MAX5955BUEE [MAXIM]
Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control;
| 型号： | MAX5955BUEE |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control |
| 文件： | 总15页 (文件大小：360K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-3813; Rev 0; 9/05
Low-Voltage, Dual Hot-Swap
Controllers with Independent On/Off Control
/MAX956
General Description
Features
o Safe Hot Swap for +1V to +13.2V Power Supplies
The MAX5955 and MAX5956 are +1V to +13.2V dual
hot-swap controllers with independent on/off control for
complete protection of dual-supply systems. They allow
the safe insertion and removal of circuit cards into live
backplanes. The MAX5955 and MAX5956 operate
down to 1V provided one of the inputs is above 2.7V.
with V
or V
≥ 2.7V
IN1
IN2
o Independent On/Off Control for Each Channel
o Internal Charge Pumps Generate n-Channel
MOSFET Gate Drives
o Inrush Current Regulated at Startup
o Circuit-Breaker Function
The discharged filter capacitors of the circuit card pro-
vide low impedance to the live backplane. High inrush
currents from the backplane to the circuit card can burn
up connectors and components, or momentarily collapse
the backplane power supply leading to a system reset.
The MAX5955 and MAX5956 hot-swap controllers pre-
vent such problems by gradually ramping up the output
voltage and regulating the current to a preset limit when
the board is plugged in, allowing the system to stabilize
safely. After the startup cycle is completed, two on-chip
comparators provide VariableSpeed/BiLevel™ protection
against short-circuit and overcurrent faults, as well as
immunity against system noise and load transients. In the
event of a fault condition, the load is disconnected. The
MAX5955B and MAX5956B must be unlatched after a
fault, and the MAX5955A and MAX5956A automatically
restart after a fault.
o Adjustable Circuit Breaker/Current-Limit
Threshold from 25mV to 100mV
o VariableSpeed/BiLevel Circuit Breaker Response
o Autoretry or Latched Fault Management
o Status Outputs Indicate Fault/Safe Condition
o Output Undervoltage and Overvoltage Monitoring
or Protection
Ordering Information
PART
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
0°C to +85°C
0°C to +85°C
-40°C to +85°C
-40°C to +85°C
0°C to +85°C
0°C to +85°C
PIN-PACKAGE
16 QSOP
16 QSOP
16 QSOP
16 QSOP
16 QSOP
16 QSOP
16 QSOP
16 QSOP
MAX5955AEEE
MAX5955AEEE+
MAX5955AUEE
MAX5955AUEE+
MAX5955BEEE
MAX5955BEEE+
MAX5955BUEE
MAX5955BUEE+
The MAX5955 and MAX5956 integrate an on-board
charge pump to drive the gates of low-cost, external n-
channel MOSFETs. The devices offer integrated fea-
tures like startup current regulation and current glitch
protection to eliminate external timing resistors and
capacitors. These devices provide open-drain status
outputs, an adjustable startup timer, and adjustable
current limits. The MAX5955 provides output undervolt-
age/overvoltage protection for each channel, while the
MAX5956 provides undervoltage/overvoltage monitor-
ing for each channel.
+Denotes lead-free package.
Ordering Information continued at end of data sheet.
Selector Guide and Typical Operating Circuit appear at end
of data sheet.
The MAX5955 and MAX5956 are available in a space-
saving 16-pin QSOP package.
Pin Configuration
TOP VIEW
Applications
Power-Supply Sequencing
PGOOD1
TIM
1
2
3
4
5
6
7
8
16 PGOOD2
15 ON2
Base Station Line Cards
IN1
14 IN2
Network Switches,
Routers, Hubs
Hot Plug-In Daughter
Cards
SENSE1
GATE1
GND
MAX5955
MAX5956
13 SENSE2
12 GATE2
11 ON1
Solid-State Circuit
Breakers
Portable Computer Device
Bays (Docking Stations)
RAID
LIM1
10 LIM2
MON1
9
MON2
Variable Speed/BiLevel is a trademark of Maxim Integrated
Products, Inc.
