Analog Devices ADM1171 pre Datasheet

2.7V to 16V Hot Swap Controller

Preliminary Technical Data

FEATURES

Allows Safe Board Insertion and Removal from a Live Backplane

Controls Supply Voltages from 2.7 V to 16.5V Adjustable Analog Current Limit with Circuit Breaker Current Sense Output Fast Response Limits Peak Fault Current Automatic Retry or Latch-Off On Current Fault Adjustable Supply Voltage Power-Up Rate Charge Pumped Gate Drive for External N-FET Switch True Soft Start control of Initial Current Profile TIMER pin allows control over timing functions Undervoltage Lockout Adjustable Overvoltage Protection 8-pin TSOT Package

APPLICATIONS

Hot Swap Board Insertion – Line Cards, Raid systems Electronic Circuit Breaker Industrial High Side Switch/Circuit Breaker

APPLICATIONS DIAGRAM

VIN=5V

LONG

with Current Sense Output

ADM1171

GENERAL DESCRIPTION

The ADM1171 is a Hot Swap controller that allows a board to be safely inserted and removed from a live backplane.

An internal charge pumped driver controls the GATE of an external high side N-channel FET for a supply voltage ranging from 2.7V to 16.5V. The ADM1171 provides the initial timing cycle and allows the GATE to be ramped up at an adjustable rate.

The ADM1171 features a fast current limit loop providing active current limiting together with a circuit breaker timer. The magnitude of the current can be determined by the voltage on the CSOUT pin. The signal at the ON pin turns the part on and off and is also used for the reset function.

The SS pin allows the user to control the soft start profile of the current ramp at start-up via an external capacitor. A capacitor connected to the TIMER pin gives the user control over the duty cycle of the PWM retry ratio during current fault.

This part is available in two options: the ADM1171-1 will automatic retry for over-current fault and the ADM1171-2 will latch-off for an over-current fault. The ADM1171 is packaged in an 8-lead TSOT package.

SENSE

OUT

=5V

SHORT

GND

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LONG

ON1

ON2

TIMER

LOAD

SENSE-

GATE

ADM1171

CS_OUT

TIMER

GND

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ADM1171 Preliminary Technical Data

ADM1171—SPECIFICATIONS

Table 1. V

Parameter Min Typ Max Units Conditions

VCC Pin

Operating Voltage Range, VCC 2.7 16.5 V Supply Current, Icc 0.65 1.0 Undervoltage Lockout, V Undervoltage Lockout Hysteresis, V

ON Pin ON Pin Input Current, I On Pin Threshold, VON 1.26 1.3 1.34 ON Pin Threshold Hysteresis, V RS- Pin SENSE Pin Input Current, I Circuit Breaker Limit Voltage, VCB 44 50 56 Fast Current Limit Voltage 60 70 RS- Pin Hot Swap Voltage 2.7 16.5 RS- Pin Input Current, I

Circuit Breaker Limit Voltage, VCB 34 47 60 44 47 53 Over Current Limit Voltage, VOC 40 53 66 50 53 59 GATE Pin GATE Drive Voltage, V GATE Drive Voltage, V GATE Drive Voltage, V

Gate Pullup Current Gate Pulldown Current Gate Pulldown Current Soft Start (SS) Pin

Soft Start Pullup Current 10 Current Setting Gain 20 Soft Start Completion Voltage 1 Pull-Down Current 100 TIMER Pin TIMER Pin Pull-Up Current, I

-48 -60 -72 TIMER Pin Pull-Down Current, I 100 TIMER Pin Threshold High, V TIMER Pin Threshold Low, V

CSOUT Pin

Total Output Voltage Error Gain

Output Impedance

Settling Time

= 2.7V to 16.5V, TA = -40°C to +85°C, Typical Values at TA = 25°C unless otherwise noted.

ON rising

V VCB = (V

V V VCB = (V VCB = (V V V

2.4 2.525 2.65 V VCC Rising

UVLO

UVLOHYS

INON

-100 0 100

ONHYST

INSENSE

10 20 30

µA

INSENSE

TBD -200 TBD

10 20 30

µA

µA mV mV mV mV

GATE

6 8 12 V V

GATE

5 6.5 10 V V

GATE

5 6.5 10 V V

10 12 14 uA V

2 mA V 25 mA V

µA V/V

µA

Vss/Vsense

Fault

-4 -5 -6

TIMERUP

µA

TIMERDN

2 2.5

µA

1.235 1.3 1.365

TIMERH

0.18 0.2 0.22

TIMERL

V V

Initial Cycle, V During Current Fault, V After Current Fault, V Normal Operation, V TIMER rising TIMER falling

