Maxim MAX6495ATT/V+T 72v, overvoltage-protection switches/limiter controllers with an external mosfet Datasheet

19-3778; Rev 7; 8/09
KIT
ATION
EVALU
LE
B
A
IL
A
AV
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Features
The MAX6495–MAX6499 is a family of small, low-current, overvoltage-protection circuits for high-voltage
transient systems such as those found in automotive
and industrial applications. These devices monitor the
input voltage and control an external n-channel MOSFET
switch to isolate the load at the output during an input
overvoltage condition. The MAX6495–MAX6499 operate
over a wide supply voltage range from +5.5V to +72V.
The gate of the n-channel MOSFET is driven high while
the monitored input is below the user-adjustable overvoltage threshold. An integrated charge-pump circuit
provides a 10V gate-to-source voltage to fully enhance
the n-channel MOSFET. When the input voltage
exceeds the user-adjusted overvoltage threshold, the
gate of the MOSFET is quickly pulled low, disconnecting the load from the input. In some applications, disconnecting the output from the load is not desirable. In
these cases, the protection circuit can be configured to
act as a voltage limiter where the GATE output sawtooths to limit the voltage to the load (MAX6495/
MAX6496/MAX6499).
The MAX6496 supports lower input voltages and
reduces power loss by replacing the external reverse
battery diode with an external series p-channel MOSFET.
The MAX6496 generates the proper bias voltage to
ensure that the p-channel MOSFET is on during normal
operations. The gate-to-source voltage is clamped during load-dump conditions, and the p-channel MOSFET
is off during reverse-battery conditions.
o Wide Supply Voltage Range: +5.5V to +72V
o Overvoltage-Protection Switch Controller Allows
User to Size External n-Channel MOSFETs
o Fast Gate Shutoff During Overvoltage with 100mA
Sink Capability
o Internal Charge-Pump Circuit Ensures 10V
Gate-to-Source Enhancement for Low RDS(ON)
Performance
o n-Channel MOSFET Latches Off After an
Overvoltage Condition (MAX6497/MAX6499)
o Adjustable Overvoltage Threshold
o Thermal Shutdown Protection
o Supports Series p-Channel MOSFET for ReverseBattery Voltage Protection (MAX6496)
o POK Indicator (MAX6497/MAX6498)
o Adjustable Undervoltage Threshold (MAX6499)
o -40°C to +125°C Operating Temperature Range
o Small, 3mm x 3mm TDFN Package
The MAX6497/MAX6498 feature an open-drain, undedicated comparator that notifies the system if the output
falls below the programmed threshold. The MAX6497
keeps the MOSFET switch latched off until either the
input power or the SHDN pin is cycled. The MAX6498
will autoretry when VOVSET falls below 130mV.
These devices are available in small, thermally
enhanced, 6-pin and 8-pin TDFN packages and are
fully specified from -40°C to +125°C.
Ordering Information
PART
PIN-PACKAGE
TOP MARK
MAX6495ATT+T
6 TDFN-EP*
AJM
MAX6495ATT/V+T
6 TDFN-EP*
AUG
Ordering Information continued at end of data sheet.
Note: All devices are specified over the -40°C to +125°C operating
temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
*EP = Exposed pad.
/V denotes an automotive qualified part.
Selector Guide appears at end of data sheet.
Pin Configurations
TOP VIEW
OUTFB
GATE
GND
6
5
4
Applications
Automotive
Industrial
Telecom/Servers/Networking
MAX6495
FireWire®
Notebook Computers
1
2
3
IN
SHDN
OVSET
3mm x 3mm TDFN
FireWire is a registered trademark of Apple Computer, Inc.
Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1
MAX6495–MAX6499
General Description
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
ABSOLUTE MAXIMUM RATINGS
(All pins referenced to GND.)