QSOP
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
ABSOLUTE MAXIMUM RATINGS
IN_ to GND...........................................................................+14V
Continuous Power Dissipation (T = +70°C)
A
GATE_ to GND ...........................................-0.3V to (V
ON_, PGOOD_, TIM to GND.......................-0.3V to the higher of
+ 6.2V)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
Operating Temperature Range
IN_
(V
+ 0.3V) and (V
+ 0.3V)
+ 0.3V)
MAX59_ _ _U_ _...................................................0°C to +85°C
MAX59_ _ _E_ _................................................-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
IN1
IN2
SENSE_, MON_, LIM_ to GND ...................-0.3V to (V
Current into Any Pin ......................................................... 50mA
IN_
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
= +1V to +13.2V provided at least one supply is higher than +2.7V, V
= V
= +2.7V, T = T
A
to T
, unless otherwise
MAX
IN_
ON1
ON2
MIN
noted. Typical values are at V
= +5V, V
= +3.3V, and T = +25°C.) (Note 1)
IN2 A
IN1
PARAMETER
POWER SUPPLIES
IN_ Input Voltage Range
Supply Current
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
Other V ≥ +2.7V
1.0
13.2
2.3
V
IN
IN
/MAX956
I
I
+ I , V
= +5V, V = +3.3V
IN2
1.2
25
mA
IN
IN1
IN2 IN1
CURRENT CONTROL
T
T
= +25°C
22.5
27.5
27.5
130
A
LIM = GND
= 300kΩ
Slow-Comparator Threshold
V
= -40°C to +85°C
20.5
80
mV
SC,TH
A
(V _ - V
_) (Note 2)
SENSE
IN
R
100
3
LIM
1mV overdrive
10mV overdrive
During startup
ms
µs
Slow-Comparator Response Time
(Note 3)
t
SCD
110
V
2 x V ,
SC TH
SU,TH
FC,TH
Fast-Comparator Threshold
mV
(V _ - V
IN
_)
SENSE
V
V
_ - V
_; normal operation
4 x V
,
SC TH
IN
SENSE
Fast-Comparator Response Time
(V _ - V _)
t
10mV overdrive, from overload condition
_ = V
260
ns
FCD
IN
SENSE
SENSE Input Bias Current
I
V
_
IN
0.03
1
µA
B SENSE
SENSE
MOSFET DRIVER
R
= 100kΩ
6
0.31
4
10.8
0.45
9
16
0.58
17
TIM
Startup Period (Note 4)
Average Gate Current
t
ms
R
TIM
= 4kΩ (minimum value)
START
TIM floating
Charging, V
_ = +5V, V _ = +10V (Note 5)
65
100
130
µA
GATE
IN
I
GATE
Discharging, triggered by a fault or when
3
mA
V
< 0.875V
ON_
V
V
_ = 3V to 13.2V
_ = 2.7V to 3.0V
4.8
4.1
5.4
5.0
6.0
6.0
V
I
- V _,
IN
< 1µA
IN
IN
GATE_
GATE_
Gate-Drive Voltage
ON_ COMPARATOR
ON_ Threshold
V
V
DRIVE
Low to high
Hysteresis
0.85
0.875
25
0.90
V
V
,
ON_ TH
mV
µs
ON_ Propagation Delay
10mV overdrive
50
2
_______________________________________________________________________________________
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
/MAX956
ELECTRICAL CHARACTERISTICS (continued)
(V
= +1V to +13.2V provided at least one supply is higher than +2.7V, V
= V
= +2.7V, T = T
A
to T
, unless otherwise
MAX
IN_
ON1
ON2
MIN
noted. Typical values are at V
= +5V, V
= +3.3V, and T = +25°C.) (Note 1)
IN2 A
IN1
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
0.03
100
MAX
UNITS
µA
V
< 4.5V
> 4.5V
= 4.5V
ON_
ON_
ON_
ON_ Input Bias Current
ON_ Pulse-Width Low
I
V
= V = +13.2V
IN2
V
V
BON
IN1
0.03
1
t
To unlatch after a latched fault
100
µs
UNLATCH
DIGITAL OUTPUT (PGOOD_)
Output Leakage Current
Output Voltage Low
V
_ = 13.2V
1
µA
V
PGOOD
V
I
= 1mA
0.4
OL
SINK
PGOOD_ Delay
t
After t
, MON_ = V
0.75
ms
PGDLY
START
IN_
OUTPUT VOLTAGE MONITORS (MON1, MON2)
Overvoltage
Undervoltage
657
513
687
543
20
707
563
MON_ Trip Threshold
V
mV
MON
MON_ Glitch Filter
µs
MON_ Input Bias Current
V
= 600mV
0.03
µA
MON_
UNDERVOLTAGE LOCKOUT (UVLO)
Startup is initiated when this threshold is
2.10
2.4
2.67
66
V
reached by V
or V , V _ > 0.875V
IN2 ON
UVLO Threshold
V
UVLO
IN1
Hysteresis
100
mV
µs
V
fault
toggled below UVLO to unlatch after a
step from 0 to 2.8V
IN_
IN_
UVLO Glitch Filter Reset Time
100
20
UVLO to Startup Delay
SHUTDOWN LATCH/RESTART
Autoretry Delay
t
V
37.5
ms
D,UVLO
t
Delay time to restart after fault shutdown
64 x t
ms
RETRY
START
Note 1: All devices are 100% tested at T = +25°C and T = +85°C. Limits at T = 0°C and -40°C are guaranteed by design.
A
A
A
Note 2: The MAX5955/MAX5956 slow-comparator threshold is adjustable. V
= R
ꢀ 0.25µA + 25mV (see the Typical
LIM
SC,TH
Operating Characteristics).
Note 3: The current-limit slow-comparator response time is weighted against the amount of overcurrent; the higher the overcurrent
condition, the faster the response time (see the Typical Operating Characteristics).
Note 4: The startup period (t
) is the time during which the slow comparator is ignored and the device acts as a current-limiter
START
by regulating the sense current with the fast comparator (see the Startup Period section).
Note 5: The current available at GATE is a function of V (see the Typical Operating Characteristics).
