Datasheet ADM1176 Datasheet (ANALOG DEVICES)

V

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Hot Swap Controller and

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

2

C® fast mode-compliant interface (400 kHz maximum)

I
Two address pins allow 16 devices on the same bus
10-lead MSOP

APPLICATIONS

Power monitoring/power budgeting
Central office equipment
Telecommunication and data communication equipment
PCs/servers

GENERAL DESCRIPTION

The ADM1176 is an integrated hot swap controller that offers
digital current and voltage monitoring via an on-chip, 12-bit
analog-to-digital converter (ADC), communicated through an

2

I

C interface.

An internal current sense amplifier senses voltage across the sense
resistor in the power path via the VCC pin and the SENSE pin.

I2C® Power Monitor with Convert Pin

ADM1176

FUNCTIONAL BLOCK DIAGRAM

ADM1176

MUX

VCC

SENSE

3.15V TO 16.5

AMPLIFIER

ON

1.3V
UV COMPARATOR

CURRENT

SENSE

V

0

I

R

GND

1

SENSE

SENSEVCC

GATE

SDA

SCL

A

GND

ADM1176

ON

Figure 2. Applications Diagram

12-BIT

ADC

FET DRIVE

CONTROLLER

TIMER

Figure 1.

N-CHANNEL FET

A1TIMER
A0

2

C

I

CONTROLLER

P = VI

SDA
SCL

SDA
SCL
A1
A0

GATE

06046-001

06046-002

The ADM1176 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 ADM1176 protects the external FET by limiting the time
that it spends with maximum current running through 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 once the hot swap event is
complete. In the 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

Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.

A 12-bit ADC can measure the current seen in the sense
resistor, as well as the supply voltage on the VCC pin. An
industry-standard I

2

C interface allows a controller to read
current and voltage data from the ADC. Measurements can be
initiated by an I

2

C command. Alternatively, the ADC can run
continuously, and the user can read the latest conversion data
whenever it is required. Up to 16 unique I

2

C addresses can be

created, depending on the way the A0 and A1 pins are connected.

The ADM1176 is packaged in a 10-lead MSOP.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com
Fax: [phone] ©2006 Analog Devices, Inc. All rights reserved.

ADM1176

TABLE OF CONTENTS

Features.............................................................................................. 1

Initial Timing Cycle ................................................................... 14

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 ........................................................................13

GATE and TIMER Functions During a Hot Swap ................ 14

Calculating Current Limits and Fault Current Limit Time.. 14

Hot Swap Retry on the ADM1176-1 ....................................... 15

Voltage and Current Readback..................................................... 16

Serial Bus Interface..................................................................... 16

Identifying the ADM1176 on the I

General I

Write and Read Operations ...................................................... 18

Quick Command........................................................................ 18

Write Command Byte................................................................ 18

Write Extended Byte .................................................................. 19

Read Voltage and/or Current Data Bytes................................ 20

Applications Waveforms................................................................ 22

Kelvin Sense Resistor Connection ........................................... 23

Outline Dimensions....................................................................... 24

Ordering Guide .......................................................................... 24

2

C Timing.................................................................... 16

2

C Bus............................... 16

REVISION HISTORY

9/06—Revision 0: Initial Version

Rev. 0 | Page 2 of 24

ADM1176

SPECIFICATIONS

VCC = 3.15 V to 16.5 V; TA = −40°C to +85°C; typical values at TA = 25°C, unless otherwise noted.

Table 1.

Parameter Min Typ Max Unit Conditions

VCC PIN

Operating Voltage Range, V
Supply Current, ICC 1.7 2.5 mA
Undervoltage Lockout, V
Undervoltage Lockout Hysteresis, V

ON PIN

Input Current, I

INON

−2 +2 μA
Rising Threshold, V

ONTH

Trip Threshold Hysteresis, V
Glitch Filter Time 3 μs

SENSE PIN

Input Leakage, I

−1 +1 μA V

SENSE

Overcurrent Fault Timing Threshold, V

Overcurrent Limit Threshold, V

Fast Overcurrent Trip Threshold, V

GATE PIN

Drive Voltage, V

3 6 9 V V

GATE

Pull-Up Current 8 12.5 17 μA V
Pull-Down Current 1.5 mA V
5 mA V
7 mA V

TIMER PIN

Pull-Up Current (Power On Reset), I
Pull-Up Current (Fault Mode), I
Pull-Down Current (Retry Mode), I

Pull-Down Current, I
Trip Threshold Hig h, V
Trip Thresho ld Low, V

TIMERDN

TIMERH

TIMERL

A0 PIN, A1 PIN

Set Address to 00, V
Set Address to 01, R

Set Address to 10, I

Set Address to 11, V

ADRLOWV

ADRLOWZ

ADRHIGHZ

ADRHIGHV

Input Current for 11 Decode, I
Input Current for 00 Decode, I

3.15 16.5 V

VCC

2.8 V VCC rising

UVLO

80 mV

UVLOHYST

−100

+100 nA ON < 1.5 V

1.26 1.3 1.34 V ON rising
35 50 65 mV

ONHYST

= V

92 mV

OCTIM

V

SENSE

OCTRIM

= (V

VCC

VCC

TIMER pin

97 100 103 mV

LIM

V

= (V

VCC

− V

LIM

current limit

115 mV

OCFAST

V

OCFAST

= (V

VCC

turned on

− V

VCC

− V

VCC

− V

VCC

= 0 V
= 3 V, V
= 3 V, V
= 3 V, V

, V
, V
, V

TIMERUPPOR

TIMERUPFAULT

TIMERDNRETRY

GATE

9 11 13 V V
7 10 13 V V

GATE

GATE

GATE

GATE

GATE

GATE

−3.5 −5 −6.5 μA Initial cycle, V

−40 −60 −80 μA During current fault, V
2 3 μA

After current fault and during a cool-down
period on a retry device, V

100 μA Normal operation, V

1.26 1.3 1.34 V TIMER rising

0.175 0.2 0.225 V TIMER falling

0 0.8 V Low state

135 150 165 kΩ

Resistor to ground state, load pin with specified
resistance for 01 decode

−1 +1 μA

Open state, maximum load allowed on the A0
pin and the A1 pin for 10 decode

2 5.5 V High state

3 10 μA V

ADRLOW

−40 −22 μA V

ADRHIGH

= 2.0 V to 5.5 V

ADR

= 0 V to 0.8 V

ADR

− V

), fault timing starts on the

SENSE

), closed-loop regulation to a

SENSE

− V

), gate pull-down current

SENSE

= 3.15 V

VCC

= 5 V

VCC

= 16.5 V

VCC

= 3.15 V

VCC

= 5 V

VCC

= 16.5 V

VCC

= 1 V

TIMER

= 1 V

TIMER

= 1 V

TIMER

= 1 V

TIMER

Rev. 0 | Page 3 of 24

ADM1176

Parameter Min Typ Max Unit Conditions

MONITORING ACCURACY

Current Sense Absolute Accuracy −1.45

−1.8

−2.8

−5.7

−1.5

−1.8

−2.95

−6.1

−1.95

−2.45

−3.85

−6.7

V

for ADC Full Scale 105.84 mV

SENSE

Voltage Sense Accuracy −0.85

−0.9 +0.9 %

−0.85

−0.9 +0.9 %

−0.9

−1.15 +1.15 %

VCC for ADC Full Scale,
Low Range (VRANGE = 1)