IN, GATE, GATEP ...................................................-0.3V to +80V
SHDN, CLEAR .............................................-0.3V to (VIN + 0.3V)
POK, OUTFB ..........................................................-0.3V to +80V
GATE to OUTFB .....................................................-0.3V to +12V
GATEP to IN ...........................................................-12V to +0.3V
OVSET, UVSET, POKSET .......................................-0.3V to +12V
Current Sink/Source (All Pins).............................................50mA
All Other Pins to GND ..................................-0.3V to (VIN + 0.3V)
Continuous Power Dissipation (TA = +70°C)
6-Pin TDFN (derate 18.2mW/°C above +70°C) .........1455mW
8-Pin TDFN (derate 18.2mW/°C above +70°C) .........1455mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
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
(VIN = 14V, CGATE = 6nF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
Supply Voltage Range
Input Supply Current
SYMBOL
CONDITIONS
VIN
IIN
MIN
TYP
5.5
No load
150
15
24
SHDN = low (MAX6495/MAX6496)
24
32
5
5.25
VIN rising, enables GATE
VIN falling, disables GATE
4.75
155
VTH+
OVSET rising
VTH-
OVSET falling
1.18
VHYST
OVSET falling
5
OVSET Threshold Voltage
(MAX6497/MAX6498)
VTH+
OVSET rising
VTH-
OVSET falling
OVSET Threshold Voltage
(MAX6499)
VTH+
OVSET rising
VTH-
OVSET falling
UVSET Threshold Voltage
(MAX6499)
VTH+
UVSET rising
VTH-
UVSET falling
1.18
VHYST
OVSET falling
5
OVSET/UVSET Threshold
Hysteresis (MAX6499)
POKSET Threshold Voltage
(MAX6497/MAX6498)
POKSET Threshold
Hysteresis (MAX6497/
MAX6498)
OVSET, UVSET, POKSET
Input Current
Startup Response Time
GATE Rise Time
2
VPOKSET+ POKSET rising
1.22
0.494
1.22
0.505
1.24
1.22
1.22
1.24
1.24
GATE rising from GND to VOUTFB + 8V,
OUTFB = GND
V
V
%
0.518
1.26
1.26
V
V
V
%
1.26
1.18
5
-50
SHDN rising (Note 2)
1.26
1.18
POKSET falling
ISET
tSTART
1.24
µA
mV
0.13
VPOKSET- POKSET falling
VHYST
V
100
IN Undervoltage Lockout
Hysteresis
OVSET Threshold Hysteresis
(MAX6495/MAX6496)
UNITS
72.0
SHDN = high
SHDN = low (MAX6497/MAX6498/
MAX6499)
IN Undervoltage Lockout
OVSET Threshold Voltage
(MAX6495/MAX6496)
MAX
V
%
+50
nA
100
µs
1
ms
_______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
(VIN = 14V, CGATE = 6nF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
OVSET to GATE Propagation
Delay
tOV
UVSET to GATE, POKSET to
POK Propagation Delay
CONDITIONS
MIN
SET rising from VTH - 100mV to VTH + 100mV
POKSET, UVSET falling from VTH + 100mV to
VTH - 100mV
GATE Output High Voltage
VOH
GATE Output Low Voltage
VOL
GATE Charge-Pump Current
IGATE
GATE to OUTFB Clamp
Voltage
VCLMP
TYP
VOUTFB = VIN = 5.5V, RGATE to IN = 1MΩ
VOUTFB = VIN, VIN ≥ 14V, RGATE to IN = 1MΩ
MAX
UNITS
0.6
µs
20
µs
VIN + 3.4 VIN + 3.8 VIN + 4.2
VIN + 8
VIN + 10
GATE sinking 15mA, OUTFB = GND
VIN + 11
1
VIN = 5.5V, GATE sinking 1mA, OUTFB = GND
0.9
GATE = GND
100
V
V
µA
12
18
V
IN to GATEP Output Low
Voltage
IGATEP_SINK = 75µA, IGATEP_SOURCE = 1µA
7.5
11.7
V
IN to GATEP Clamp Voltage
VIN = 24V, IGATEP_SOURCE = 10µA
12
18
V
SHDN, CLEAR Logic-High
Input Voltage
VIH
SHDN, CLEAR Logic-Low
Input Voltage
VIL
1.4
V
0.4
SHDN Input Pulse Width
7
CLEAR Input Pulse Width
µs
0.5
SHDN, CLEAR Input
Pulldown Current
SHDN is Internally pulled down to GND
Thermal Shutdown
(Note 3)
0.6
1.0
µs
1.4
µA
+160
°C
Thermal-Shutdown
Hysteresis
20
°C
POKSET to POK Delay
(MAX6497/MAX6498)
35
µs
POK Output Low Voltage
(MAX6497/MAX6498)
POK Leakage Current
(MAX6497/MAX6498)
VOL
VIN ≥ 14V, POKSET = GND, ISINK = 3.2mA
0.4
VIN ≥ 2.8V, POKSET = GND, ISINK = 100µA
0.4
VPOKSET = 14V
100
V
nA
Note 1: Specifications to TA = -40°C are guaranteed by design and not production tested.