GATE
_______________________________________________________________________________________
3
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
Typical Operating Characteristics
(Typical Operating Circuits, Q1 = Q2 = Fairchild FDB7090L, V
= +5V, V
= +3.3V, V
= V
= +2.7V, T = +25°C, unless
IN1
IN2
ON1
ON2 A
otherwise noted. Channels 1 and 2 are identical in performance. Where characteristics are interchangeable, channels 1 and 2 are
referred to as X and Y.)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
TOTAL SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT
vs. TEMPERATURE
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
V
= V
= V
= 2.7V
ON2
INY
ON1
V
V
= V
= V
ON1
ON2
IN1
IN2
I
+ I
IN1 IN2
A
B
I
+ I
INX INY
C
I
INX
I
IN1
V
= 5.0V
INY
I
I
INY
IN2
A) V
B) V
C) V
= V
ON2
= V
ON2
= V
ON2
= 3.3V
= 1.5V
= 0
ON1
ON1
ON1
/MAX956
0
2
4
6
8
10
12
14
0
2
4
6
8
10
12
14
-40
-15
10
35
60
85
V
(V)
V
(V)
TEMPERATURE (°C)
INX
INX
GATE CHARGE CURRENT
vs. GATE VOLTAGE
GATE-DRIVE VOLTAGE
vs. INPUT VOLTAGE
GATE CHARGE CURRENT
vs. TEMPERATURE
200
180
160
140
120
100
80
200
180
160
140
120
100
80
6
5
4
3
2
1
0
V
= 2.7V
INY
V
= 13.2V
INX
V
= 5V
INX
V
= 13.2V
INX
V
= 5V
INX
V
= 1V
INX
V
= 1V
INX
60
60
40
40
V
V
= 2.7V
INY
20
20
V
= 2.7V
12
INY
= 0
GATEX
0
0
0
5
10
15
20
0
2
4
6
8
10
14
-40
-15
10
35
60
85
V
(V)
V
(V)
TEMPERATURE (°C)
GATEX
INX
GATE STRONG DISCHARGE CURRENT
vs. GATE VOLTAGE
GATE STRONG DISCHARGE CURRENT
vs. TEMPERATURE
TURN-OFF TIME vs. SENSE VOLTAGE
6
5
4
3
2
1
0
6
5
4
3
2
1
0
10
1
SLOW-COMP. THRESHOLD
FAST-COMP. THRESHOLD
V
= 13.2V
INX
V
= 5V
INX
V
= 13.2V
INX
V
= 5V
INX
0.1
V
V
V
= V
ON2
= 0
ON1
INY
GATEX
= 2.7V
V
= V = 0
ON2
ON1
= V + 6.2V
INX
0.01
0.001
0.0001
V
= 1V
INX
V
= 2.7V
INY
V
= 1V
10
INX
V
= V + 6.2V
GATEX
INX
0
5
10
15
20
-40
-15
35
60
85
0
25 50 75 100 125 150 175 200
- V (mV)
V
(V)
TEMPERATURE (°C)
V
GATEX
IN
SENSE
4
_______________________________________________________________________________________
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
/MAX956
Typical Operating Characteristics (continued)
(Typical Operating Circuits, Q1 = Q2 = Fairchild FDB7090L, V
= +5V, V
= +3.3V, V
= V = +2.7V, T = +25°C, unless
ON2 A
IN1
IN2
ON1
otherwise noted. Channels 1 and 2 are identical in performance. Where characteristics are interchangeable, channels 1 and 2 are
referred to as X and Y.)
SLOW-COMPARATOR THRESHOLD
vs. R
TURN-OFF TIME vs. SENSE VOLTAGE
(EXPANDED SCALE)
STARTUP PERIOD vs. R
TIM
LIM
60
50
40
30
20
10
0
120
100
80
60
40
20
0
10
SLOW-COMP. THRESHOLD
1
0.1
0
100
200
300
(kΩ)
400
500
600
0
100
200
(kΩ)
300
400
20 25 30 35 40 45 50 55 60 65 70 75 80
R
R
TIM
LIM
V
- V
(mV)
SENSE
IN
STARTUP WAVEFORMS
FAST TURN-ON
TURN-OFF TIME
FAST-COMPARATOR FAULT
TURN-OFF TIME
SLOW-COMPARATOR FAULT
MAX5955/56 toc15
MAX5955/56 toc14
MAX5955/56 toc13
V
ON
2V/div
V
V
V
0
0
PGOOD
PGOOD
PGOOD
t
t
0
0
5V/div
FCD
2V/div
SCD
5V/div
I
OUT
125mV STEP
26mV STEP
5A/div
V
- V
IN
SENSE
V
- V
IN
SENSE
100mV/div
100mV/div
V
OUT
5V/div
V
V
GATE
GATE
5V/div
5V/div
V
GATE
0
5V/div
0
1ms/div
= 5.0V, R
400ns/div
= 5.0V
1ms/div
= 5.0V
V
TIM
= 10mΩ,
SENSE
IN
V
IN
V
IN
R
= 27kΩ, C
= 1000µF
BOARD
STARTUP WAVEFORMS
SLOW TURN-ON
AUTORETRY DELAY
MAX5955/56 toc17
MAX5955/56 toc16
V
ON
2V/div
V
GATE
V
PGOOD
5V/div
2V/div
I
OUT
5A/div
V
OUT
5V/div
V
OUT
5V/div
I
OUT
V
GATE
5A/div
5V/div
40ms/div
1ms/div
= 10mΩ, R = 47kΩ,
V
= 5.0V, R
= 10mΩ, R = 47kΩ,
V
= 5.0V, R
SENSE
IN
SENSE TIM
IN
TIM
= 22nF
GATE
C
= 1000µF, R
= 1.4Ω
BOARD
C
= 1000µF, C
BOARD
BOARD
_______________________________________________________________________________________
5
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
Pin Description
PIN
NAME
FUNCTION
Channel 1 Status Output (Open Drain, see the Absolute Maximum Ratings). PGOOD1 asserts high when hot
1
PGOOD1 swap is successful and channel 1 is within regulation. PGOOD1 asserts low during startup, when ON1 is
low, when channel 1 is off, or when channel 1 has any fault condition.