VCC for ADC Full Scale,
High Range (VRANGE = 0)

I2C TIMING

Low Level Input Voltage, V
High Level Input Voltage, V
Low Level Output Voltage on SDA, V
Output Fall Time on SDA from V

Maximum Width of Spikes Suppressed by
Input Filtering on SDA and SCL Pins

Input Current, II, on SDA/SCL When Not
Driving Out a Logic Low

Input Capacitance on SDA/SCL 5 pF

SCL Clock Frequency, f

Low Period of the SCL Clock 600 ns
High Period of the SCL Clock 1300 ns

1

+1.45 % V

+1.8 % V

+2.8 % V

+5.7 % V

+1.5 % V

+1.8 % V

+2.95 % V

+6.1 % V

+1.95 % V

+2.45 % V

+3.85 % V

+6.7 % V

SENSE

SENSE

SENSE

SENSE

SENSE

SENSE

SENSE

SENSE

SENSE

SENSE

SENSE

SENSE

This is an absolute value to be used when
converting ADC codes to current readings;
any inaccuracy in this value is factored into
absolute current accuracy values (see specs
for Current Sense Absolute Accuracy)

+0.85 %

V

= 3.0 V to 5.5 V

VCC

(low range)

= 10.8 V to 16.5 V

V

VCC

(high range)

+0.85 %

V

= 3.0 V to 5.5 V

VCC

(low range)

= 10.8 V to 16.5 V

V

VCC

(high range)

+0.9 %

V

= 3.0 V to 5.5 V

VCC

(low range)

= 10.8 V to 16.5 V

V

VCC

(high range)

6.65

V

These are absolute values to be used when
converting ADC codes to current readings;

26.52

V

any inaccuracy in these values is factored into
voltage accuracy values (see specs for Current
Sense Absolute Accuracy)

0.3 V

IL

0.7 V

IH

0.4 V I

OL

to V

IHMIN

ILMAX

V

BUS

20 +

0.1 C

250 ns CB = bus capacitance from SDA to GND

B

V

BUS

= 3 mA

OL

50 250 ns

−10 +10 μA

400 kHz

SCL

= 75 mV 0°C to +70°C

= 50 mV 0°C to +70°C

= 25 mV 0°C to +70°C

= 12.5 mV 0°C to +70°C

= 75 mV 0°C to +85°C

= 50 mV 0°C to +85°C

= 25 mV 0°C to +85°C

= 12.5 mV 0°C to +85°C

= 75 mV −40°C to +85°C

= 50 mV −40°C to +85°C

= 25 mV −40°C to +85°C

= 12.5 mV −40°C to +85°C

0°C to +70°C

0°C to +70°C

0°C to +85°C

0°C to +85°C

−40°C to +85°C

−40°C to +85°C

Rev. 0 | Page 4 of 24

ADM1176

Parameter Min Typ Max Unit Conditions

Setup Time for a Repeated Start Condition,
t

SU;STA

SDA Output Data Hold Time, t
Setup Time for a Stop Condition, t

100 900 ns

HD;DAT

600 ns

SU;STO

Bus Free Time Between a Stop and a Start
Condition, t

Capacitive Load for Each Bus Line 400 pF

1

Monitoring accuracy is a measure of the error in a code that is read back for a particular voltage/current. This is a combination of amplifier error, reference error, ADC

error, and error in ADC full-scale code conversion factor.

BUF

600 ns

1300 ns

Rev. 0 | Page 5 of 24

ADM1176

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Rating

VCC Pin 20 V
SENSE Pin 20 V
TIMER Pin −0.3 V to +6 V
ON Pin −0.3 V to +20 V
GATE Pin 30 V
SDA Pin, SCL Pin −0.3 V to +7 V
A0 Pin, A1 Pin −0.3 V to +6 V
Storage Temperature Range −65°C to +125°C
Operating Temperature Range −40°C to +85°C
Lead Temperature (Soldering, 10 sec) 300°C
Junction Temperature 150°C

Table 3. Thermal Resistance

Package Type θJA Unit

10-Lead MSOP 137.5 °C/W

ESD CAUTION

Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.

Rev. 0 | Page 6 of 24

ADM1176

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

1

VCC

SENSE

2

ADM1176

ON

3

TOP VIEW

(Not to Scale)

GND

4
5

TIMER

Figure 3. Pin Configuration

Table 4. Pin Function Descriptions

Pin No. Mnemonic Description

1 VCC

Positive Supply Input Pin. The operating supply voltage range is from 3.15 V to 16.5 V. An undervoltage
lockout (UVLO) circuit resets the ADM1176 when a low supply voltage is detected.

2 SENSE

Current Sense Input Pin. A sense resistor between the VCC pin and the SENSE pin sets the analog current
limit. The hot swap operation of the ADM1176 controls the external FET gate to maintain the (V
voltage at 100 mV or below.

3 ON

Undervoltage Input Pin. Active-high pin. An internal ON comparator has a trip threshold of 1.3 V, and the
output of this comparator is used as an enable for the hot swap operation. With an external resistor divider
from VCC to GND, this pin can be used to enable the hot swap operation on a specific voltage on VCC, giving

an undervoltage function.
4 GND Chip Ground Pin.
5 TIMER

Timer Pin. An external capacitor, C

TIMER

The GATE pin turns off when the TIMER pin is pulled beyond the upper threshold. An overvoltage detection

with an external Zener can be used to force this pin high.
6 SCL I2C Clock Pin. Open-drain input requires an external resistive pull-up.
7 SDA I2C Data I/O Pin. Open-drain input/output. Requires an external resistive pull-up.
8 A0

9 A1

10 GATE

2

C Address Pin. This pin can be tied low, tied high, left floating, or tied low through a resistor. Sixteen different

I

2

I

C address options are available, depending on the external configuration of the A0 pin and A1 pin.