Note 2: The MAX6495–MAX6499 power up with the external MOSFET in off mode (VGATE = GND). The external MOSFET turns on
tSTART after all input conditions are valid.
Note 3: For accurate overtemperature-shutdown performance, place the device in close thermal contact with the external MOSFET.
_______________________________________________________________________________________
3
MAX6495–MAX6499
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VIN = +12V, TA = +25°C, unless otherwise noted.)
85
60
115.0
112.5
110.0
107.5
105.0
35
102.5
100.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
10
15
25
35
45
55
65
75
30
20
5
15
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
GATE VOLTAGE vs. SUPPLY VOLTAGE
SET = GND, IN = OUTFB = SHDN
SET = GND, IN = OUTFB = SHDN
6
3
3
0
0
5.4
15
25
35
45
55
65
75
5.3
RISING
5.1
5.0
4.9
4.8
FALLING
4.5
5
15
25
35
45
55
65
16.5
MAX6495 toc07
RISING
1.25
1.20
16.4
SET = OUTFB = GND
IN = SHDN
16.3
16.2
16.1
16.0
15.9
15.8
15.7
1.15
FALLING
1.10
4
-40 -25 -10 5 20 35 50 65 80 95 110 125
GATE TO OUTFB CLAMP VOLTAGE
vs. TEMPERATURE
VGATE - VOUTFB (V)
SET THRESHOLD (V)
1.30
75
TEMPERATURE (°C)
SET THRESHOLD vs. TEMPERATURE
1.35
75
5.2
SUPPLY VOLTAGE (V)
IN = SHDN
65
4.7
SUPPLY VOLTAGE (V)
1.40
55
SET = GND, IN = OUTFB = SHDN
4.6
5
45
5.5
UVLO THRESHOLD (V)
VIN - VGATEP (V)
9
6
35
UVLO THRESHOLD vs. TEMPERATURE
GATEP VOLTAGE vs. SUPPLY VOLTAGE
9
25
SUPPLY VOLTAGE (V)
12
MAX6495 toc04
12
MAX6495 toc03
40
10
MAX6495 toc05
5
SET = GND, SHDN = GND
MAX6496
MAX6495 toc08
110
50
SHUTDOWN SUPPLY CURRENT (µA)
117.5
MAX6495 toc02
SET = GND, GATE ENHANCED
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
120.0
MAX6495 toc01
SET = GND, GATE ENHANCED
135
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT vs. TEMPERATURE
MAX6495 toc06
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
VGATE - VIN (V)
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
15.6
15.5
-40 -25 -10 5 20 35 50 65 80 95 110 125
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
TEMPERATURE (°C)
_______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
STARTUP WAVEFORM
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
STARTUP FROM SHUTDOWN
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
MAX6495 toc10
MAX6495 toc09
VIN
10V/div
VSHDN
1V/div
VGATE
10V/div
VGATE
10V/div
VOUT
10V/div
VOUT
10V/div
400µs/div
400µs/div
OVERVOLTAGE SWITCH FAULT
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
OVERVOLTAGE LIMITER
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
MAX6495 toc12
MAX6495 toc11
VIN
20V/div
VIN
20V/div
VGATE
20V/div
VGATE
20V/div
VOUT
20V/div
200µs/div
VOUT
20V/div
TRIP THRESHOLD = 28V
400µs/div
_______________________________________________________________________________________
5
MAX6495–MAX6499
Typical Operating Characteristics (continued)
(VIN = +12V, TA = +25°C, unless otherwise noted.)
