Avoiding Excessive Supply Current in the HS-1840ARH During Start-Up ® Technical Brief January 2003 Description TB402 Schematic If the supply voltages (+Vs and -Vs) and reference voltage (Vref) to the HS-1840ARH are not sequenced properly, it is possible that excessive supply current will flow during startup. The maximum current that can flow from either supply is 30mA as long as the supply voltages are limited to ±16.5V. Up to 40mA can flow from either supply if the supply voltages reach ±20V. Although this condition is not harmful to the part, it can cause system problems if this current is not included in the power supply budget. The internal level-shifter in the HS-1840ARH is referenced to the negative supply and requires a voltage on Vref of at least 1.2V to initialize its state. If the level-shifter circuitry is not initialized, the part can start drawing excessive supply current once the supply voltages reach about ±5V. With the previous generation HS-1840RH, the level-shifter was referenced to ground and did not require a voltage on Vref in order to initialize. +15V OUT 28 1 +Vs 2 NC -Vs 27 3 NC IN 8 26 4 IN 16 IN 7 25 5 IN 15 IN 6 24 6 IN 14 IN 5 23 7 IN 13 IN 4 22 8 IN 12 IN 3 21 9 IN 11 IN 2 20 10 IN 10 -15V IN 1 19 11 IN 9 ENABLE 18 12 GND ADDR A0 17 13 VREF ADDR A1 16 14 ADDR A3 ADDR A2 15 The voltage on the Vref pin sets the logic threshold level of the input address decode circuitry and should be set to 5V ±10%. Under recommended operating conditions, Vref typically consumes about 22µA of current, but to account for variations over voltage, temperature and radiation, we recommend that 50µA be allocated. The easiest way to prevent excessive supply current during start-up is to derive the reference voltage from the positive supply voltage. This can easily be accomplished using a zener diode and a resistor as shown in the schematic diagram. For application assistance on this or any other Intersil radiation hardened ICs, please feel free to contact us at the web address shown below. www.intersil.com/tsc All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com 1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright © Intersil Americas Inc. 2003. All Rights Reserved All other trademarks mentioned are the property of their respective owners.