2

C Address Pin. This pin can be tied low, tied high, left floating or tied low through a resistor. Sixteen different

I

2

C address options are available, depending on the external configuration of the A0 pin and the A1 pin.

I

GATE Output Pin. This pin is the high-side gate drive of an external N-channel FET. This pin is driven by the

FET drive controller, which utilizes a charge pump to provide a 12.5 μA pull-up current to charge the FET

GATE pin. The FET drive controller regulates to a maximum load current (100 mV through the sense resistor)

by modulating the GATE pin.

10

GATE
A1

9

A0

8

SDA

7
6

SCL

06046-003

− V

SENSE

)

VCC

, sets a 270 ms/μF initial timing cycle delay and a 21.7 ms/μF fault delay.

Rev. 0 | Page 7 of 24

ADM1176

TYPICAL PERFORMANCE CHARACTERISTICS

2.0

1.8

1.6

1.4

1.2

1.0

(mA)

CC

I

0.8

0.6

0.4

0.2

0

024681014112 16

VCC (V)

Figure 4. Supply Current vs. Supply Voltage

8

06046-021

2.0

1.8

1.6

1.4

1.2

1.0

(mA)

CC

I

0.8

0.6

0.4

0.2

0

–40 806040200–20

TEMPERATURE (°C)

Figure 7. Supply Current vs. Temperature (Gate On)

06046-022

12

10

8

6

DRIVE VOLTAGE (V)

4

2

0

01

Figure 5. Drive Voltage (V

0

–2

–4

–6

(µA)

–8

GATE

I

–10

VCC (V)

− VCC) vs. Supply Voltage

GATE

8161412108642

06046-029

12

10

8

6

DRIVE VOLTAGE ( V)

4

2

0

–40 806040200–20

Figure 8. Drive Voltage (V

0

–2

–4

–6

(µA)

–8

GATE

I

–10

5V V

3.15V V

TEMPERATURE (°C)

− VCC) vs. Temperature

GATE

CC

CC

06046-030

–12

–14

01

VCC (V)

10 12 16148642

8

06046-027

Figure 6. Gate Pull-Up Current vs. Supply Voltage

–12

–14

–40 806040200–20

Figure 9. Gate Pull-Up Current vs. Temperature

Rev. 0 | Page 8 of 24

TEMPERATURE (°C)

06046-028

ADM1176

12

10

8

(mA)

6

GATE

I

4

2

0

01

Figure 10. Gate Pull-Down Current vs. V

VCC (V)

CC

at V

GATE

161412108642

8

06046-031

= 5 V

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

TIMER THRES HO LD (V)

0.4

0.2

0

01810 12 16148642

HIGH

LOW

VCC (V)

06046-038

Figure 13. Timer Threshold vs. Supply Voltage

2

0

–2

–4

(µA)

–6

GATE

I

–8

–10

–12

–14

01

V

GATE

(V)

Figure 11. Gate Pull-Up Current vs. Gate Voltage at V

20

15

(mA)

10

GATE

I

5

VCC = 3V

0

02

V

V

CC

GATE

V

CC

= 5V

(V)

= 12V

1412108642

6

06046-040

= 5 V

CC

2015105

5

06046-043

Figure 12. Gate Pull-Down Current vs. Gate Voltage

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

TIMER HIG H THRESHOLD (V )

0.4

0.2

0

–40 80

Figure 14. Timer Threshold vs. Temperature

100

90

80

70

60

50

40

GATE ON TIME (ms)

30

20

10

0

05.04.54.03.53.02.52.01.51.00.5

Figure 15. Current Limit On Time vs. Timer Capacitance

HIGH

LOW

TEMPERATURE (°C)

C

(µF)

TIMER

6040200–20

06046-039

06046-050

Rev. 0 | Page 9 of 24

ADM1176

0

0

–1

–2

(µA)

–3

TIMER

I

–4

–5

–6

018

VCC (V)

10 12 16148642

06046-032

Figure 16.Timer Pull-Up Current (Initial Cycle) vs. Supply Voltage

0

–10

–20

–30

(µA)

–40

TIMER

I

–50

–60

–1

–2

(µA)

–3

TIMER

I

–4

–5

–6

–40 806040200–20

Figure 19. Timer Pull-Up Current (Initial Cycle) vs. Temperature

0

–10

–20

–30

(µA)

–40

TIMER

I

–50

–60

TEMPERATURE (°C)

06046-033

–70

–80

018

VCC (V)

10 12 16148642

06046-034

Figure 17. Timer Pull-Up Current (C. B. Delay) vs. Supply Voltage

3.0

2.5

2.0

(µA)

1.5

TIMER

I

1.0

0.5

0

01810 12 16148642

VCC (V)

06046-036

Figure 18. Timer Pull-Down Current (Cool-Off Cycle) vs. Supply Voltage

–70

–80

–40 806040200–20

Figure 20. Timer Pull-Up Current (C. B. Delay) vs. Temperature

3.0

2.5

2.0

(µA)

1.5

TIMER

I

1.0

0.5

0

–40 806040200–20

Figure 21. Timer Pull-Down Current (Cool-Off Cycle) vs. Temperature

TEMPERATURE (°C)

TEMPERATURE (°C)

06046-035

06046-037

Rev. 0 | Page 10 of 24

ADM1176

120

115

110

105

(mV)

100

LIM

V

95

90

85

80

21

VCC (V)

8

16141210864

06046-041

Figure 22. Circuit Breaker Limit Voltage vs. Supply Voltage

110

108

106

104

102

100

V (mV)

98

96

94

92

90

–40 806040200–20

Figure 23. V

V

OCFAST

V

LIM

V

OCTIM

TEMPERATURE (°C)

, V

, V

OCTIM

LIM

OCFAST

vs. Temperature

06046-042

1000

900

800

700

600

500

400

300

HITS PER CO DE ( 1000 RE ADS)

200

100

0

2047 2048 2049 20502046

CODE

Figure 25. ADC Noise, Current Channel, Midcode Input, 1000 Reads

1000

900

800

700

600

500

400

300

HITS PER CO DE ( 1000 RE ADS)

200

100

0

780 781 782 783779

CODE

Figure 26. ADC Noise, 14:1 Voltage Channel, 5 V Input, 1000 Reads

06046-060

06046-061

11 DECODE 10 DECODE 0 1 DEC ODE 00 DECODE

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

V (A0/A1)

1.2

1.0

0.8

0.6

0.4

0.2
0

–35 –30 –25 –20 –15 –10 –5 0 5 10

I (A0/A1) (µA)