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
MAX6495–MAX6499
Pin Description
6
MAX6495
MAX6496
MAX6497/MAX6498
MAX6499
PIN
1
1
1
1
IN
2
2
2
2
SHDN
NAME
3
3
3
3
OVSET
4
5
5
5
GND
5
6
6
6
GATE
6
7
7
7
OUTFB
FUNCTION
Positive Supply Voltage. Connect IN to the positive side of the input voltage. Bypass IN
with a 10µF capacitor to GND.
Shutdown Input. Drive SHDN low to force GATE low and turn off the external n-channel
MOSFET. Drive SHDN low and then high to reset the overvoltage-condition latch. SHDN
is internally pulled to GND with 1µA of current. Connect SHDN to IN for normal operation.
Overvoltage-Threshold Adjustment Input. Connect OVSET to an external resistive
voltage-divider network to adjust the desired overvoltage-disable or overvoltage-limit
threshold. Connect the resistor network to the input side (drain) of the n-channel
MOSFET for overvoltage switch turn-off applications or to the output side (source) of the
n-channel MOSFET for overvoltage-limiting applications (MAX6495/MAX6496/MAX6499).
Ground
Gate-Driver Output. Connect GATE to the gate of the external n-channel MOSFET switch.
GATE is the output of a charge pump with a 100µA pullup current to 10V (typ) above IN
during normal operation. GATE is quickly clamped to OUTFB during an overvoltage
condition. GATE pulls low when SHDN is low.
Output-Voltage-Sense Input. Connect OUTFB to the source of the external n-channel
MOSFET switch.
p-Channel Gate-Driver Output. Connect GATEP to the gate of an external p-channel
MOSFET to provide low-drop reverse-voltage protection. GATEP is biased to ensure that
the p-channel MOSFET is on during normal operating modes, the gate-to-source is not
overstressed during load-dump/overvoltage conditions, and the p-channel MOSFET is
off during reverse-battery conditions.
No Connection. Not internally connected.
—
4
—
—
GATEP
—
8
—
—
N.C.
—
—
4
—
POK
Power-OK Output. POK is an open-drain output. POK remains low while POKSET is
below the internal POKSET threshold. POK goes high impedance when POKSET goes
above the internal POKSET threshold. Connect POK to an external pullup resistor.
Power-OK Threshold-Adjustment Input. POK remains low while POKSET is below the
internal POKSET threshold (1.18V). POK goes high impedance when POKSET goes
above the internal POKSET threshold (1.24V). Connect a resistive divider from OUTFB
to POKSET to adjust the desired undervoltage threshold.
—
—
8
—
POKSET
—
—
—
4
CLEAR
Latch Clear Input. Connect CLEAR to a logic-high to latch the device off after an
overvoltage condition. With OVSET below VTH, pulse CLEAR low (5µs typ)
to reset the output latch. Connect CLEAR to GND to make the latch transparent.
—
—
—
8
UVSET
Undervoltage-Threshold Adjustment Input. Connect UVSET to an external resistive
voltage-divider network to adjust the desired undervoltage threshold.
—
—
—
—
EP
Exposed Pad. EP is internally connected to GND. Connect EP to the ground plane to
provide a low thermal-resistance path from the IC junction to the PC board. Do not use
as the primary electrical connection to GND.
_______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Overvoltage Monitoring
VOUT
VIN
When operating in overvoltage mode, the MAX6495–
MAX6499 feedback path (Figure 1) consists of IN,
OVSET’s internal comparator, the internal gate charge
pump, and the external n-channel MOSFET, resulting in
a switch-on/off function. When the programmed overvoltage threshold is tripped, the internal fast comparator turns off the external MOSFET, clamping GATE to
OUTFB within 0.5µs and disconnecting the power
source from the load. When IN decreases below the
adjusted overvoltage threshold, the MAX6495–MAX6499
slowly enhance GATE above OUTFB, reconnecting the
load to the power source.
MAX6495–MAX6499
Detailed Description
GATE
IN
OUTFB
MAX6495–
MAX6499
R1
OVSET
R2
GND
Overvoltage Limiter
(MAX6495/MAX6496/MAX6499)
When operating in overvoltage-limiter mode, the
MAX6495/MAX6496/MAX6499 feedback path (Figure 2)
consists of OUTFB, OVSET’s internal comparator, the
internal gate charge pump, and the external n-channel
MOSFET, resulting in the external MOSFET operating
as a voltage regulator.
