LM5068
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SNVS254C – JANUARY 2004 – REVISED MARCH 2013
LM5068 Negative Voltage Hot Swap Controller
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FEATURES
DESCRIPTION
•
The LM5068 hot-swap controller provides intelligent
control of power supply connections during the
insertion and removal of circuit cards powered by live
system backplanes.
1
2
•
•
•
•
•
•
•
•
•
Safe Module Insertion and Removal from Live
Backplanes
In-Rush Current Limiting for Safe Board
Insertion into Live Backplanes
Fast Response to Over-Current Fault
Conditions with Active Current Limiting
-10V to -90V Input Range
Programmable Under-Voltage/Over-Voltage
Shutdown Protection with Adjustable
Hysteresis
Programmable Multi-Function Timer for Board
Insertion De-Bounce Delay
Fault Timer Avoids Nuisance Trips Caused by
Short Duration Load Transients
Active Gate Clamping During Initial Power
Application
Available in both Latched Fault and Automatic
Re-Try Versions
Available with either Active HIGH or Active
LOW Power Good Flag
APPLICATIONS
•
•
•
•
•
•
The LM5068 provides both in-rush current control and
short-circuit protection functions, and limits power
supply transients in the backplane caused by the
insertion of additional circuit cards. The LM5068
controls the external N-Channel MOSFET to provide
programmable load current limiting and circuit
breaker functions using a single external current
sense resistor. The LM5068 issues a power good
(PWRGD) signal at the conclusion of a successful
power-on sequence. Input over-voltage or under voltage fault conditions will cancel the PWRGD
indication.
The LM5068-1 and -2 indicate power-good as an
open-drain active HIGH PWRGD state. The LM50683 and -4 indicate power-good as an open-drain active
LOW PWRGD state. The LM5068-1 and -3 latch off
after a fault condition is detected while the LM5068-2
and -4 continuously re-try at intervals set by a
programmable timer.
The LM5068 is available in a VSSOP-8 package.
- 48V Power Modules
Central Office Switching
Distributed Power Systems
Electronic Circuit Breaker
PBX Systems
Negative Power Supply Control
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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LM5068
SNVS254C – JANUARY 2004 – REVISED MARCH 2013
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Typical Application
VDD (GND)
RF
499:
ENABLE
R1
100 k:
1%
CF
+ 0.1 PF
+
PWRGD
VDD
CL
100 PF
UV
R2
5.5 k:
1%
LOAD
LM5068
OV
VEE
TIMER
R3
4.5 k:
1%
CT
0.22 PF
Cc
22 nF
Rs
12 m:
VEE (-48V)
GATE
+
+
SENSE
Q1
SUB85N10-10
Figure 1. Negative Power Supply Control
Connection Diagram
1
8
VDD
PWRGD
2
7
TIMER
OV
LM5068
3
6
UV
GATE
VEE
SENSE
4
2
5
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PIN DESCRIPTION
PIN
NAME
1
PWRGD
2
3
DESCRIPTION
APPLICATION INFORMATION
Open Drain Power Good indicator
Following a successful power-up sequence the PWRGD
signal will be active. The LM5068-1 and -2 are configured
for an active power-good state as HIGH, while the
LM5068-3 and –4 are configured for an active power-good
state as LOW.
OV
Line Over-Voltage Shutdown
An external resistor divider from the power source sets the
over-voltage shutdown level. Hysteresis is generated by an
internal current source which sources 20 µA into the
external divider when the OV pin exceeds 2.5V.
UV
Line Under-Voltage Shutdown
An external resistor divider from the power source sets the
under-voltage shutdown level. Hysteresis is set by an
internal current source which sinks 20 µA from the external
divider when the UV pin falls below 2.5V.
4
VEE
Negative Supply Voltage Input
5
SENSE
6
Current Sense Input
Load current is monitored via an external current sense
resistor (Rs). If the voltage across Rs exceeds 50mV the
fault timer is initiated. Load current is actively limited to
100mV/Rs. If the sense voltage exceeds 200mV due to a
catastrophic fault, the fast gate pull down circuit will reduce
the MOSFET gate voltage and initiate active current
limiting.
GATE
N-Channel MOSFET Gate Drive Output
This output is pulled high by a 60 µA current source to turn
on the MOSFET.
7
TIMER
Timer Input
An external capacitor connected to this pin sets the initial
start-up delay and the delay to shutdown in the event of an
over-current condition. This pin is also used for the
automatic re-try timing sequence, following fault shutdown
(-2 and –4 versions).
