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Hot Swap Controller and Digital Power Monitor with ALERTB Output ADM1178
FEATURES
Allows safe board insertion and removal from a live backplane Controls supply voltages from 3.15 V to 16.5 V Precision current sense amplifier Precision voltage input 12-bit ADC for current and voltage readback Charge pumped gate drive for external N-channel FET Adjustable analog current limit with circuit breaker ±3% accurate hot swap current limit level Fast response limits peak fault current Automatic retry or latch-off on current fault Programmable hot swap timing via TIMER pin Active-high ON pin ALERTB output for overcurrent interrupt I2C® fast mode-compliant interface (400 kHz maximum) 10-lead MSOP
FUNCTIONAL BLOCK DIAGRAM
ADM1178
MUX VCC V 0 12-BIT ADC 1 SDA I2 C SCL ADR CURRENT SENSE AMPLIFIER
I A SENSE
ALERT
ALERTB
ON 1.3V
FET DRIVE CONTROLLER
GATE
GND
TIMER
Figure 1.
APPLICATIONS
Power monitoring/power budgeting Central office equipment Telecommunication and data communication equipment PCs/servers
3.15V TO 16.5V
RSENSE
N-CHANNEL FET
VCC
SENSE GATE
CONTROLLER P = VI
SDA SCL INTERRUPT
ADM1178
GENERAL DESCRIPTION
The ADM1178 is an integrated hot swap controller and current sense amplifier that offers digital current and voltage monitoring via an on-chip, 12-bit analog-to-digital converter (ADC), communicated through an I2C interface. An internal current sense amplifier senses voltage across the sense resistor in the power path via the VCC pin and the SENSE pin. The ADM1178 limits the current through this resistor by controlling the gate voltage of an external N-channel FET in the power path, via the GATE pin. The sense voltage (and, therefore, the inrush current) is kept below a preset maximum. The ADM1178 protects the external FET by limiting the time that it spends with the maximum current running in it. This current limit period is set by the choice of capacitor attached to the TIMER pin. Additionally, the device provides protection from overcurrent events that may occur after the hot swap event is complete. In case of a short-circuit event, the current in the sense resistor exceeds an overcurrent trip threshold, and the FET is switched off immediately by pulling down the GATE pin.
Rev. 0
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ON
SDA SCL ALERTB
TIMER
06048-002
GND
ADR
Figure 2. Applications Diagram
A 12-bit ADC can measure the current seen in the sense resistor, as well as the supply voltage on the VCC pin. An alert output can be set to trigger when the ADC current reading exceeds a programmed overcurrent limit threshold. An industry-standard I2C interface allows a controller to read current and voltage data from the ADC. Measurements can be initiated by an I2C command. Alternatively, the ADC can run continuously, and the user can read the latest conversion data whenever it is required. Up to four unique I2C addresses can be created, depending on the way the ADR pin is connected. The ADM1178 is packaged in a 10-lead MSOP.
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ADM1178 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 6 ESD Caution.................................................................................. 6 Pin Configuration and Function Descriptions............................. 7 Typical Performance Characteristics ............................................. 8 Overview of the Hot Swap Function............................................ 13 Undervoltage Lockout ............................................................... 13 ON Function ............................................................................... 13 TIMER Function ..................................................................