13814994AN591| Application Note
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AN-591 APPLICATION NOTE
ADM1070 Hot Swap Controller
by Alan Moloney
One Technology Way P.O. Box 9106 Norwood, MA 02062-9106 Tel: 781/329-4700 Fax: 781/326-8703 www.analog.com
The ADM1070 is a negative voltage ( 48 V) hot swap controller. The device provides robust current limiting, protects against transient and nontransient short circuits, and offers single-pin undervoltage and overvoltage protection. The ADM1070 has many applications, such as central office switching, 48 V distributed systems, and negative power supply control. This application note describes the operation of the ADM1070 under various hot swap insertion and removal conditions. This document should be consulted in conjunction with the ADM1070 data sheet and evaluation board documentation. All of the tests described in this document can be recreated with the ADM1070 evaluation board.
LONG CONNECTOR RDROP 16k VIN VOUT
The ADM1070 is designed to reside on a plug-in board or a live backplane and uses a FET in the power path to control the load current. It requires a few other external components to operate, such as a shunt resistor, two divider resistors, and a SENSE resistor. A 16 k shunt resistor is required between the 0 V line and the VIN pin to power the part. Resistors R1 and R2 form a resistor divider that scales down the supply voltage to a range that the device can measure. The divider output is used for undervoltage/ overvoltage detection at the UV/OV pin. By choosing the values of R1 and R2 carefully, the part can be programmed to apply the supply voltage to the load only when the supply is in the desired range. The default evaluation board resistor values give an operating range of around 36 V to 77 V. Please refer to Table IV of the ADM1070 data sheet for a full description of how the operating voltage window can be programmed. The SENSE resistor, RSENSE, is used for current limiting. The ADM1070 continually
senses the voltage across RSENSE and can detect whether the load current is above the maximum permitted load current value. If it is, the ADM1070 reduces the voltage on the GATE of the FET to reduce the load current to an acceptable level. The load current limit is set by the choice of RSENSE. Table I of the ADM1070 data sheet shows the value of the load current permitted to flow during inrush and quiescent conditions for the different choices of RSENSE.
0V
SHORT CONNECTOR R2
CLOAD
ADM1070
GATE UV/OV SENSE RSENSE VEE Q1
LIVE BACKPLANE R1 * 48V LONG CONNECTOR
TIMER
*OPTIONAL TIMER CAPACITOR
Figure 1. Circuit Diagram (ADM1070 Residing on a Plug-In Module)
REV. A
Analog Devices, Inc., 2002
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