8
VDD
Positive Supply Voltage Input
Configuration Table
Part Number
Latch Off /Successive Re-try
Power Good Polarity
LM5068MM-1/MMX-1
Latch Off
Active HIGH
LM5068MM-2/MMX-2
Auto Re-try
Active HIGH
LM5068MM-3/MMX-3
Latch Off
Active LOW
LM5068MM-4/MMX-4
Auto Re-try
Active LOW
Package
VSSOP- 8
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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SNVS254C – JANUARY 2004 – REVISED MARCH 2013
Absolute Maximum Ratings
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(1) (2)
VDD (VDD to VEE)
100V
PWRGD (PWRGD to VEE)
100V
SENSE (SENSE to VEE)
8V
UV/OV (Clamped) (UV/OV to VEE)
8V
All Other Inputs to VEE
16V
Junction Temperature (TJ)
+150°C
Storage Temperature (TS)
-55°C to +150°C
Soldering Information
ESD Rating
(1)
(2)
(3)
(3)
2kV
Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which
operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
The ESD rating of Pin 7 is 1.5kV. It is recommended that proper ESD precautions are taken to avoid performance degradation or loss of
functionality.
Operating Ratings
Supply Voltage Range (VDD)
10V to 90V
Junction Temp. Range
−40°C to +105°C
Electrical Characteristics
Specifications in standard typeface are for TJ = +25°C, and those in boldface type apply over the full operating junction
temperature range. Unless otherwise noted VDD − VEE = 48V.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
0.82
1.3
mA
580
1000
µA
90
V
VDD Supply
IIN
Supply Current
ISD
Shutdown Current
VDD − VEE
Operating Supply Range
UV/OV = 0V
10
UV/OV Shutdown
VUVS
VDD Under-voltage Shutdown
8.5
V
VUVSH
VDD Under-voltage Shutdown
Hysteresis
0.6
V
VUV
Under-voltage Comparator
Threshold
IUVHCS
Under-voltage Hysteresis Current
Source
VOV
Over-voltage Comparator
Threshold
IOVHCS
Over-voltage Hysteresis Current
Sink
tUVCD
UV Comparator Delay
UV Low to Gate Low
1100
ns
tOVCD
OV Comparator Delay
OV High to Gate Low
500
ns
2.45
2.5
2.55
V
18
20
22
µA
2.45
2.5
2.55
V
18
20
22
µA
Current Limit Voltage
VCB
Circuit Breaker Current Limit
Voltage
40
50
60
mV
VAC
Analog Current Limit Voltage
80
100
120
mV
VFDC
Fast Discharge Current Limit
Voltage (Fast Gate Pull Down
Threshold)
150
200
250
mV
-30
-15
Sense Input
ISENSE
4
Sense Input Current
VSENSE = 50mV
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µA
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Electrical Characteristics (continued)
Specifications in standard typeface are for TJ = +25°C, and those in boldface type apply over the full operating junction
temperature range. Unless otherwise noted VDD − VEE = 48V.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Timer
VTHVT
Timer High Voltage Threshold
4
VTLVT
Timer Low Voltage Threshold
1
ITIMER
Timer On (Initial Cycle, Sourcing)
VTIMER = 2V
Timer Off (Initial Cycle, Sinking)
VTIMER = 2V
Timer On (Circuit Breaker,
Sourcing)
VTIMER = 2V
200
240
280
µA
Timer Off (Cooling Cycle, Sinking)
VTIMER = 2V
4
6
8
µA
Saturation Gate Drive Voltage
VDD- VEE = 48V
9
10.6
12
V
4
6
V
V
8
27
µA
mA
Gate Drive
VG
VDD- VEE = 10V
7.8
V
VGLT
Gate Low Threshold
Before Gate ramp-up
IGATE
Gate Pin Current (Sourcing)
VSENSE = 0V
0.5
Gate Pin Current (Sinking)
VSENSE = 150mV
VGATE = 3V
2.7
mA
Gate Pin Current (Sinking)
VSENSE = 300mV
VGATE = 1V
300
mA
VPGLV
PWRGD Low Voltage
ISINK = 1mA
0.2
IPGLC
PWRGD High Leakage Current
VPWRGD = 90V
VPGV
GATE Voltage at onset of PWRGD
40
60
V
80
µA
PWRGD
0.6
V
1
µA
8
V
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Block Diagram
VREG
+
SERIES
REGULATOR
VDD
UV HYSTERESIS CS
0.5V
20PA
2.5V
+
-
UV
60PA
OV
+
2.5V
GATE
20PA
OV HYSTERESIS CS
VREG
CONTROL
LOGIC
+
200mV
UV/OV
or
FAULT
VEE
VEE
VREG
6PA
240PA
+
4V
100mV
+
-
+
-
TIMER
VEE
200Ps
SOFTSTART
1V
+
-
SENSE
50mV
6PA
VEE
PWRGD / PWRGD
VEE
VEE
6
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VEE
VEE
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Typical Performance Characteristics
IIN
vs
Temperature
IIN
vs
VDD
1.2
0.801
VDD = 90V
-40oC
0.701
1.1
0.601
1
-25oC
IIN (mA)
IIN (mA)
0.501
0.9
VDD = 48V
125oC
0.401
0.301
0.8
0.201
0.7
0.101
0.6
-40
0.001
-25
0
25
50
75
105
0
2
4
6
8
VDD (V)
TEMPERATURE (oC)
Figure 2.