During normal operation, GATE is enhanced 10V above
OUTFB. The external MOSFET source voltage is monitored through a resistive divider between OUTFB and
OVSET. When OUTFB rises above the adjusted overvoltage threshold, an internal comparator sinks the
charge-pump current, discharging the external GATE,
regulating OUTFB at the OVSET overvoltage threshold.
OUTFB remains active during the overvoltage transients
and the MOSFET continues to conduct during the overvoltage event, operating in switched-linear mode.
As the transient begins decreasing, OUTFB fall time will
depend on the MOSFET’s GATE charge, the internal
charge-pump current, the output load, and the tank
capacitor at OUTFB.
For fast-rising transients and very large-sized MOSFETs,
add an additional bypass capacitor from GATE to GND to
reduce the effect of the fast-rising voltages at IN. The
external capacitor acts as a voltage-divider working
against the MOSFET’s drain-to-gate capacitance. For a
6000pF gate-to-source capacitance, a 0.1µF capacitor at
GATE will reduce the impact of the fast-rising VIN input.
Caution must be exercised when operating the
MAX6495/MAX6496/MAX6499 in voltage-limiting mode
for long durations. If the VIN is a DC voltage greater than
the MOSFET’s maximum gate voltage, the MOSFET dissipates power continuously. To prevent damage to the
external MOSFET, proper heatsinking should be implemented.
Figure 1. Overvoltage Threshold (MAX6495–MAX6499)
VOUT
VIN
COUT
GATE
IN
OUTFB
MAX6495
MAX6496
MAX6499
R1
OVSET
GND
R2
Figure 2. Overvoltage-Limiter Protection Switch Configuration
GATE Voltage
The MAX6495–MAX6499 use a high-efficiency charge
pump to generate the GATE voltage. Upon VIN exceeding the 5V (typ) UVLO threshold, GATE enhances 10V
above VIN (for VIN ≥ 14V) with a 100µA pullup current.
An overvoltage condition occurs when the voltage at
OVSET goes above its V TH+ threshold. When the
threshold is crossed, GATE falls to OUTFB within 0.5µs
with a 100mA pulldown current. The MAX6495–MAX6499
include an internal clamp to OUTFB that ensures GATE
is limited to 18V (max) above OUTFB to prevent gateto-source damage of the external MOSFET.
_______________________________________________________________________________________
7
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
The gate cycles during overvoltage-limit and overvoltage-switch modes are quite similar but have distinct
characteristics. In overvoltage-switch mode, GATE is
enhanced to (VIN + 10V) while the monitored VIN voltage remains below the overvoltage fault threshold
(OVSET < VTH+). When an overvoltage fault occurs
(OVSET ≥ VTH+), GATE is pulled one diode drop below
OUTFB, turning off the external MOSFET and disconnecting the load from the input. GATE remains low
(MOSFET off) as long as the VIN voltage is above the
overvoltage fault threshold. As VIN falls back below the
overvoltage fault threshold, GATE is again enhanced to
(VIN + 10V).
In overvoltage-limit mode, GATE is enhanced to (VIN
+10V) while the monitored OUTFB voltage remains
below the overvoltage fault threshold (OVSET < VTH+).
When an overvoltage fault occurs (OVSET ≥ V TH+),
GATE is pulled one diode drop below OUTFB until
OUTFB drops 5% below the overvoltage fault threshold
(MAX6495/MAX6496/MAX6499). GATE is then turned
back on until OUTFB reaches the overvoltage fault
threshold and GATE is again turned off. GATE cycles in
a sawtooth waveform until OUTFB remains below the
overvoltage fault threshold and GATE remains constantly on (VIN +10V). The overvoltage limiter’s sawtooth GATE output operates the MOSFET in a
switched-linear mode while the input voltage remains
above the overvoltage fault threshold. The sawtooth frequency depends on the load capacitance, load current,
and MOSFET turn-on time (GATE charge current and
GATE capacitance).
GATE goes high when the following startup conditions
are met: VIN is above the UVLO threshold, SHDN is
high, an overvoltage fault is not present, and the device
is not in thermal shutdown.