Figure 24. Address Pin Voltage vs. Address Pin Current

for Four Addressing Options

06046-02606046-026

Rev. 0 | Page 11 of 24

1000

900

800

700

600

500

400

300

HITS PER CO DE ( 1000 RE ADS)

200

100

0

3079 3080 3081 30823078

CODE

Figure 27. ADC Noise, 7:1 Voltage Channel, 5 V Input, 1000 Reads

06046-062

ADM1176

4

4

INL (LSB)

3

2

1

0

–1

–2

–3

–4

0 40002500 3000 3500200015001000500

CODE

Figure 28. INL for ADC

06046-023

DNL (LSB)

3

2

1

0

–1

–2

–3

–4

0 40002500 3000 3500200015001000500

CODE

Figure 29. DNL for ADC

06046-024

Rev. 0 | Page 12 of 24

ADM1176

OVERVIEW OF THE HOT SWAP FUNCTION

When circuit boards are inserted into a live backplane, discharged
supply bypass capacitors draw large transient currents from the
backplane power bus as they charge. Such transient currents can
cause permanent damage to connector pins, as well as dips on
the backplane supply that can reset other boards in the system.
The ADM1176 is designed to turn a circuit board 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
ADM1176 can reside either on the backplane or on the circuit
board itself.

The ADM1176 controls the inrush current to a fixed maximum
level by modulating the gate of an external N-channel FET placed
between the live supply rail and the load. This hot swap function
protects the card connectors and the FET itself from damage and
limits any problems that can be caused by high current loads on
the live supply rail.

The ADM1176 holds the GATE pin down (and, thus, the FET is
held off) until a number of conditions are met. An undervoltage
lockout circuit ensures that the device is provided with an adequate
input supply voltage. Once the input supply voltage has been
successfully detected, the device goes through an initial timing
cycle to provide a delay before it attempts to hot swap. This delay
ensures that the board is fully seated in the backplane before
the board is powered up.

Once the initial timing cycle is complete, the hot swap function
is switched on under control of the ON pin. When the ON pin
is asserted high, the hot swap operation starts.

The ADM1176 charges up the gate of the FET to turn on the
load. It continues to charge up the GATE pin until the linear
current limit (set to 100 mV/R

) is reached. For some combi-

SENSE

nations of low load capacitance and high current limit, this limit
may not be reached before the load is fully charged up. If current
limit is reached, the ADM1176 regulates the GATE pin to keep
the current at this limit. For currents above the overcurrent
fault timing threshold, nominally 100 mV/R

, the current

SENSE

fault is timed by sourcing a current out to the TIMER pin. If the
load becomes fully charged before the fault current limit time is
reached (when the TIMER pin reaches 1.3 V), the current drops
below the overcurrent fault timing threshold. The ADM1176
then charges the GATE pin higher to fully enhance the FET for
lowest R

, and the TIMER pin is pulled down again.

ON

If the fault current limit time is reached before the load drops
below the current limit, a fault has been detected, and the hot
swap operation is aborted by pulling down on the GATE pin to
turn off the FET. The ADM1176-2 latches off at this point and
attempts to hot swap again only when the ON pin is deasserted
and then asserted again.

The ADM1176-1 retries the hot swap operation indefinitely,
keeping the FET in its safe operating area (SOA) by using the
TIMER pin to time a cool-down period in between hot swap
attempts. The current and voltage threshold combinations on
the TIMER pin set the retry duty cycle to 3.8%.

The ADM1176 is designed to operate over a range of supplies
from 3.15 V to 16.5 V.

UNDERVOLTAGE LOCKOUT

An internal undervoltage lockout (UVLO) circuit resets the
ADM1176 if the VCC

supply is too low for normal operation.
The UVLO has a low-to-high threshold of 2.8 V, with 80 mV
hysteresis. Above 2.8 V supply voltage, the ADM1176 starts the
initial timing cycle.

ON FUNCTION

The ADM1176-1 has an active-high ON pin. The ON pin is the
input to a comparator that has a low-to-high threshold of 1.3 V,
a 50 mV hysteresis, and a glitch filter of 3 s. A low input on the
ON pin turns off the hot swap operation by pulling the GATE pin
to ground, turning off the external FET. The TIMER pin is also
reset by turning on a pull-down current on this pin. A low-to­high transition on the ON pin starts the hot swap operation.
A 10 k pull-up resistor connecting the ON pin to the supply
is recommended.

Alternatively, an external resistor divider at the ON pin can be
used to program an undervoltage lockout value higher than the
internal UVLO circuit, thereby setting a voltage level at the
VCC supply where the hot swap operation is to start. An RC
filter can be added at the ON pin to increase the delay time at
card insertion if the initial timing cycle delay is insufficient.

TIMER FUNCTION

The TIMER pin handles several timing functions with an
external capacitor, C
V

(0.2 V) and V

TIMERH

sources are a 5 µA pull-up, a 60 µA pull-up, a 2 µA pull-down,
and a 100 µA pull-down. The 100 µA pull-down is a non-ideal
current source approximating a 7 k resistor below 0.4 V.

. There are two comparator thresholds:

TIMER

(1.3 V). The four timing current

TIMERL

These current and voltage levels, together with the value of C
chosen by the user, determine the initial timing cycle time, the
fault current limit time, and the hot swap retry duty cycle.

Rev. 0 | Page 13 of 24

TIMER

ADM1176

GATE AND TIMER FUNCTIONS DURING
A HOT SWAP

During hot insertion of a board onto a live supply rail at VCC,
the abrupt application of supply voltage charges the external
FET drain/gate capacitance, which 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 also held low during
the initial timing cycle and until the ON pin has been taken
high to start the hot swap operation.

CALCULATING CURRENT LIMITS AND FAULT
CURRENT LIMIT TIME

The nominal linear current limit is determined by a sense
resistor connected between the VCC pin and the SENSE pin
as given by Equation 1.

I

LIMIT(NOM)

The minimum linear fault current is given by Equation 2.

I

LIMIT(MIN)

= V

LIM(NOM)/RSENSE

= V

LIM(MIN)/RSENSE(MAX)

= 100 mV/R

= 90 mV/R

SENSE

SENSE(MAX)

(1)

(2)

During hot swap operation, the GATE pin is first pulled up by
a 12 A current source. If the current through the sense resistor
reaches the overcurrent fault timing threshold, V

OCTIM

, a pull-up
current of 60 µA on the TIMER pin, is turned on; and this pin
starts charging up. At a slightly higher voltage in the sense
resistor, the error amplifier servos the GATE pin to maintain a
constant current to the load by controlling the voltage across
the sense resistor to the linear current limit, V

LIM

.