Figure 3.
VDD Under-Voltage Shutdown (VUVS)
vs
Temperature
VDD Under-Voltage Shutdown Hysteresis (VUVSH)
vs
Temperature
8.6
0.8
8.55
0.75
8.5
0.7
8.45
0.65
VUVSH (V)
VUVS (V)
10 12 14 16 18 20 22
8.4
8.35
0.6
0.55
8.3
0.5
8.25
0.45
8.2
-40
-25
0
50
25
75
0.4
-40
105
-25
0
25
50
75
105
TEMPERATURE (oC)
TEMPERATURE (oC)
Figure 4.
Figure 5.
Under-Voltage Comparator Threshold (VUV) and OverVoltage Comparator Threshold (VOV)
vs
Temperature
Under-Voltage Comparator Threshold Hysteresis Current
Source (IUVHCS)
vs
Temperature
2.52
21
VOV
2.50
20.5
IUVHCS (PA)
VUV(V) / VOV(V)
2.51
21.5
VUV
2.49
20
2.48
19.5
2.47
19
2.46
-40
-25
0
25
50
75
105
18.5
-40
-25
0
25
50
TEMPERATURE (oC)
TEMPERATURE (oC)
Figure 6.
Figure 7.
75
105
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Typical Performance Characteristics (continued)
Over-Voltage Comparator Threshold Hysteresis Current
Sink (IOVHCS)
vs
Temperature
1400
21
1200
tUVCD (ns) / tOVCD(ns)
21.5
20.5
IOVHCS (PA)
UV Comparator Delay (tUVCD) and OV Comparator Delay
(tOVCD)
vs
Temperature
20
19.5
tUVCD
1000
800
600
tOVCD
19
18.5
-40
400
-25
0
25
50
75
200
-40
105
-25
0
25
50
75
105
TEMPERATURE (oC)
TEMPERATURE (oC)
Figure 8.
Figure 9.
Circuit Breaker Current Limit Voltage (VCB)
vs
Temperature
Analog Current Limit Voltage (VAC)
vs
Temperature
55
106
104
53
VAC (mV)
VCB (mV)
102
51
100
98
49
96
47
-40
-25
0
25
50
75
94
-40
105
-25
o
25
50
75
105
o
TEMPERATURE ( C)
Figure 10.
Figure 11.
Fast Discharge Current Limit Voltage (VFDC)
vs
Temperature
Timer High Voltage Threshold (VTHVT)
vs
Temperature
215
4.3
210
4.2
205
4.1
VTHVT (V)
VFDC (mV)
TEMPERATURE ( C)
200
4.0
195
3.9
190
3.8
185
-40
-25
0
25
50
75
105
o
8
0
3.7
-40
-25
0
25
50
75
105
o
TEMPERATURE ( C)
TEMPERATURE ( C)
Figure 12.
Figure 13.
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Typical Performance Characteristics (continued)
Timer On (Initial Cycle, Sourcing)
vs
Temperature
1.2
7.5
1.16
7.0
1.12
6.5
ITIMER (PA)
VTLVT (V)
Timer Low Voltage Threshold (VTLVT)
vs
Temperature
1.08
6.0
1.04
5.5
1.0
5.0
0.96
-40
-25
0
25
50
75
4.5
-40
105
-25
0
25
50
75
105
o
TEMPERATURE ( C)
TEMPERATURE ( C)
Figure 14.
Figure 15.
Timer On (Circuit Breaker, Sourcing)
vs
Temperature
Timer Off (Cooling Cycle, Sinking)
vs
Temperature
260
7.5
250
7
240
6.5
ITIMER (PA)
ITIMER (PA)
o
230
6
220
5.5
210
5
200
-40
-25
0
25
50
75
4.5
-40
105
-25
0
o
25
50
75
105
o
TEMPERATURE ( C)
TEMPERATURE ( C)
Figure 16.
Figure 17.
Saturation Gate Drive Voltage (VG)
vs
Temperature (48V)
Saturation Gate Drive Voltage (VG)
vs
Temperature
8
12
11.5
7.95
VDD - VEE = 48V
VDD - VEE = 10V
7.9
11
VG (V)
VG (V)
7.85
10.5
7.8
7.75
10
7.7
9.5
9
-40
7.65
-25
0
25
50
75
105
7.6
-40
-25
0
25
50
75
105
TEMPERATURE (oC)
TEMPERATURE (oC)
Figure 18.
Figure 19.