⎛ R
⎞
VTRIPLOW = (VTH− ) ⎜ TOTAL ⎟
⎝ R2 + R3 ⎠
⎛R
⎞
VTRIPHIGH = (VTH+ ) ⎜ TOTAL ⎟
⎝ R3 ⎠
where RTOTAL = R1 + R2 + R3.
Use the following steps to determine the values for R1,
R2, and R3:
1) Choose a value for RTOTAL, the sum of R1, R2, and
R3. Because the MAX6499 has very high input
impedance, RTOTAL can be up to 5MΩ.
2) Calculate R3 based on R TOTAL and the desired
upper trip point:
R3 =
VTH+ × R TOTAL
VTRIPHIGH
3) Calculate R2 based on RTOTAL, R3, and the desired
lower trip point:
⎡ (VTH− ) × RTOTAL ⎤
R2 = ⎢
⎥ − R3
VTRIPLOW
⎢⎣
⎥⎦
4) Calculate R1 based on RTOTAL, R2, and R3:
R1 = RTOTAL – R2 – R3
To improve ESD protection, keep R3 ≥ 1kΩ.
DC-DC
CONVERTER
IN
VIN
Undervoltage Monitoring (MAX6499)
The MAX6499 includes undervoltage and overvoltage
comparators for window detection (see Figures 3 and
12). GATE is enhanced and the n-channel MOSFET is
on when the monitored voltage is within the selected
“window.” When the monitored voltage falls below the
lower limit (V TRIPLOW ) or exceeds the upper limit
(VTRIPHIGH) of the window, GATE falls to OUTFB turning off the MOSFET. The application in Figure 3 shows
the MAX6499 enabling the DC-DC converter when the
monitored voltage is in the selected window.
The resistor values R1, R2, and R3 can be calculated
as follows:
IN
R1
GATE
OUTFB
SHDN
UVSET
MAX6499
R2
OVSET
R3
CLEAR
GND
Figure 3. MAX6499 Window-Detector Circuit
8
_______________________________________________________________________________________
OUT
GND
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Setting Overvoltage Thresholds
OVSET provides an accurate means to set the overvoltage level for the MAX6495–MAX6499. Use a resistive
divider to set the desired overvoltage condition (see
Figure 2). OVSET has a rising 1.24V threshold with a
5% falling hysteresis (MAX6495/MAX6496/MAX6499)
and a rising 0.505V threshold with a falling 0.15V
threshold (MAX6497/MAX6498).
Overvoltage Latch Function
The MAX6497/MAX6499 offers a latch function that prevents the external MOSFET from turning on until the
latch is cleared. For the MAX6497, the latch can be
cleared by cycling the power on the input IN to a voltage below the undervoltage lockout or by pulling the
shutdown input low and then back to a logic-high
state. The MAX6499 offers a CLEAR input that latches
the n-MOSFET off when CLEAR is high. The latch is
removed when the CLEAR input is plused low. Connect
CLEAR low to make the latch transparent.
Overvoltage Retry Function
The MAX6498 offers an automatic retry function that
tries to enhance the external n-channel MOSFET after
the overvoltage condition is removed. When the monitored
input voltage detects an overvoltage condition (VSET >
VTH+), the n-MOSFET is turned off. The MOSFET stays off
until the voltage at VSET falls below its VTH- (typically
0.13V), at which point the output tries to turn on again.
Applications Information
Load Dump
Most automotive applications run off a multicell “12V”
lead-acid battery with a nominal voltage that swings
between 9V and 16V (depending on load current,
charging status, temperature, battery age, etc.). The
battery voltage is distributed throughout the automobile
and is locally regulated down to voltages required by
the different system modules. Load dump occurs when
the alternator is charging the battery and the battery
becomes disconnected. The alternator voltage regulator is temporarily driven out of control. Power from the
alternator flows into the distributed power system and
elevates the voltage seen at each module. The voltage
spikes have rise times typically greater than 5ms and
decays within several hundred milliseconds but can
extend out to 1s or more depending on the characteristics of the charging system. These transients are capable of destroying sensitive electronic equipment on the
first “fault event.”
Begin by selecting the total end-to-end resistance, RTOTAL = R1 + R2. Choose RTOTAL to yield a total current
equivalent to a minimum 100 x ISET (OVSET’s input bias
current) at the desired overvoltage threshold.