A normal hot swap is complete when the board supply capaci­tors near full charge and the current through the sense resistor
drops to eventually reach the level of the board load current.
As soon as the current drops below the overcurrent fault timing
threshold, the current into the TIMER pin switches from being a
60 A pull-up to a 100 A pull-down. The ADM1176 then drives
the GATE voltage as high as it can to fully enhance the FET and
reduce R

losses to a minimum.

ON

A hot swap fails if the load current does not drop below the
over-current fault timing threshold, V

, before the TIMER

OCTIM

pin has charged up to 1.3 V. In this case the GATE pin is then
pulled down with a 2 mA current sink. The GATE pull-down
stays on until a hot swap retry starts, which can be forced by
deasserting and then reasserting the ON pin. On the ADM1176-1,
the device retries automatically after a cool-down period.

The ADM1176 also features a method of protection from
sudden load current surges, such as a low impedance fault,
when the current seen across the sense resistor may go well
beyond the linear current limit. If the fast overcurrent trip
threshold, V

, is exceeded, the 2 mA GATE pull-down is

OCFAST

turned on immediately. This pulls the GATE voltage down
quickly to enable the ADM1176 to limit the length of the
current spike that gets through and also to bring the current
through the sense resistor back into linear regulation as quickly
as possible. This process protects the backplane supply from
sustained overcurrent conditions that can otherwise cause the
backplane supply to droop during the overcurrent event.

The maximum linear fault current is given by Equation 3.

I

LIMIT(MAX)

= V

LIM(MAX)/RSENSE(MIN)

= 110 mV/R

SENSE(MIN)

(3)

The power rating of the sense resistor should be rated at the
maximum linear fault current level.

The minimum overcurrent fault timing threshold current is
given by Equation 4.

I

OCTIM(MIN)

= V

OCTIM(MIN)/RSENSE(MAX)

= 85 mV/R

SENSE(MAX)

(4)

The maximum fast overcurrent trip threshold current is given
by Equation 5.

I

OCFAST(MAX)

= V

OCFAST(MAX)/RSENSE(MIN)

= 115 mV/R

SENSE(MIN)

(5)

The fault current limit time is the time that a device spends
timing an overcurrent fault, and is given by Equation 6.

t

FAULT

≈ 21.7 × C

ms/F (6)

TIMER

INITIAL TIMING CYCLE

When VCC is first connected to the backplane supply, the
internal supply (Time Point (1) in
must be charged up. A very short time later (significantly less
than 1 ms), the internal supply is fully up and, because the
undervoltage lockout voltage has been exceeded at VCC, the
device comes out of reset. During this first short reset period,
the GATE pin is held down with a 25 mA pull-down current,
and the TIMER pin is pulled down with a 100 A current sink.

The ADM1176 then goes through an initial timing cycle. At
Time Point (2), the TIMER pin is pulled high with 5 µA. At
Time Point (3), the TIMER reaches the V
the first portion of the initial cycle ends. The 100 µA current
source then pulls down the TIMER pin until it reaches 0.2 V at
Time Point (4). The initial cycle delay (Time Point (2) to Time
Point (4)) is related to C

≈ 270 × C

t

INITIAL

TIMER

ms/F (7)

TIMER

Figure 30) of the ADM1176

threshold, and

TIMERL

by Equation 7.

Rev. 0 | Page 14 of 24

ADM1176

V

When the initial timing cycle terminates, the device is ready to
start a hot swap operation (assuming ON pin is asserted). In the
example shown in
time that V

Figure 30, the ON pin is asserted at the same

is applied, so the hot swap operation starts

CC

immediately after Time Point (4). At this point, the FET gate is
charged up with a 12 A current source.

At Time Point (5), the threshold voltage of the FET is reached,
and the load current begins to flow. The FET is controlled to
keep the sense voltage at 100 mV (this corresponds to a
maximum load current level defined by the value of R

At Time Point (6), V

GATE

and V

have reached their full

OUT

SENSE

).

potential, and the load current has settled to its nominal level.
Figure 31 illustrates the situation where the ON pin is asserted
after V

is applied.

CC

(1)

(2) (3)(4)(5) (6)

V

VCC

V

ON

V

TIMER

V

GATE

SENSE

V

OUT

INITIAL TIMING

CYCLE

Figure 30. Startup (ON Asserts as Power Is Applied)

6046-004

(1) (2) (3)(4) (5)(6) (7)

V

VCC

V

ON

V

TIMER

V

GATE

V

SENSE

V

OUT

INITIAL TIMING

CYCLE

06046-005

Figure 31. Startup (ON Asserts After Power Is Applied)

HOT SWAP RETRY ON THE ADM1176-1

With the ADM1176-1, the device turns off the FET after an
overcurrent fault and then uses the TIMER pin to time a delay
before automatically retrying to hot swap.

As with all ADM1176 devices, on overcurrent fault is timed by
charging the TIMER cap with a 60 A pull-up current. When
the TIMER pin reaches 1.3 V, the fault current limit time has
been reached, and the GATE pin is pulled down. On the
ADM1176-1, the TIMER pin is then pulled down with a 2 A
current sink. When the TIMER pin reaches 0.2 V, it automati­cally restarts the hot swap operation.

The cool-down period is related to C

t

COOL

≈ 550 × C

ms/F (8)

TIMER

Thus, the retry duty cycle is given by Equation 9.

/(t

+ t

t

FAULT

COOL

) × 100% = 3.8% (9)

FAULT

by Equation 8.

TIMER

Rev. 0 | Page 15 of 24

ADM1176

VOLTAGE AND CURRENT READBACK

In addition to providing hot swap functionality, the ADM1176
contains the components to allow voltage and current readback
over an Inter-IC (I

2

C) bus. The voltage output of the current sense
amplifier and the voltage on the VCC pin are fed into a 12-bit
ADC via a multiplexer. The device can be instructed to convert
voltage and/or current at any time during operation via an I

2

C
command. When all conversions are complete, the voltage
and/or current values can be read out to 12-bit accuracy in
two or three bytes.

SERIAL BUS INTERFACE

Control of the ADM1176 is carried out via the I2C bus. This
interface is compatible with fast mode I
The ADM1176 is connected to this bus as a slave device under
the control of a master device.

2

C (400 kHz maximum).