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Typical Performance Characteristics (continued)
PWRGD Low Voltage (VPGLV)
vs
Temperature
75
0.35
70
0.3
65
0.25
VPGLV (V)
IGATE (PA)
Gate Pin Current (Sourcing) (IGATE)
vs
Temperature
60
0.2
55
0.15
50
0.1
45
-40
-25
0
25
50
75
ISINK = 1mA
0.05
-40
105
25
0
25
50
TEMPERATURE ( C)
TEMPERATURE (oC)
Figure 20.
Figure 21.
o
75
105
Gate Voltage at onset of PWRGD (VPGV)
vs
Temperature
8.1
8.05
8.0
VPGV (V)
7.95
7.9
7.85
7.8
7.75
7.7
-40
-25
0
25
50
75
105
TEMPERATURE (oC)
Figure 22.
10
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FUNCTION DESCRIPTION
The LM5068 is designed to facilitate the insertion and removal of circuit cards into live backplanes in a controlled
manner. Because the supply bypass capacitors on the circuit card can draw large transient currents, it is critical
to control the supply current during insertion to limit system power glitches and connector damage. Controlling inrush current prevents other boards in the system from resetting during board insertion. Load short-circuit
protection is accomplished by active current limiting of the load current. The topology of the LM5068 is illustrated
in the simplified application circuit shown in Figure 23.
PLUG-IN BOARD
+
LIVE
BACKPLANE
CL
LM5068
DC-DC
CONVERTER
VDD (GND)
VEE (-48V)
Figure 23. LM5068 Topology
Start-Up Operation
The LM5068 resides on a removable circuit card. Power is applied to the load or power conversion circuitry
through an external N-Channel MOSFET switch and current sense resistor.
When power is initially applied to the card, the gate of the external MOSFET is held low. When certain interlock
conditions are met, a turn-on sequence begins and an internal 60 µA current source charges the gate of the
MOSFET. To initiate the start-up sequence, all of the following interlock conditions must be satisfied:
• The input voltage VDD - VEE exceeds 9V(VUVS)
• The voltage at UV is above 2.5V (VUV)
• The voltage at OV falls below 2.5V (VOV)
• The voltage on the Timer capacitor (CT) is less than 1V (VTLVT)
• The GATE pin is below 0.5V (VGLT)
When all of the interlock conditions are met, a 6 µA TIMER current source is enabled to charge the timer
capacitor CT. During this initial timer sequence the GATE output is held low. When the CT capacitor successfully
charges up to 4V, the TIMER circuit resets the timer capacitor to 1V and activates a 60 µA current source (IGATE)
into the MOSFET gate.
VDD
(GND)
RF
R1
+C
F
VDD
PWRGD
CL
UV
+
LM5068
R2
OV
TIMER
R3
+C
VEE
SENSE GATE
T
+
CC
VEE
(-48V)
RS
Q1
Figure 24. Hot Swap Controller
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Over and Under-Voltage Lockout
The line Under-voltage lockout (UVLO) circuitry of the LM5068 monitors VDD for under-voltage conditions, where
VUVS is the negative going threshold and the hysteresis is VUVSH (see Electrical Characteristics). A VDD - VEE
voltage less than 8.5V (VUVS) keeps the controller in a disabled mode. Raising the VDD voltage above 9.1V (VUVS
+ VUVSH) releases the VDD UVLO and enables the controller.
In addition to the internal UVLO circuit, the UV and OV comparators monitor the input line voltage through an
external resistor divider. Programmable UV and OV comparator hysteresis is implemented with switched 20µA
current sources that raise or lower the OV and UV pins when the comparators reach their threshold. Either UV or
OV fault conditions will switch the GATE pin low and disconnect the power to the load. To restart the GATE pin,
the supply voltage must return to a level which is greater than the UV fault and less than the OV fault threshold
and all of the interlock conditions (with the exception of the TIMER) must be met.
Removal of the circuit card from the backplane initiates an under-voltage condition. The series MOSFET is then
disabled to disconnect the source of power to the load. The under-voltage threshold and hysteresis are
programmed by the external resistor divider connected to the UV pin.
Timer
The value of the CT capacitor sets the duration of the LM5068’s timer delay and filter functions. There are four
charging and discharging modes:
1. 6µA slow charge for initial timing delay and post-fault re-try timer (LM5068-2 and -4)
2. 240µA fast charge for circuit breaker delay.
3. 6µA slow discharge for circuit breaker "cool-off".
4. Low impedance switch to reset capacitor after initial timing delay, input under-voltage lockout, and during
over-voltage and under-voltage initial timing.
Current Control
The LM5068 has three current sense thresholds which protect the backplane supply and circuit card from
overload conditions. The voltage drop across the sense resistor (RS) is monitored at the SENSE pin. The overcurrent protection functions are determined through the following three distinct thresholds at the SENSE pin:
1. Circuit Breaker (CB) threshold (typically 50mV)
2. Analog Current Limit (ACL) loop threshold (typically 100mV)
3. Fast Discharge Current (FDC) threshold (typically 200mV)
When the voltage drop across RS exceeds 50mV the Circuit Breaker comparator indicates an over-load
condition. The TIMER sources 240µA into CT when SENSE exceeds 50mV and sinks 6µA from CT when SENSE
falls below 50mV. If the CT capacitor ramps to a 4V threshold, a fault condition is declared and the gate of the
MOSFET is forced low, disconnecting the power to the load.
