can be operated by boosting the 5V supply with one of the many inexpensive DC/DC converter chips available. A single 5V supply can be boosted to a regulated 15V with a flyback converter as shown in Figure 3. The Maxim MAX643 is basically a self-contained DC/DC converter in an 8-pin plastic DIP. The only additional components needed to convert 5V to a regulated 15V are a single external inductor and a few bypass capacitors. R6 and C3 add additional ripple filtering. Good results were obtained with an inductor made from 16 turns of #16 wire on a TDK HC52 T5-10-2.5 core. See the Maxim data sheet for more information regarding the DC/DC converter. +5V NC 10µF NC + NC NC MAXIM MAX681 0.1µF +10V Out NC 2 NC V+ –10V Out REF102 +10V 6 Out Another option is to boost a single 5V supply to ±10V to drive a ±5.0V reference as shown in Figure 4. The Maxim MAX681 is a completely self-contained DC/DC converter using charge-pump techniques to convert 5V to ±10V. Gnd 4 7 5 1mH 16 Turns #26 Wire on TDK HC52 T5-10-2.5 +5.0V Reference Out R2 25kΩ R1 25kΩ 2 –5.0V Reference Out +5V + 6 10µF NC NC R3 25kΩ INA105 4 3 MAXIM MAX643 R4 25kΩ 1 NC = Make No External Connection NC FIGURE 4. ±5.0V Reference Using REF102 Can Operate on Single +5V Power Supply. C1 R6 100Ω 100pF 2 V+ REF102 C3 1µF Tantalum + + C2 1µF Tantalum +10V 6 Out +10.0V Out Gnd 4 FIGURE 3. +10.0V Reference Using REF102 Can Operate on Single +5V Power Supply. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. 2