Startup Timer Setting. Connect a resistor from TIM to GND to set the startup period. Leave TIM unconnected
for the default startup period of 9ms.
2
3
4
TIM
IN1
Channel 1 Supply Input. Connect to a supply voltage of 1V to 13.2V.
Channel 1 Current-Sense Input. Connect R
breaker function of channel 1.
from IN1 to SENSE1. Connect to IN1 to disable circuit
SENSE1
SENSE1
5
6
GATE1 Channel 1 Gate-Drive Output. Connect to the gate of an external n-channel MOSFET.
GND
Ground
Channel 1 Current-Limit Setting. Connect a resistor from LIM1 to GND to set the current trip level. Connect to
7
8
LIM1
GND for the default 25mV threshold (see the Slow-Comparator Threshold, R
section).
LIM
Channel 1 Output-Voltage Monitor. Window comparator input. Connect through a resistive divider from
OUT1 to GND to set the channel 1 overvoltage and undervoltage threshold. Connect to IN1 to disable.
/MAX956
MON1
MON2
Channel 2 Output-Voltage Monitor. Window comparator input. Connect through a resistive divider from
OUT2 to GND to set the channel 2 overvoltage and undervoltage threshold. Connect to IN2 to disable.
9
Channel 2 Current-Limit Setting. Connect a resistor from LIM2 to GND to set the current trip level. Connect to
10
LIM2
ON1
GND for the default 25mV threshold (see the Slow-Comparator Threshold, R
section).
LIM
11
12
Channel 1 On/Off Control Input. Channel 1 is turned on when V
> 0.875V.
ON1
GATE2 Channel 2 Gate-Drive Output. Connect to the gate of an external n-channel MOSFET.
Channel 2 Current-Sense Input. Connect R
breaker function of channel 2.
from IN2 to SENSE2. Connect to IN2 to disable circuit-
SENSE2
13
SENSE2
14
15
IN2
Channel 2 Supply Input. Connect to a supply voltage of 1V to 13.2V.
Channel 2 On/Off Control Input. Channel 2 is turned on when V > 0.875V.
ON2
ON2
Channel 2 Status Output (Open Drain, see the Absolute Maximum Ratings). PGOOD2 asserts high when hot
16
PGOOD2
swap is successful and channel 2 is within regulation. PGOOD2 asserts low during startup, when V
low, when channel 2 is off, or when channel 2 has any fault condition.
is
ON2
on-chip comparators. The startup period and current-
limit threshold of the MAX5955/MAX5956 can be
adjusted with external resistors. Figure 1 shows the
MAX5955/MAX5956 functional diagram.
Detailed Description
The MAX5955 and MAX5956 are circuit breaker ICs for
hot-swap applications where a line card is inserted into
a live backplane. The MAX5955 and MAX5956 operate
down to 1V provided one of the inputs is above 2.7V.
Normally, when a line card is plugged into a live back-
plane, the card’s discharged filter capacitors provide
low impedance that can momentarily cause the main
power supply to collapse. The MAX5955 and MAX5956
reside either on the backplane or on the removable
card to provide inrush current limiting and short-circuit
protection. This is achieved by using external n-chan-
nel MOSFETs, external current-sense resistors, and two
The MAX5955/MAX5956 pull both PGOODs low and
both external FETs off for an overcurrent condition. The
MAX5955 also pulls both PGOODs low and both external
FETs off (protection) for an undervoltage/overvoltage
fault, whereas, the MAX5956 ONLY pulls the corre-
sponding fault channel’s PGOOD_ low (monitoring).
When the overvoltage/undervoltage fault disappears on
the MAX5956, the corresponding PGOOD_ automatically
goes high impedance.
6
_______________________________________________________________________________________
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
/MAX956
Figure 1. Functional Diagram
_______________________________________________________________________________________
7
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
MOSFETs. If the fast comparator detects an overcur-
rent, the MAX5955/MAX5956 regulate the gate voltage
to ensure that the voltage across the sense resistor
Startup Period
R
sets the duration of the startup period from 0.45s
TIM
to 50ms (see the Setting the Startup Period, RTIM sec-
tion). The default startup period is fixed at 9ms when
TIM is floating. The startup period begins after the fol-
lowing three conditions are met:
does not exceed V
. This effectively regulates the
SU,TH
inrush current during startup. Figure 2 shows the start-
up waveforms. PGOOD_ goes high impedance 0.75ms
after the startup period if no fault condition is present.
1) V
or V
exceeds the UVLO threshold (2.4V) for
IN2
the UVLO to startup delay (37.5ms).
IN1
VariableSpeed/BiLevel Fault Protection
VariableSpeed/BiLevel fault protection incorporates two
comparators with different thresholds and response
times to monitor the load current (Figure 3). During the
startup period, protection is provided by limiting the
load current. Protection is provided in normal operation
(after the startup period has expired) by discharging
both MOSFET gates with a strong 3mA pulldown cur-
rent in response to a fault condition. After a fault,
PGOOD_ is pulled low, the MAX5955B and MAX5956B
stay latched off and the MAX5955A and MAX5956A
automatically restart.
2) V and V exceed the ON threshold (0.875V).
ON1
ON2
3) The device is not latched or in its autoretry delay (see
the Latched and Autoretry Overcurrent Fault
Management section).