Active Current Limiting (ACL) is activated when the voltage across sense resistor RS reaches 100mV. The
LM5068 controls the gate of the MOSFET and maintains a constant output load current equal to 100mV/ RS. In
the ACL mode the SENSE pin is greater than 50mV and the TIMER charges CT with 240µA. A fault will be
declared if the LM5068 remains in the ACL mode longer than the circuit breaker timer period.
Fast Discharge Current (FDC) responds to fast rising over-loads such as short circuit faults. During a short circuit
event the fast rising current may overshoot past the ACL threshold due to the finite response time of the ACL
loop. If the SENSE voltage reaches 200mV a fast discharge comparator quickly pulls GATE pin low. The rapid
response of the FDC circuit assures a fast and safe transition to the ACL mode.
The LM5068 circuit breaker action filters low duty cycle over-load conditions to avoid declaring a fault during
short duration load transients. The timer charges capacitor CT with 240µA when the SENSE voltage is greater
than 50mV. When the SENSE pin voltage falls below 50mV, a 6µA current discharges the TIMER capacitor.
Repetitive over-current faults with duty cycle greater than 2.5% will eventually charge CT and trip the fault timer.
This feature protects the pass MOSFET which has a fast heating and slow cooling characteristic.
12
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Latch-Off and Auto-Retry
If the fault conditions persist long enough for TIMER to charge CT to 4V, the LM5068 latches off (LM5068-1, -3)
or switches off and initiates the re-try timer (LM5068-2, -4).
At the fault condition, after reaching the 4V, the TIMER pin will continue to ramp-up with 6µA current source until
it reaches the internal regulated voltage, which is equivalent to the saturation GATE drive voltage. The LM5068-1
and LM5068-3 remains off until the controller is reset by either temporarily pulling the UV pin low, pulling the
TIMER pin below 1 volt, or decreasing the input voltage below the internal VDD under-voltage lockout (UVLO)
threshold.
The LM5068-2 and LM5068-4 respond to a fault condition by pulling the GATE and TIMER pins low and then
initiating a timer sequence for automatic re-try. The re-try timer sequence begins with CT capacitor being charged
slowly to 4V with a 6µA current source and then discharged quickly to 1V with a 30mA discharge current. After 8
charge/discharge cycles the GATE pin is released and charged with a 60µA current source. If the fault condition
persists, the LM5068 will again turn off the MOSFET and another 8-cycle fault timer sequence will begin.
Power Good Flag
The power good flag (PWRGD) is activated when the MOSFET GATE is fully enhanced (>8V) and the voltage
input UV and OV comparators are satisfied. The power good output is a 90V capable open drain N-Channel
MOSFET. The LM5068-1 and LM5068-2 provide an active HIGH power-good state, while the LM5068-3 and
LM5068–4 are configured for an active LOW power-good state. The UV comparator, OV comparator, VDD UVLO,
or a circuit breaker time-out will reset the power good flag.
Internal Soft-Start
An internal soft-start feature ramps the (positive) input of the analog current limit amplifier during initial start-up.
The ramp duration is approximately 200µs. This feature reduces the load current slew rate (di/dt) at start-up.
Design Information
The LM5068 contains an internal regulator enabling the VDD pin to be connected directly to the line voltage from
10 to 90V. A local RC filter (0.1µF ceramic capacitor and 499Ω resistor) connected between VDD and VEE is
recommended to filter supply transients that exceed the 100V Absolute Maximum Rating.
UV and OV Thresholds and Voltage Divider Selection for R1, R2, and R3
Two comparators detect under-voltage and over-voltage conditions at the UV and OV pins. The threshold
voltages (VUV , VOV) of the UV and OV comparators are nominally 2.5V. Hysteresis is accomplished by 20µA
current sources (IUVHCS), into the external resistor divider connected to the UV and OV pins as shown in
Figure 25
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Vsupply
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UV HYSTERESIS CS
RF
VDD
20PA
R1
CF
+
2.5V
+
UV
R2
OV
+
2.5V
R3
20PA
VEE
OV HYSTERESIS CS
LM5068
Figure 25. UV/OV Setting
Hysteresis is necessary to prevent a possible “chattering” condition when the controller enables or disables the
external MOSFET. The change in line current interacts with the line impedance. This interaction can cause
several rapid on/off cycles on the MOSFET. A hysteresis window larger than the line impedance voltage drop
prevents this condition.
The impedance seen looking into the resistor divider from the UV and OV pin determines the hysteresis level.