-5 0 5 % VCC-SENSE = 100mV

19 20 21 V/V VCC-SENSE = 10 to100mV

KΩ

µs

= VCC

SENSE

– V

SENSE

= VCC, V

SENSE

HOTSWAP

– VCC, VCC = 2.7V

GATE

– VCC, VCC = 5V

GATE

– VCC, VCC = 16.5V

GATE

= 0V

GATE

= 3V, Vcc > UVLO

GATE

= 3V, Vcc < UVLO

GATE

HOTSWAP

= VCC, V

HOTSWAP

– V

SENSE

– V

SENSE

= 0.6 V, Note > 2.2 V

TIMER

)

= 0.6 V, Note > 2.2 V

) ,V

HOTSWAP

) ,V

HOTSWAP

= 1V

TIMER

= 1V

TIMER

= 1V

TIMER

= 0.6 V > 2.2 V

= 1V

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Preliminary Technical Data ADM1171

Absolute Maximum Ratings

Table 2. ADM1171 Absolute Maximum Ratings

Parameter VCC Pin 20V RS- Pins -0.3V to 20V TIMER Pin -0.3V to (VCC + 0.3V) SS Pin TBD ON Pin -0.3V to 20V CSOUT -0.3V to (VCC + 0.3V) GATE Pin VCC + 11V Power Dissipation TBD Storage Temperature –65°C to +125°C Operating Temperature Range –40°C to +85°C Lead Temperature Range

(Soldering 10 sec) Junction Temperature 150°C

Rating

300°C

HOT CIRCUIT INSERTION

When circuit boards are inserted into live backplanes, the supply bypass capacitors can draw large transient currents from the backplane power bus as they charge. Such transient currents can cause permanent damage to connector pins, glitches on the system supply or reset other boards in the system. The ADM1171 is designed to turn a printed circuit board’s supply voltage ON and OFF in a controlled manner, allowing the circuit board to be safely inserted into or removed from a live backplane. The ADM1171 can reside either on the backplane or on the daughter board for hot circuit insertion applications.

OVERVIEW

The ADM1171 is designed to operate over a range of supplies from 2.7V to 16.5V. Upon insertion, an undervoltage lockout circuit determines if sufficient supply voltage is present. When the ON pin goes high an initial timing cycle assures that the board is fully seated in the backplane before the FET is turned on. A single timer capacitor sets the periods for all of the timer functions. After the initial timing cycle the ADM1171 can either start up in current limit or with a lower load current. Once the external FET is fully enhanced and the supply has ramped up, the ADM1171 monitors the load current through an external sense resistor. Overcurrent faults are actively limited to 47mV/R limit. The ADM1171-1 will automatically retry after a current limit fault while the ADM1171-2 latches off. The ADM1171-1 timer function limits the retry duty cycle to 3.8% for FET cooling.

for a specified circuit breaker timer

SENSE

UNDERVOLTAGE LOCKOUT

An internal undervoltage lockout (UVLO) circuit resets the ADM1171 if the V The UVLO has a low-to-high threshold of 2.525V, a 25mV hysteresis. Above 2.525V supply voltage, the ADM1171 will start if the ON pin conditions are met.

supply is too low for normal operation.

ON FUNCTION

The ON pin is the input to a comparator which has a low-tohigh threshold of 1.3V, an 80mV hysteresis and a high-to-

low glitch filter of 30µs and a low-to-high glitch filter of 3us. A

low input on the ON pin resets the ADM1171 TIMER status and turns off the external FET by pulling the GATE pin to ground. A low-to-high transition on the ON pin starts an initial cycle followed by a start-up cycle. A 10k pull-up resistor connecting the ON pin to the supply is recommended. The 10k resistor shunts any potential static charge on the backplane and reduces the overvoltage stress at the ON pin during live insertion. Alternatively, an external resistor divider at the ON pin can be used to program an undervoltage lockout value higher than the internal UVLO circuit. An RC filter can be added at the ON pin to increase the delay time at card insertion if the internal glitch filter delay is insufficient.

GATE FUNCTION

During hot insertion of the PCB, an abrupt application of supply voltage charges the external FET drain/gate capacitance. This can cause an unwanted gate voltage spike. An internal circuit holds GATE low before the internal circuitry wakes up. This reduces the FET current surges substantially at insertion. The GATE pin is held low in reset mode and during the initial

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