The MAX5955/MAX5956 limit the load current if an
overcurrent fault occurs during startup instead of com-
pletely turning off the external MOSFETs. The slow
comparator is disabled during the startup period and
the load current can be limited in two ways:
/MAX956
1) Slowly enhancing the MOSFETs by limiting the
MOSFET gate-charging current.
Slow-Comparator Startup Period
The slow comparator is disabled during the startup
period while the external MOSFETs are turning on.
Disabling the slow comparator allows the device to
ignore the higher-than-normal inrush current charging
the board capacitors when a card is first plugged into a
live backplane.
2) Limiting the voltage across the external current-
sense resistor.
During the startup period the gate-drive current is limit-
ed to 100µA and decreases with the increase of the
gate voltage (see the Typical Operating Characteris-
tics). This allows the controller to slowly enhance the
ON
PGOOD
SLOW
COMPARATOR
t
+ t
START PGDLY
3ms
V
V
GATE
4.3V TO 5.8V
FAST
COMPARATOR
OUT
V
TH
V
V
GATE
110µs
OUT
V
C
= LARGE
= 0
260ns
SU,TH
BOARD
R
SENSE
C
BOARD
V
SC,TH
V
FC,TH
(4 x V
)
SC,TH
I
LOAD
SENSE VOLTAGE (V - V
)
IN
SENSE
t
ON
Figure 3. VariableSpeed/BiLevel Response
Figure 2. Startup Waveform
8
_______________________________________________________________________________________
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
/MAX956
Slow-Comparator Normal Operation
After the startup period is complete, the slow compara-
tor is enabled and the device enters normal operation.
then automatically restart after the autoretry delay that
is internally set to 64 times t . During the autoretry
START
delay, toggling ON_ below 0.875V does not clear the
fault latch. The autoretry can be overridden, causing
the startup period to begin immediately by toggling one
of the supply voltages below/above the UVLO thresh-
old. When toggling a supply voltage to clear a fault,
remember that the supply voltage must go below and
then above the UVLO threshold for at least 100µs
regardless of the final value of the supply voltage.
The comparator threshold voltage (V
) is adjustable
SC,TH
from 25mV to 100mV. The slow-comparator response
time decreases to a minimum of 100µs with a large
overdrive voltage. Response time is 3ms for a 1mV over-
drive. The variable speed response time allows the
MAX5955/MAX5956 to ignore low-amplitude momentary
glitches, thus increasing system noise immunity. After
an extended overcurrent condition, a fault is generated,
both PGOODs are pulled low and the MOSFET gates
are discharged with a strong 3mA pulldown current.
Output Overvoltage/Undervoltage Fault
Management
The MAX5955/MAX5956 monitor the output voltages with
the MON1 and MON2 window comparator inputs. These
voltage monitors are enabled after the startup period.
Once enabled, the voltage monitor detects a fault if
Fast-Comparator Startup Period
During the startup period, the fast comparator regulates
the gate voltage to ensure that the voltage across the
sense resistor does not exceed the startup fast-com-
V _ is less than 543mV or greater than 687mV.
MON
parator threshold voltage (V
), V
is scaled to
SC,TH
SU,TH
SU,TH
When the MAX5955 protection device detects an output
overvoltage/undervoltage fault on either MON1 or
MON2, both external MOSFET gates are discharged at
3mA and both PGOODs pull low. For the MAX5955A,
the part continuously attempts to restart after each
autoretry period. The part successfully restarts after the
fault is removed and after waiting the autoretry period.
For the MAX5955B, the GATEs are latched off until the
output voltage fault is removed and the fault latch is
cleared by toggling ON_ or by cycling one of the supply
voltages above/below the UVLO threshold.
two times the slow-comparator threshold (V
).
Fast-Comparator Normal Operation
In normal operation, if the load current reaches the fast-
comparator threshold, a fault is generated, both
PGOODs are pulled low, and the MOSFET gates are dis-
charged with a strong 3mA pulldown current. This hap-
pens in the event of a serious current overload or a dead
short. The fast-comparator threshold voltage (V
) is
FC,TH
scaled to four times the slow-comparator threshold
(V ). This comparator has a fast response time of
SC,TH
260ns (Figure 3).
When the MAX5956 monitoring device detects an out-
put overvoltage/undervoltage fault on either MON1 or
MON2, neither external MOSFET gates are affected,
but the PGOOD_ of the channel experiencing the fault
pulls low. Thus the fault is reported on the channel with
the problem, but the MAX5956 does not allow an output
overvoltage/undervoltage fault to disrupt operation by
shutting down the channels. The MAX5956’s PGOOD_
output immediately goes high impedance after the out-
put overvoltage/undervoltage fault is removed.
Undervoltage Lockout (UVLO)
The UVLO prevents the MAX5955/MAX5956 from turning
on the external MOSFETs until one input voltage exceeds
the UVLO threshold (2.4V) for t
. The MAX5955/
D,UVLO
MAX5956 use power from the higher input voltage rail for
the charge pumps. This allows for more efficient charge-
pump operation. The UVLO protects the external
MOSFETs from an insufficient gate-drive voltage. t
D,UVLO
ensures that the board is fully inserted into the backplane
and that the input voltages are stable. Any input voltage
transient on both supplies below the UVLO threshold
The voltage monitors do not react to output glitches of
less than 20µs. A capacitor from MON_ to GND increas-
es the effective glitch filter time. The voltage monitoring
function of the MAX5955/MAX5956 can be disabled by
reinitiates the t
and the startup period.