IDENTIFYING THE ADM1176 ON THE I2C BUS

The ADM1176 has a 7-bit serial bus slave address. When the
device powers up, it does so with a default serial bus address.
The three MSBs of the address are set to 100, and the four LSBs
are determined by the state of the A0 pin and the A1 pin. There
are 16 different configurations available on the A0 pin and the
A1 pin that correspond to 16 different I
LSBs (see
to operate on a single I

Table 5. Setting I

A0 Configuration A1 Configuration Address

Low state Low state 0x80
Low state Resistor to GND 0x88
Low state Floating 0x90
Low state High state 0x98
Resistor to GND Low state 0x82
Resistor to GND Resistor to GND 0x8A
Resistor to GND Floating 0x92
Resistor to GND High state 0x9A
Floating Low state 0x84
Floating Resistor to GND 0x8C
Floating Floating 0x94
Floating High state 0x9C
High state Low state 0x86
High state Resistor to GND 0x8E
High state Floating 0x96
High state High state 0x9E

Tabl e 5). This scheme allows sixteen ADM1176 devices

2

C bus.

2

C Addresses via the A0 Pin and the A1 Pin

2

C addresses for the four

GENERAL I2C TIMING

Figure 32 and Figure 33 show timing diagrams for general read
and write operations using the I
conditions for different types of read and write operations, which
are discussed later. The general I

2

C. The I2C specification defines

2

C protocol operates as follows:

1. The master initiates data transfer by establishing a start

condition, defined as a high-to-low transition on the serial
data line, SDA, while the serial clock line SCL remains
high. This indicates that a data stream follows. All slave
peripherals connected to the serial bus respond to the start
condition and shift in the next eight bits, consisting of a 7­bit slave address (MSB first) plus an R/

W

bit that
determines the direction of the data transfer; that is,
whether data is to be written to or read from the slave
device (0 = write, 1 = read).

The peripheral whose address corresponds to the transmitted
address responds by pulling the data line low during the
low period before the ninth clock pulse, known as the
acknowledge bit, and holding it low during the high period of
this clock pulse. All other devices on the bus now remain
idle while the selected device waits for data to be read from
it or written to it. If the R/
slave device. If the R/

W

bit is 0, the master writes to the

W

bit is 1, the master reads from the

slave device.

2. Data is sent over the serial bus in sequences of nine clock

pulses: eight bits of data followed by an acknowledge bit
from the slave device. Data transitions on the data line
must occur during the low period of the clock signal and
remain stable during the high period, because a low-to­high transition when the clock is high can be interpreted as
a stop signal.

If the operation is a write operation, the first data byte after
the slave address is a command byte. This tells the slave
device what to expect next. It can be an instruction, such
as telling the slave device to expect a block write;
or it can be a register address that tells the slave where
subsequent data is to be written.

Because data can flow in only one direction, as defined by

W

the R/

bit, it is not possible to send a command to a slave
device during a read operation. Before doing a read
operation, it may first be necessary to do a write operation
to tell the slave what sort of read operation to expect
and/or the address from which data is to be read.

3. When all data bytes have been read or written, stop

conditions are established. In write mode, the master pulls
the data line high during the 10th clock pulse to assert a
stop condition. In read mode, the master device releases
the SDA line during the low period before the ninth clock
pulse, but the slave device does not pull it low. This is
known as a no acknowledge. The master then takes the data
line low during the low period before the 10th clock pulse,
then high during the 10th clock pulse to assert a stop
condition.

Rev. 0 | Page 16 of 24

ADM1176

SCL

SDA

START BY MAST E R

SCL

(CONTINUED)

SDA

(CONTINUED)

SCL

SDA

START BY MAST E R

SCL

(CONTINUED)

SDA

(CONTINUED)

9

SLAVE

SLAVE

9

SLAVE

MASTER

1

D6

D7

9

2

C Write Timing Diagram

1

D7

9

2

C Read Timing Diagram

D5

1

D6

D5

1

D4

COMMAND CODE

D4

DATA BYTE

D3

FRAME 2

D3

FRAME 2

D2 D1

D2 D1

ACKNOWLEDGE BY

FRAME N

DATA BYTE

ACKNOWLEDGE BY

FRAME N

DATA BYTE

D0

SLAVE

D0

MASTER

1

0

0

11

FRAME 1

SLAVE ADDRESS

1

D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0

A1 A0 R/W

1

FRAME 3

DATA BYTE

ACKNOWLEDG E BY

ACKNOWLEDGE BY

Figure 32. General I

1

0

0

11

FRAME 1

SLAVE ADDRESS

1

D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0

A1 A0 R/W

1

FRAME 3

DATA BYTE

ACKNOWLEDG E BY

ACKNOWLEDGE BY

Figure 33. General I

9

9

ACKNOWLEDG E BY

SLAVE

9

9

NO ACKNOWLEDGE

STOP
BY
MASTER

STOP
BY
MASTER

06046-006

06046-007

t

SU;STA

t

HD;STA

t

SU;STO

P

06046-008

SCLSCL

SDA

t

LOW

t

HD;STA

t

BUF

S

P

t

t

HD;DAT

HIGH

t

F

t

SU;DAT

S

R

t

Figure 34. Serial Bus Timing Diagram

Rev. 0 | Page 17 of 24

ADM1176

WRITE AND READ OPERATIONS

The I2C specification defines several protocols for different
types of read and write operations. The operations used in the
ADM1176 are discussed in the sections that follow.

Tabl e 6

shows the abbreviations used in the command diagrams.

Table 6. I

2

C Abbreviations

Abbreviation Condition

S Start
P Stop
R Read
W Write
A Acknowledge
N No acknowledge

QUICK COMMAND

The quick command operation allows the master to check if the
slave is present on the bus, as follows:

1. The master device asserts a start condition on SDA.

2. The master sends the 7-bit slave address, followed by the

write bit (low).

3. The addressed slave device asserts an acknowledge on SDA.

12 3

SLAVE

S

ADDRESS

Figure 35. Quick Command

Table 7. Command Byte Operations

Bit Default Name Function

C0 0 V_CONT

C1 0 V_ONCE

C2 0 I_CONT

C3 0 I_ONCE

C4 0 VRANGE

C5 0 N/A Unused.
C6 0 STATUS_RD

WA

06046-009

Set to convert voltage continuously. If readback is attempted before the first conversion is complete, the
ADM1176 asserts an acknowledge and returns all 0s in the returned data.

Set to convert voltage once. Self-clears. I
conversion is complete.

Set to convert voltage continuously. If readback is attempted before the first conversion is complete, the
ADM1176 asserts an acknowledge and returns all 0s in the returned data.

Set to convert current once. Self-clears. I
conversion is complete.