For example:
With an overvoltage threshold (VOV) set to 20V for the
MAX6495/MAX6496/MAX6499, RTOTAL < 20V / (100 x
ISET), where ISET is OVSET’s 50nA (max) input bias current.
RTOTAL < 4MΩ
Use the following formula to calculate R2:
R2 = VTH+ ×
R TOTAL
VOV
where VTH+ is the 1.24V OVSET rising threshold and
VOV is the desired overvoltage threshold.
R2 = 248kΩ. Use a 249kΩ standard resistor.
R TOTAL = R2 + R1, where R1 = 3.751MΩ. Use a
3.74MΩ standard resistor.
A lower value for total resistance dissipates more power
but provides slightly better accuracy. To improve ESD
protection, keep R2 ≥ 1kΩ.
Reverse-Battery Protection
The MAX6496 is an overvoltage-protection circuit that is
capable of driving a p-channel MOSFET to prevent
reverse-battery conditions. This MOSFET eliminates the
need for external diodes, thus minimizing the input voltage drop (see Figure 8).
Inrush/Slew-Rate Control
Inrush current control can be implemented by placing a
capacitor from GATE to GND to slowly ramp up the
GATE, thus limiting the inrush current and controlling
GATE’s slew rate during initial turn-on. The inrush current can be approximated using the following equation:
IINRUSH =
COUT
× IGATE + ILOAD
CGATE
_______________________________________________________________________________________
9
MAX6495–MAX6499
Power-OK Output (MAX6497/MAX6498)
POK is an open-drain output that remains low when the
voltage at POKSET is below the internal POKSET
threshold (1.18V). POK goes high impedance when
POKSET goes above the internal POKSET threshold
(1.24V). Connect a resistive divider from OUTFB to
POKSET to adjust the desired undervoltage threshold.
Use a resistor in the 100kΩ range from POKSET to
GND to minimize current consumption.
where IGATE is GATE’s 100µA sourcing current, ILOAD
is the load current at startup, and COUT is the output
capacitor.
not exceed the absolute maximum junction-temperature
rating of TJ = +150°C.
MOSFET Selection
The MAX6495–MAX6499 activate an internal 100mA
pulldown on GATE when SHDN goes low, OVSET
exceeds its threshold or UVSET falls below its threshold.
Once the voltage on GATE falls below the OUTFB voltage, current begins to flow from OUTFB to the 100mA
pulldown through the internal clamp diode, discharging
the output capacitors.
Select external MOSFETs according to the application
current level. The MOSFET’s on-resistance (RDS(ON))
should be chosen low enough to have a minimum voltage drop at full load to limit the MOSFET power dissipation. Determine the device power rating to
accommodate an overvoltage fault when operating the
MAX6495/MAX6496/MAX6499 in overvoltage-limit mode.
During normal operation, the external MOSFET dissipates little power. The power dissipated in the MOSFET
during normal operation is:
P = ILOAD2 x RDS(ON)
where P is the power dissipated in the MOSFET, ILOAD
is the output load current, and RDS(ON) is the drain-tosource resistance of the MOSFET.
Most power dissipation in the MOSFET occurs during a
prolonged overvoltage event when operating the
MAX6495/MAX6496/MAX6499 in voltage-limiter mode.
The power dissipated across the MOSFET is as follows
(see the Thermal Shutdown in Overvoltage-Limiter
Mode section):
P = VDS x ILOAD
where VDS is the voltage across the MOSFET’s drain
and source.
Peak Power-Dissipation Limit
Depending on the output capacitance and the initial voltage, a significant amount of energy may be dissipated
by the internal 100mA pulldown. To prevent damage to
the device ensure that for a given overvoltage threshold,
the output capacitance does not exceed the limit provided in Figure 4. This output capacitance represents the
sum of all capacitors connected to OUTFB, including
reservoir capacitors and DC-DC input filter capacitors.