D,UVLO
connecting V
to MON1 and V
to MON2.
Latched and Autoretry
Overcurrent Fault Management
IN1
IN2
Status Outputs (PGOOD_)
The status output is an open-drain output that pulls low
in response to one of the following conditions:
The MAX5955B/MAX5956B latch the external MOSFETs
off when an overcurrent fault is detected. Toggling ON_
below 0.875V or one of the supply voltages
below/above the UVLO threshold for at least 100µs
clears the fault latch and reinitiates the startup period.
Similarly, the MAX5955A/MAX5956A turn the external
MOSFETs off when an overcurrent fault is detected,
• Overcurrent fault
• Output undervoltage/overvoltage fault
PGOOD_ goes low when the corresponding channel is
forced off (ON_ < 0.875V) (Table 1).
_______________________________________________________________________________________
9
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
Table 1. Status Output Truth Table
OVER/UNDER-
VOLTAGE FAULT
OVER/UNDER-
VOLTAGE FAULT
OVERCURRENT OVERCURRENT
PGOOD1/
PGOOD2
GATE1/
GATE2
PART
FAULT (V
)
FAULT (V
)
OUT1
OUT2
(V
)
(V
)
OUT2
OUT1
Yes
X
X
X
Yes
X
X
Yes
X
X
X
Yes
X
X
X
X
Yes
X
X
X
X
X
X
Yes
X
X
Low/Low
Low/Low
Low/Low
Low/Low
Low/Low
Low/Low
Low/High
High/Low
Off/Off
Off/Off
Off/Off
Off/Off
Off/Off
Off/Off
On/On
On/On
MAX5955
UV/OV
Protection
MAX5956
UV/OV
Monitor
X
X
Yes
No
No
Yes
Sense Resistor
Applications Information
The slow-comparator threshold voltage is adjustable
from 25mV to 100mV. Select a sense resistor that causes
a drop equal to the slow-comparator threshold voltage at
a current level above the maximum normal operating
current. Typically, set the overload current at 1.2 to 1.5
times the full load current. The fast-comparator threshold
is four times the slow-comparator threshold in normal
operating mode. Choose the sense-resistor power rating
Component Selection
/MAX956
n-Channel MOSFET
Select the external MOSFETs according to the applica-
tion’s current levels. Table 2 lists some recommended
components. The MOSFET’s on-resistance (R
)
DS(ON)
should be chosen low enough to have a minimum volt-
age drop at full load to limit the MOSFET power dissi-
to be greater than (I
)2 x V
.
SC,TH
OVERLOAD
pation. High R
causes output ripple if there is a
DS(ON)
pulsating load. Determine the device power rating to
accommodate a short-circuit condition on the board at
startup and when the device is in automatic-retry mode
(see the MOSFET Thermal Considerations section).
Slow-Comparator Threshold, R
LIM
The slow-comparator threshold voltage is adjustable
from 25mV to 100mV, allowing designers to fine-tune
the current-limit threshold for use with standard-value
sense resistors. Low slow-comparator thresholds allow
for increased efficiency by reducing the power dissi-
pated by the sense resistor. Furthermore, the low 25mV
slow-comparator threshold is beneficial when operating
with supply rails down to 1V because it allows a small
percentage of the overall output voltage to be used for
current sensing. The VariableSpeed/BiLevel fault pro-
tection feature offers inherent system immunity against
load transients and noise. This allows the slow-com-
parator threshold to be set close to the maximum nor-
mal operating level without experiencing nuisance
faults. To adjust the slow-comparator threshold, calcu-
Using the MAX5955B/MAX5956B in latched mode allows
the use of MOSFETs with lower power ratings. A MOSFET
typically withstands single-shot pulses with higher dissi-
pation than the specified package rating. Table 3 lists
some recommended manufacturers and components.
Table 2. Recommended n-Channel
MOSFETs
PART NUMBER MANUFACTURER
DESCRIPTION
11mΩ, 8 SO, 30V
22mΩ, 8 SO, 20V
6mΩ, D2PAK, 20V
20mΩ, 8 SO, 30V
30mΩ, 8 SO, 20V
IRF7413
International
Rectifier
IRF7401
late R
as follows:
LIM
IRL3502S
MMSF3300
V
− 25mV
TH
R
=
LIM
Motorola
Fairchild
MMSF5N02H
MTB60N05H
FDS6670A
NDS8426A
FDB8030L
0.25µA
is the desired slow-comparator threshold
2
14mΩ, D PAK, 50V
where V
voltage.
TH
10mΩ, 8 SO, 30V
13.5mΩ, 8 SO, 20V
2
4.5mΩ, D PAK, 30V
10 ______________________________________________________________________________________
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
/MAX956
Table 3. Component Manufacturers
COMPONENT
MANUFACTURER
PHONE
WEBSITE
www.vishay.com
Dale-Vishay
402-564-3131
704-264-8861
888-522-5372
310-233-3331
602-244-3576
Sense Resistors
IRC
www.irctt.com
Fairchild
www.fairchildsemi.com
www.irf.com
MOSFETs
International Rectifier
Motorola
www.mot-sps.com/ppd
Setting the Startup Period, R
START
where:
TIM
The startup period (t
) is adjustable from 0.45ms to
C
is the external gate to ground capacitance
GATE
50ms. The adjustable startup period feature allows sys-
tems to be customized for MOSFET gate capacitance
(Figure 4).