Selects different internal attenuation resistor networks for voltage readback. A 0 in C4 selects a 14:1 voltage
divider. A 1 in C4 selects a 7:2 voltage divider. With an ADC full scale of 1.902 V, the voltage at the VCC pin for
an ADC full-scale result is 26.35 V for VRANGE = 0 and 6.65 V for VRANGE = 1.

Status read. When this bit is set, the data byte read back from the ADM1176 is the STATUS byte. This contains
the status of the device alerts. See

Table 15 for full details of the STATUS byte.

WRITE COMMAND BYTE

In the write command byte operation, the master device sends
a command byte to the slave device, as follows:

1. The master device asserts a start condition on SDA.

2. The master sends the 7-bit slave address, followed by the

write bit (low).

3. The addressed slave device asserts an acknowledge on SDA.

4. The master sends the command byte. The command byte

is identified by an MSB = 0. An MSB = 1 indicates an
extended register write (see the

5. The slave asserts an acknowledge on SDA.

6. The master asserts a stop condition on SDA to end the

transaction.

12 3456

SLAVE

S

ADDRESS

Figure 36. Write Command Byte

The seven LSBs of the command byte are used to configure and
control the ADM1176.

Tabl e 7 provides details of the function

of each bit.

2

C asserts a no acknowledge on attempted reads until the ADC

2

C asserts a no acknowledge on attempted reads until the ADC

Write Extended Byte section).

COMMAND

WA

BYTE

AP

06046-010

Rev. 0 | Page 18 of 24

ADM1176

WRITE EXTENDED BYTE

In the write extended byte operation, the master device writes
to one of the three extended registers of the slave device, as
follows:

1. The master device asserts a start condition on SDA.

2. The master sends the 7-bit slave address, followed by the

write bit (low).

3. The addressed slave device asserts an acknowledge on SDA.

4. The master sends the register address byte. The MSB of

this byte is set to 1 to indicate an extended register write.
The two LSBs indicate which of the three extended
registers are to be written to (see

Table 8 ). All other bits

should be set to 0.

5. The slave asserts an acknowledge on SDA.

6. The master sends the command byte. The command byte

is identified by MSB = 0. MSB = 1 indicates an extended
register write.

Table 9. ALERT_EN Register Operations

Bit Default Name Function

0 0 EN_ADC_OC1

Enabled if a single ADC conversion on the I channel has exceeded the threshold set in the ALERT_TH
register.

1 0 EN_ADC_OC4

Enabled if four consecutive ADC conversions on the I channel have exceeded the threshold set in the
ALERT_TH register.

2 1 EN_HS_ALERT

Enabled if the hot swap has either latched off or entered a cool down cycle because of an overcurrent
event.

3 0 EN_OFF_ALERT

Enables an alert if the HS operation is turned off by a transition that deasserts the ON pin or by an
operation that writes the SWOFF bit high.

4 0 CLEAR

Clears the ON_ALERT, HS_ALERT and ADC_ALERT status bits in the STATUS register. These may
immediately reset if the source of the alert has not been cleared or disabled with the other bits in this
register. This bit self-clears to 0 after the STATUS register bits have been cleared.

Table 10. ALERT_TH Register Operations

Bit Default Function

7:0 FF

The ALERT_TH register sets the current level at which an alert occurs. Defaults to ADC full scale. The ALERT_TH 8-bit
number corresponds to the top eight bits of the current channel data.

Table 11. CONTROL Register Operations

Bit Default Name Function

0 0 SWOFF Forces hot swap off. Equivalent to deasserting the ON pin.

7. The slave asserts an acknowledge on SDA.

8. The master asserts a stop condition on SDA to end the

transaction.

12 345678

S

ADDRESS

SLAVE

REGISTER

WA

ADDRESS

Figure 37. Write Extended Byte

REGISTER

A

DATA

AP

06046-011

Tabl e 9 , Ta bl e 10 , and Tabl e 11 give details of each extended
register.

Table 8. Extended Register Addresses

A6 A5 A4 A3 A2 A1 A0 Extended Register

0 0 0 0 0 0 1 ALERT_EN
0 0 0 0 0 1 0 ALERT_TH
0 0 0 0 0 1 1 CONTROL

Rev. 0 | Page 19 of 24

ADM1176

READ VOLTAGE AND/OR CURRENT DATA BYTES

The ADM1176 can be set up to provide information in three
different ways (see the

Write Command Byte section). Depending
on how the device is configured, the following data can be read
out of the device after a conversion (or conversions).

Voltage and Current Readback

The ADM1176 digitizes both voltage and current. Three bytes
are read out of the device in the format shown in

Tabl e 12 .

Table 12. Voltage and Current Readback Format

Byte Contents B7 B6 B5 B4 B3 B2 B1 B0

1

Voltage

V11 V10 V9 V8 V7 V6 V5 V4

MSBs

2

Current

I11 I10 I9 I8 I7 I6 I5 I4

MSBs

3 LSBs V3 V2 V1 V0 I3 I2 I1 I0

Voltage Readback

The ADM1176 digitizes voltage only. Two bytes are read out of
the device in the format shown in

Tabl e 1 3 .

Table 13. Voltage Only Readback Format

Byte Contents B7 B6 B5 B4 B3 B2 B1 B0

1 Voltage MSBs V11 V10 V9 V8 V7 V6 V5 V4
2 Voltage LSBs V3 V2 V1 V0 0 0 0 0

Current Readback

The ADM1176 digitizes current only. Two bytes are read out of
the device in the format shown in

Tabl e 1 4 .

Table 14. Current Only Readback Format

Byte Contents B7 B6 B5 B4 B3 B2 B1 B0

1 Current MSBs I11 I10 I9 I8 I7 I6 I5 I4
2 Current LSBs I3 I2 I1 I0 0 0 0 0

The following series of events occur when the master receives
three bytes (voltage and current data) from the slave device:

For cases where the master is reading voltage only or current
only, only two data bytes are read. Step 7 and Step 8 are not
required.

12 345678910

SLAVE

S

ADDRESS

12 345678

S

RA

DATA 1 DATA 2 NPDATA 3AA

Figure 38. Three-Byte Read from ADM1176

SLAVE

ADDRESS

Figure 39. Two-Byte Read from ADM1176

RA

REGISTER
ADDRESS

REGISTER

A

DATA

NP

06046-012

06046-013

Converting ADC Codes to Voltage and Current Readings

The following equations can be used to convert ADC codes
representing voltage and current from the ADM1175 12-bit
ADC into actual voltage and current values.

Voltage = (V

FULLSCALE

/4096) × Code

where:

V

= 6.65 (7:2 range) or 26.35 (14:1 range).