UV/OV ON and OFF thresholds are calculated as follow:
R1
UV turn-on =
UV turn-off =
VUV + VUV + IUVHCSR1
R 2 + R3
R 1 + R 2 + R3
R2 + R3
OV turn-off =
VUV
R1 + R2 + R 3
R3
VOV
OV turn-on =
R3
(1)
(2)
VOV
(3)
- IUVHCS (R1 + R2) + VOV
(4)
The independent UV and OV pins provide complete flexibility for the user to select the operational voltage range
of the system. However, due to the UV Abs Max rating, the UV and OV thresholds can't be simultaneously set to
extremes in one resistor string. For the wide ranges of input voltages (i.e. UV threshold to12V and OV threshold
to 90V) it is recommended to use two separate voltage dividers to set the UV and OV thresholds independently.
14
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The typical operating ranges of under-voltage and over-voltage thresholds are calculated from the above
equations with known resistors. For example, for resistor values: R1=130KΩ, R2=5.5KΩ, and R3=4.5KΩ, the
computed thresholds are:
• UV turn-on = 37.60V
• UV turn-off = 35.0V
• OV turn-off = 77.78V
• OV turn-on = 75.07V
To maintain the threshold's accuracy, a resistor tolerance of 1% or better is recommended.
Calculation of Normal, Circuit Breaker, and Retry Timing
The CT capacitor at the TIMER pin controls the timing functions of the LM5068. When the interlock conditions are
met the timer capacitor is charged to 4V in a slow initial delay time period tIDT calculated from:
tIDT =
4V x CT
6 PA
(5)
If the SENSE pin detects more than 50mV across RS, the TIMER pin charges CT with 240µA. The Circuit
Breaker timeout period tCBT is calculated from:
tCBT =
4V x CT
240PA
(6)
When the LM5068-2 or LM5068-4 is latched, it pulls down the GATE pin and initiates eight, 6µA charging cycles
between 1V and 4V on CT. The total re-try time period tRT is given by:
tRT =
8 x 3V x CT
6PA
(7)
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Sense Resistor (Rs), Timer Capacitor (CT) and N-Channel Mosfet (Q1) Selection
To select the proper MOSFET, the following safe operating area (SOA) parameters are needed: maximum input
voltage, maximum current and the maximum current conduction time.
First, RS is calculated for the maximum operating load current (IL(MAX)) and the minimum circuit breaker trip point
(VCB(MIN)):
VCB(MIN)
RS =
IL(MAX)
40mV
=
IL(MAX)
(8)
During the initial charging process, the LM5068 may operate the MOSFET in current limit, forcing VAC(MIN) (80mV)
to VAC(MAX) (120mV) across RS.
The minimum in-rush current and maximum short-circuit limit are calculated from:
IINRUSH(MIN) =
80mV
RS
ISHORT-CIRCUIT(MAX) =
(9)
120mV
RS
(10)
The value of TIMER capacitor (CT) is calculated in order to prevent CT from timing out before the load capacitor
is fully charged using the slowest expected charging rate of the load capacitor. Assuming there is no initial
resistive loading, the time necessary to charge the load capacitor CL is calculated from:
CL x VIN(MAX)
tCL CHARGE =
IINRUSH(MIN)
(11)
Applying Equation 9 and Equation 11 to Equation 6 gives the TIMER capacitor value of:
CL x VIN(MAX) x RS x 240PA
CT =
4V x 80mV
(12)
Finally, the SOA curves of a prospective MOSFET are checked using VIN
from equation Equation 10 and time of the current flow from Equation 6.
(MAX),
and ISHORT-CIRCUIT
(MAX)
calculated
Example: For: IL=1A, VDD = 48V, VDD (MAX) = 100V and CL=100µF,
40mV
RS =
CT =
1A
= 40m:
(13)
100PF x 100V x 40m: x 240PA
= 300nF
4V x 80mV
(14)
To account for tolerances of RS, CL, TIMER current and TIMER threshold voltage, the computed CT value should
be increased, for this example 50% was selected, therefore:
CT = 300nF • 1.5 = 450nF
The maximum active current limiting value and duration are:
ISHORT-CIRCUIT(MAX) =
tCBT =
16
4V x CT
240PA
120mV
= 3A
40m:
(15)
4V x 450nF
= 7.5ms
=
240PA
(16)
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The N-channel MOSFET selection for use with the LM5068 controller in this example must be capable of
sustaining VDD=100V and I(MAX)=3A for 7.5ms in the worst case fault condition. A device that meets the
established criteria is the Vishay - 5UB85N10-10.
External Sense Resistor
Precise current measurement depends on the accuracy of the sense resistor (RS). For the optimal results, Kelvin
connection and close location of RS to the LM5068 should be considered. Figure 26 demonstrates PCB layout for
the Kelvin sensing.