∆V is the change in gate voltage.
GATE
and board capacitance (C ). The startup period is
BOARD
adjusted with the resistance connected from TIM to GND
(R ). R must be between 4kΩ and 500kΩ. The
Q
GATE
is the MOSFET total gate charge.
TIM
TIM
I
is the gate-charging/discharging current.
GATE
startup period has a default value of 9ms when TIM is left
In this case, the inrush current depends on the MOSFET
gate-to-drain capacitance (C ) plus any additional
capacitance from GATE to GND (C
load current (I
floating. Calculate R
with the following equation:
TIM
rss
t
START
=
), and on any
GATE
R
TIM
) present during the startup period.
LOAD
128 × 800pF
where t
is the desired startup period.
START
C
BOARD
I
=
× I
+ I
INRUSH
GATE LOAD
C
+ C
rss
GATE
Startup Sequence
There are two ways of completing the startup sequence.
Case A describes a startup sequence that slowly turns
on the MOSFETs by limiting the gate charge. Case B
uses the current-limiting feature and turns on the
MOSFETs as fast as possible while still preventing a high
Example: Charging and Discharging Times Using
the Fairchild FDB7030L MOSFET
If V
V
= 5V then GATE1 charges up to 10.4V (V
+
IN1
IN1
); therefore ∆V
= 10.4V. The manufacturer’s
DRIVE
GATE
data sheet specifies that the FDB7030L has approxi-
mately 60nC of gate charge and C = 600pF. The
inrush current. The output voltage ramp-up time (t ) is
ON
determined by the longer of the two timings, case A and
rss
MAX5955/MAX5956 have a 100µA gate-charging cur-
rent and a 3mA strong discharging current.
case B. Set the startup timer t
to be longer than t
ON
START
to guarantee enough time for the output voltage to settle.
Case A: Slow Turn-On (Without Current Limit)
There are two ways to turn on the MOSFETs without
reaching the fast-comparator current limit:
R
SENSE
V
OUT
V
IN
C
BOARD
• If the board capacitance (C
inrush current is low.
) is small, the
BOARD
0.1µF
R
PULLUP
• If the gate capacitance is high, the MOSFETs turn
on slowly.
C
GATE
IN_
SENSE
GATE
In both cases, the turn-on time is determined only by the
charge required to enhance the MOSFET. The small
gate-charging current of 100µA effectively limits the out-
put voltage dV/dt. Connecting an external capacitor
between GATE and GND extends turn-on time. The time
required to charge/discharge a MOSFET is as follows:
PGOOD_
MAX5955
MAX5956
ON_
*
GND
C
× ∆V
+ Q
GATE
GATE GATE
* REQUIRED COMPONENTS. SEE THE ON_ COMPARATORS SECTION.
t =
I
GATE
Figure 4. Operating with an External Gate Capacitor
______________________________________________________________________________________ 11
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
C
= 6µF and the load does not draw any current
allows the internal circuits to stabilize after application
of a steeply rising V
BOARD
during the startup period. With no gate capacitor the
inrush current, charge, and discharge times are:
.
IN_
Using the MAX5955/MAX5956 on the
Backplane
6µF
600pF + 0
I
=
×100µA + 0 = 1A
INRUSH
Using the MAX5955/MAX5956 on the backplane allows
multiple cards with different input capacitance to be
inserted into the same slot even if the card does not
have on-board hot-swap protection. The startup period
can be triggered if IN_ is connected to ON_ through a
trace on the card (Figure 5).
0 ×10.4V + 60nC
100µA
t
t
=
= 0.6ms
CHARGE
0 ×10.4V + 60nC
=
= 0.02ms
DISCHARGE
3mA
With a 22nF gate capacitor the inrush current, charge,
and discharge times are:
Input Transients
The voltage at IN1 or IN2 must be above the UVLO dur-
ing inrush and fault conditions. When a short-circuit con-
dition occurs on the board, the fast comparator trips
causing the external MOSFET gates to be discharged at
3mA. The main system power supply must be able to
sustain a temporary fault current, without dropping below
the UVLO threshold of 2.4V, until the external MOSFET is
completely off. If the main system power supply collapses
below UVLO, the MAX5955/MAX5956 force the device to
restart once the supply has recovered. The MOSFET is
turned off in a very short time resulting in a high di/dt. The
backplane delivering the power to the external card must
have low inductance to minimize voltage transients
caused by this high di/dt.
6µF
600pF + 22nF
I
=
×100µA + 0 = 26.5mA
INRUSH
22nF ×10.4V + 60nC
100µA
t
t
=
= 2.89ms
CHARGE
/MAX956
22nF ×10.4V + 60nC
=
= 0.096ms
DISCHARGE
3mA
Case B: Fast Turn-On (with Current Limit)
In applications where the board capacitance (C
)
BOARD
is high, the inrush current causes a voltage drop across
R
that exceeds the startup fast-comparator
SENSE
threshold. The fast comparator regulates the voltage
across the sense resistor to V . This effectively
SU,TH
MOSFET Thermal Considerations
During normal operation, the external MOSFETs dissi-
regulates the inrush current during startup. In this case,
the current charging C can be considered con-
BOARD
pate little power. The MOSFET R
is low when the
DS(ON)
stant and the turn-on time is:
× V ×R
SENSE
MOSFET is fully enhanced. The power dissipated in
2
normal operation is P = I
x R
. The most
DS(ON)
D
LOAD
power dissipation occurs during the turn-on and turn-
off transients when the MOSFETs are in their linear
regions. Take into consideration the worst-case sce-
nario of a continuous short-circuit fault, consider these
two cases:
C
BOARD
IN
t
=
ON
V
SU,TH
The maximum inrush current in this case is:
1) The single turn-on with the device latched after a
fault (MAX5955B/MAX5956B)
V
SU,TH
I
=
INRUSH
R
SENSE
2) The continuous automatic retry after a fault
(MAX5955A/MAX5956A)
Figure 2 shows the waveforms and timing diagrams for a
startup transient with current regulation (see Typical
Operating Characteristics). When operating under this
condition, an external gate capacitor is not required.