FULLSCALE

Code is the ADC voltage code read from the device (Bit V0

to V11).

Current = ((I

/4096) × Code)/Sense Resistor

FULLSCALE

where:

FULLSCALE

= 105.84 mV.

I
Code is the ADC current code read from the device (Bit I0

to Bit I11).

Read Status Register

A single register of status data can also be read from the
ADM1176.

1. The master device asserts a start condition on SDA.

2. The master sends the 7-bit slave address, followed by the

read bit (high).

3. The addressed slave device asserts an acknowledge on SDA.

4. The master receives the first data byte.

5. The master asserts an acknowledge on SDA.

6. The master receives the second data byte.

7. The master asserts an acknowledge on SDA.

8. The master receives the third data byte.

9. The master asserts a no acknowledge on SDA.

10. The master asserts a stop condition on SDA, and the

transaction ends.

1. The master device asserts a start condition on SDA.

2. The master sends the 7-bit slave address, followed by the

3. The addressed slave device asserts an acknowledge on SDA.

4. The master receives the status byte.

5. The master asserts an acknowledge on SDA.

Tabl e 1 5 shows the ADM1176 status registers in detail. Note
that Bit 1, Bit 3, and Bit 5 are cleared by writing to Bit 4 of the
ALERT_EN register (CLEAR).

Rev. 0 | Page 20 of 24

read bit (high).

Figure 40. Status Read from ADM1176

12 345

SLAVE

S

ADDRESS

RA

DATA 1 A

06046-014

ADM1176

Table 15. Status Byte Operations

Bit Name Function

0 ADC_OC An ADC-based overcurrent comparison has been detected on the last three conversions
1 ADC_ALERT

2 HS_OC

3 HS_ALERT The hot swap has failed since the last time this was reset. Cleared by writing to Bit 4 of the ALERT_EN register.
4 OFF_STATUS

5 OFF_ALERT An alert has been caused by either the ON pin or the SWOFF bit. Cleared by writing to Bit 4 of the ALERT_EN register.

An ADC-based overcurrent trip has happened, which has caused the alert. Cleared by writing to Bit 4 of the ALERT_EN
register.

The hot swap is off due to an analog overcurrent event. On parts that latch off, this is the same as the HS_ALERT status
bit (if EN_HS_ALERT = 1). On the retry parts, this indicates the current state: a 0 may indicate that the data was read
during a period when the device was retrying, or that it has successfully hot swapped by retrying after at least one
overcurrent timeout.

The state of the ON pin. Set to 1 if the input pin is deasserted. Can also be set to 1 by writing to the SWOFF bit of the
CONTROL register.

Rev. 0 | Page 21 of 24

ADM1176

APPLICATIONS WAVEFORMS

1

2

3

4

CH1 1.5A CH2 1.00V
CH3 20.0V CH4 10.0V

M40.0ms

Figure 41. Inrush Current Control into 220 μF Load

LOAD

, CH2 = V

(CH1 = I

1

2

3

4

TIMER

, CH3 = V

GATE

, CH4 = V

OUT

1

2

3

4

CH1 1.5A CH2 1.00V

06046-070

CH3 20.0V CH4 10.0V

M10.0ms

06046-073

Figure 44. Overcurrent Condition During Operation (ADM1176-1 Model)

)

(CH1 = I

1

2

3

4

LOAD

, CH2 = V

TIMER

, CH3 = V

GATE

, CH4 = V

OUT

)

CH1 1.5A CH2 1.00V
CH3 20.0V CH4 10.0V

M10.0ms

Figure 42. Overcurrent Condition at Startup (ADM1176-1 Model)

(CH1 = I

LOAD

1

2

3

4

CH1 1.5A CH2 1.00V
CH3 20.0V CH4 10.0V

, CH2 = V

TIMER

, CH3 = V

M20.0ms

GATE

, CH4 = V

Figure 43. Overcurrent Condition at Startup (ADM1176-2 Model)

(CH1 = I

LOAD

, CH2 = V

TIMER

, CH3 = V

GATE

, CH4 = V

OUT

OUT

CH1 1.5A CH2 1.00V

06046-071

CH3 20.0V CH4 10.0V

M20.0ms

06046-074

Figure 45. Overcurrent Condition During Operation (ADM1176-2 Model)

)

(CH1 = I

LOAD

, CH2 = V

TIMER

, CH3 = V

GATE

, CH4 = V

OUT

)

06046-072

)

Rev. 0 | Page 22 of 24

ADM1176

KELVIN SENSE RESISTOR CONNECTION

When using a low value sense resistor for high current
measurement, the problem of parasitic series resistance may
arise. The lead resistance can be a substantial fraction of the
rated resistance, making the total resistance a function of lead
length. This problem can be avoided by using a Kelvin sense
connection. This type of connection separates the current path
through the resistor and the voltage drop across the resistor.
Figure 46 shows the correct way to connect the sense resistor
between the VCC pin and the SENSE pin of the ADM1176.

CURRENT
FLOW FROM
SUPPLY

KELVIN SENSE T RACE S

SENSE RESISTOR

VCC SENSE

ADM1176

Figure 46. Kelvin Sense Connections

CURRENT
FLOW TO
LOAD

06046-015

Rev. 0 | Page 23 of 24

ADM1176

OUTLINE DIMENSIONS

3.10

3.00

2.90

6

10

3.10

3.00

2.90

1

PIN 1

0.50 BSC

0.95

0.85

0.75

0.15

0.05

0.33

0.17

COPLANARITY

0.10

COMPLIANT TO JEDEC STANDARDS MO-187-BA

Figure 47. 10-Lead Mini Small Outline Package [MSOP]

ORDERING GUIDE

Model Hot Swap Retry Option Temperature Range Package Description Package Option Branding

ADM1176-1ARMZ-R71 Automatic Retry Version −40°C to +85°C 10-Lead MSOP RM-10 M5U
ADM1176-2ARMZ-R71 Latched Off Version −40°C to +85°C 10-Lead MSOP RM-10 M5V
EVAL-ADM1176EBZ1 Evaluation Board

1

Z = Pb-free part.

5.15

4.90

4.65

5

1.10 MAX

SEATING
PLANE

0.23

0.08

8°
0°

(RM-10)

Dimensions shown in millimeters

0.80

0.60

0.40

Purchase of licensed I2C components of Analog Devices or one of its sublicensed Associated Companies conveys a license for the purchaser under the Philips I2C Patent
Rights to use these components in an I2C system, provided that the system conforms to the I2C Standard Specification as defined by Philips.

©2006 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D06046-0-9/06(0)

Rev. 0 | Page 24 of 24