The RS power rating should be greater than I2L*R, where IL is the normal maximum operating load.
GATE PIN
UV PIN
LM5068
VEE PIN
SENSE PIN
TO NEGATIVE
TERMINAL
OF
POWER
SOURCE
SENSE
RESISTOR
TO SOURCE
OF MOSFET
HIGH CURRENT PATH
Figure 26. Sense Resistor Connections
Timing Diagrams
Current Limit
Initial Timing
12 3
4
56
Normal Mode
7
VTHVT
6PA
6PA
TIMER
VTLVT
60PA
GATE
DRAIN
VAC
VCB
SENSE
PWRGD
Gate Ramp-up
Figure 27. System Power-Up Timing Behavior
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Assuming all of the initial conditions are met, the power-up sequence starts with Timer capacitor (CT) getting
charged. CT is charged with 6µA current source up to VTHVT (4V) then quickly discharge to VTLVT (1V). At time
point (2) the 60µA GATE current source is enabled. The GATE voltage increases until the MOSFET starts
conducting causing the SENSE voltage to increase until Active Current Limiting is activated (3). During the
current limiting period (3-4), CT is charged again, but there is not enough time to reach the 4V threshold before
the load capacitor is fully charged and the SENSE voltage falls below VCB. The GATE continues to fully enhance
the MOSFET and activating the PWRGD when the GATE voltage exceeds 8V (see Figure 27).
UV DROPS BELOW UV HIGH, GATE
AND TIMER ARE PULLED DOWN
UV CLEARS UV LOW, TIMER RAMPS
UP PROVIDED ALL INTERLOCK
CONDITIONS ARE MET
1 2
TIMER CLEARS VTLVT. GATE
VOLTAGE RAMPS UP
4
3
5 6
7
8 9 10 11
UV HIGH
UV
UV LOW
VTHVT
6 PA
240 PA
6 PA
VTLVT
TIMER
60 PA
GATE
60 PA
VAC
VCB
SENSE
PWRGD
DRAIN
INITIAL TIMING
GATE
RAMP-UP
Figure 28. Under-Voltage Timing Behavior
UV drops below UV HIGH (time point 1) puts the controller into a disabled mode. Later, UV increases over the
UV LOW threshold (time point 3), which initiates a system power-up sequence.
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OV PIN OVERSHOOTS OV HIGH, GATE IS
PULLED DOWN. PGOOD IS PULLED
LOW AND TIMER IS UNAFFECTED
1 2
OV DROPS BELOW OV LOW, GATE STARTS
RAMPING UP AND PGOOD BECOMES HIGH
WHEN GATE VOLTAGE REACHES VG
3 4 5
6 7
OV LOW
OV HIGH
OV
VTHVT
230 PA
6 PA
TIMER
GATE
60 PA
VG
60 PA
VAC
VCB
SENSE
PWRGD
Figure 29. Over-Voltage Timing Behavior
During normal operation, if the OV pin exceeds OV HIGH, as shown at time point 1 in the above diagram, the
TIMER status is unaffected. The GATE and PWRGD ( for LM5068-1 & -2) pins are pulled low and the load is
disconnected. At time point 2, OV recovers and drops below the OV LOW threshold, the GATE start-up cycle
begins. If the load capacitor is completely depleted during OV conditions, a full start-up cycle is initiated.
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Normal Mode
1
2
VTHVT
240PA
TIMER
VTLVT
GATE
DRAIN
VAC
VCB
SENSE
PGOOD
Circuit Breaker
Limit
Figure 30. Circuit Breaker Current Limit Fault
The above timing waveform shows the circuit breaker current limit fault behavior. The timer capacitor is charged
with 240µA when the SENSE pin exceeds VCB. If the SENSE pin drops below VCB before the TIMER reaches
VTHVT, the timer capacitor will be discharged with 6µA. In the above figure when TIMER exceeds VTHVT, GATE is
pulled low immediately to disconnect power to the load.
Normal Mode
1 2
345
6
Normal Mode
VTHVT
240PA
6PA
TIMER
VTLVT
60PA
GATE
DRAIN
VAC
VCB
SENSE
PWRGD
HIGH
Analog
Circuit
Limit
Gate
Ramp-up
Figure 31. Analog Current Limit Fault
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Figure 31 shows analog current limit behavior when the SENSE pin voltage exceeds VAC for a period of time,
which activates the Analog Current Limit but never reaches the fault timer threshold. At that time the GATE is
regulated by the analog current limit amplifier loop. When the SENSE voltage falls below VAC, GATE is allowed
to charge with a 60µA current source. A compensation circuit consisting of a resistor and a capacitor in series,
connected between GATE and VEE stabilizes the current limit loop.