ON_ Comparators
The ON_ comparators control the on/off function of the
MAX5955/MAX5956. ON_ allows independent control
over channel 1 and channel 2. Drive ON1 and ON2
high (> 0.875V) to enable channel 1 and channel 2,
respectively. Pull ON_ low (< 0.875V) to disable the
respective channel. An RC time delay must be added
to the ON_ inputs with delay set to at least 20µs. This
MOSFET manufacturers typically include the package
thermal resistance from junction to ambient (R ) and
θJA
θJC
thermal resistance from junction to case (R
), which
determine the startup time and the retry duty cycle
(d = t /t + t ). Calculate the required
START START
RETRY
transient thermal resistance with the following equation:
T
V
− T
A
JMAX
× I
Z
≤
θJA(MAX)
IN START
/ R
SU,TH SENSE
where I
= V
START
12 ______________________________________________________________________________________
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
/MAX956
When the output is short circuited, the voltage drop
across the external MOSFET becomes large. Hence,
the power dissipation across the switch increases, as
does the die temperature. An efficient way to achieve
good power dissipation on a surface-mount package is
to lay out two copper pads directly under the MOSFET
package on both sides of the board. Connect the two
pads to the ground plane through vias, and use
enlarged copper mounting pads on the top side of the
board (refer to the MAX5956 EV Kit data sheet).
Layout Considerations
To take full advantage of the switch response time to an
output fault condition, it is important to keep all traces as
short as possible and to maximize the high-current trace
dimensions to reduce the effect of undesirable parasitic
resistance and inductance. Place the MAX5955/
MAX5956 close to the card’s connector, and a 0.01µF
capacitor to GND should be placed as close as possible
to each V pin. Use a ground plane to minimize imped-
IN
ance and inductance. Minimize the current-sense resis-
tor trace length (< 10mm), and ensure accurate current
sensing with Kelvin connections (Figure 6).
REMOVABLE CARD
WITH NO HOT-INSERTION
PROTECTION
HIGH-CURRENT PATH
BACKPLANE
V
OUT
V
IN
C
BOARD
0.1µF
SENSE RESISTOR
IN_
SENSE_ GATE_
MAX5955
MAX5956
ON_
*
*
*
MAX5955
MAX5956
* REQUIRED COMPONENTS. SEE THE ON_ COMPARATORS SECTION.
Figure 6. Kelvin Connection for the Current-Sense Resistors
Figure 5. Using the MAX5955/MAX5956 on a Backplane
Selector Guide
OUTPUT UNDERVOLTAGE/OVERVOLTAGE
PROTECTION/MONITOR
PART
MAX5955AEEE
FAULT MANAGEMENT
Protection
Protection
Protection
Protection
Monitor
Autoretry
Autoretry
Latched
Latched
Autoretry
Autoretry
Latched
Latched
MAX5955AUEE
MAX5955BEEE
MAX5955BUEE
MAX5956AEEE
MAX5956AUEE
MAX5956BEEE
MAX5956BUEE
Monitor
Monitor
Monitor
______________________________________________________________________________________ 13
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
Typical Operating Circuit
Q1
V
OUT1
V
IN1
0.1µF
*
*
IN1
ON1
SENSE1
GATE1
*
C
ON1
ON2
BOARD1
*
*
ON2
MON1
*
MAX5955
MAX5956
PGOOD1
PGOOD2
GND
PGOOD1
PGOOD2
GND
*
*
MON2
TIM
C
BOARD2
/MAX956
IN2
SENSE2
GATE2
LIM2
LIM1
*
*
*
V
IN2
V
OUT2
Q2
0.1µF
*OPTIONAL
* REQUIRED COMPONENTS. SEE THE ON_ COMPARATORS SECTION.
Ordering Information (continued)
Chip Information
TRANSISTOR COUNT: 3542
PART
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
0°C to +85°C
0°C to +85°C
-40°C to +85°C
-40°C to +85°C
0°C to +85°C
0°C to +85°C
PIN-PACKAGE
16 QSOP
16 QSOP
16 QSOP
16 QSOP
16 QSOP
16 QSOP
16 QSOP
16 QSOP
PROCESS: BiCMOS
MAX5956AEEE
MAX5956AEEE+
MAX5956AUEE
MAX5956AUEE+
MAX5956BEEE
MAX5956BEEE+
MAX5956BUEE
MAX5956BUEE+
+Denotes lead-free package.
14 ______________________________________________________________________________________
Low-Voltage, Dual Hot-Swap Controllers with
Independent On/Off Control
/MAX956
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15
© 2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
Quijano
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