Normal Mode 1
2
VTHVT
VTLVT
TIMER
GATE
DRAIN
VFDC
SENSE
VAC
VCB
PWRGD
Fast Gate
Pull Down
Figure 32. Fast Current Limit Fault
In case of a severe fault (for example sudden short-circuit of the output load) the SENSE pin exceeds the VFDC
threshold and GATE immediately pulls down until the Active Current Limit loop establishes control of the current
in the MOSFET. Careful selection of TIMER capacitor and MOSFET with adequate current and voltage ratings
will prevent damage to MOSFET low impedance faults.
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Normal Mode
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1
2
Circuit Breaker
Timeout Mode
3 4
5 6 7 Normal Mode
VTHVT
240PA
6PA
TIMER
6PA
VTLVT
30mA
60PA
GATE
DRAIN
VAC
VCB
SENSE
PWRGD
Circuit
Breaker
Limit
Gate Ramp-up
Figure 33. Shutdown Cooling Timing Behavior
Figure 33 shows the timer behavior for LM5068-2, -4 during fault re-try time. During normal operation, whenever
the SENSE pin exceeds the 50mV, circuit breaker fault limit, the timer capacitor begins to charge. If the TIMER
pin voltage exceeds 4V, the GATE is pulled down immediately, and LM5068-2, -4 disconnects power to the load.
The TIMER starts the fault re-try cycle by discharging CT with 30mA to the VTLVT threshold. The TIMER then
charges CT with 6µA to the VTHVT threshold. After eight charging phases and nine discharging phases, LM50682, -4 initiates an automatic retry start-up cycle.
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Evaluation Board Schematic
GND
GND
J1
J2
-48V
TP8
UV/OV
TP1
VDD
R10
499:
R1
0:
R5
100k:
+
C5
100PF
+
-48V
C6
0.1PF
TP4
UV
R2
100k:
VEE
U1
TP5
OV
R3
4.02k:
VDD
8
OV
TIMER
7
3
UV
GATE
6
4
VEE
SENSE
5
1
PWRGD
2
TP6
TIMER
+
R4
3.40k:
C2
NOT USED
+
R9
0:
+
TP7
GATE
LM5068
C1
NOT USED
C4
0.33PF
VEE
+
R6
0:
C3
22nF
Q1
SUB85N10-10
R7
50m: :
F1
10A
TP2
VEE
R8
0:
TP3
SENSE
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LM5068
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PART
VALUE
C1
NOT USED
24
www.ti.com
PACKAGE
DESCRIPTION
PART NUMBER
C2
NOT USED
C3
0.022uF/ 50V
C0805
CAPACITOR, CERAMIC,KEMET
C0805C223K5RAC
C4
0.33uF / 50V
C0805
CAPACITOR,CERAMIC,KEMET
C0805C334K5RAC
C5
100uF / 100V
CAPACITOR, ALUMINIUM
ELECTROLYTIC, SURFACE
MOUNT,PANASONIC
EEV-FK2A101M
C6
0.1uF / 100V
C1206
CAPACITOR, CERAMIC, TDK
C3216X7R2A104KT
F1
10A FUSE
SMD_FUSE
J1
PCB terminal Blocks/ 10A
MOUSER TERMINAL BLOCKS
651-1727010
J2
PCB terminal Blocks/ 10A
MOUSER TERMINAL BLOCKS
651-1727010
Q1
100V / 60A
N-Channel Power
MOSFET,TO263
VISHAY
SUB85N10-10
R1
0
R1206
SMD RESISTOR, 1% TOL
CRCW12060000F
R2
100K
R1206
SMD RESISTOR, 1% TOL
CRCW12061003F
R3
4.02K
R0805
SMD RESISTOR, 1% TOL
CRCW08053401F
R4
3.04K
R0805
SMD RESISTOR, 1% TOL
CRCW08053040F
R5
100K
R0805
SMD RESISTOR, 1% TOL
CRCW08051003F
R6
0
R0805
SMD RESISTOR, 1% TOL
CRCW08050000F
R7
50m
R2512
SMD RESISTOR, 1% TOL
WSL-2512 .050F
R8
0
R1206
SMD RESISTOR, 1% TOL
CRCW12060000F
R9
0
R1206
SMD RESISTOR, 1% TOL
CRCW12060000F
SMD RESISTOR, 1% TOL
CRCW1206499RF
Texas Instruments
LM5068
R10
499
R1206
U1
LM5068
VSSOP-8
COOPER BUSSMAN FAST ACTING TR/SFT-10
FUSE TRON
(Digikey # 283-2439-2-ND)
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26
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SNVS254C – JANUARY 2004 – REVISED MARCH 2013
REVISION HISTORY
Changes from Revision B (March 2013) to Revision C
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 26
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM5068MM-2/NOPB
ACTIVE
VSSOP
DGK
8
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 105
S67B
LM5068MM-4/NOPB
ACTIVE
VSSOP
DGK
8
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 105
S69B
LM5068MMX-2/NOPB
ACTIVE
VSSOP
DGK
8
3500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 105
S67B
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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