Thermal Shutdown in Overvoltage-Limiter Mode
When operating the MAX6495/MAX6496/MAX6499 in
overvoltage-limit mode for a prolonged period of time, a
thermal shutdown is possible. The thermal shutdown is
dependent on a number of different factors:
• The device’s ambient temperature
• The output capacitor (COUT)
• The output load current (IOUT)
• The overvoltage threshold limit (VOV)
Thermal Shutdown
When the junction temperature exceeds TJ = +160°C,
the thermal sensor signals the shutdown logic, turning
off the GATE output and allowing the device to cool.
The thermal sensor turns the GATE on again after the
IC’s junction temperature cools by 20°C. Thermal-overload protection is designed to protect the MAX6495–
MAX6499 and the external MOSFET in the event of current-limit fault conditions. For continuous operation, do
10
MAXIMUM OUTPUT CAPACITANCE
vs. OVERVOLTAGE THRESHOLD
100,000
MAX6495 fig04
The MAX6495–MAX6499 thermal-shutdown feature
turns off GATE if it exceeds the maximum allowable
thermal dissipation. Thermal shutdown also monitors
the PC board temperature of the external n-channel
MOSFET when the devices sit on the same thermal
island. Good thermal contact between the MAX6495–
MAX6499 and the external n-channel MOSFET is essential for the thermal-shutdown feature to operate effectively. Place the n-channel MOSFET as close to
possible to OUTFB.
MAXIMUM OUTPUT CAPACITANCE (µF)
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
10,000
1000
SAFE OPERATING AREA
100
10
0
10
20
30
40
50
60
OVERVOLTAGE THRESHOLD (V)
Figure 4. Safe Operating Area for 100mA Pulldown.
______________________________________________________________________________________
70
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
During an initial overvoltage occurrence, the discharge
time (∆t1) of COUT, caused by IOUT and IGATEPD. The
discharge time is approximately:
∆t1 = COUT
VOV × 0.95
(IOUT + IGATEPD )
where VOV is the overvoltage threshold, IOUT is the load
current, and IGATEPD is the GATE’s 100mA pulldown
current.
Upon OUT falling below the threshold point, the
MAX6495/MAX6496/MAX6499s’ charge-pump current
must recover and begins recharging the external GATE
voltage. The time needed to recharge GATE from -VD to
the MOSFET’s gate threshold voltage is:
∆t 2 = CISS
VGS(TH) + VD
IGATE
where C ISS is the MOSFET’s input capacitance,
VGS(TH) is the MOSFET’s gate threshold voltage, VD is
the internal clamp (from OUTFB to GATE) diode’s forward voltage (1.5V, typ) and IGATE is the charge-pump
current (100µA typ).
During ∆t2, COUT loses charge through the output load.
The voltage across C OUT (∆V 2) decreases until the
MOSFET reaches its V GS(TH) threshold and can be
approximated using the following formula:
GATE
OUTFB
∆t2
∆t1
∆t3
∆tOV
∆V2 = IOUT
∆t 2
COUT
Once the MOSFET VGS(TH) is obtained, the slope of the
output-voltage rise is determined by the MOSFET Qg
charge through the internal charge pump with respect
to the drain potential. The new rise time needed to
reach a new overvoltage event can be calculated using
the following formula:
∆t 3 ≅
QGD ∆VOUT
VGS IGATE
where QGD is the gate-to-drain charge.
The total period of the overvoltage waveform can be
summed up as follows:
∆tOV = ∆t1 + ∆t2 + ∆t3
The MAX6495/MAX6496/MAX6499 dissipate the most
power during an overvoltage event when IOUT = 0. The
maximum power dissipation can be approximated
using the following equation:
PDISS = VOV × 0.975 × IGATEPD ×
∆t1
∆t OV
The die-temperature increase is related to θJC (8.3°C/W
and 8.5°C/W for the MAX6495/MAX6496/MAX6499,
respectively) of the package when mounted correctly
with a strong thermal contact to the circuit board. The
MAX6495/MAX6496/MAX6499 thermal shutdown is
governed by the equation:
TJ = TA + PDISS (θJC +θCA) < +170°C
Based on these calculations, the parameters of the
MOSFET, the overvoltage threshold, the output load
current, and the output capacitors are external variables affecting the junction temperature. If these parameters are fixed, the junction temperature can also be
affected by increasing ∆t3, which is the time the switch
is on. By increasing the capacitance at the GATE pin,
∆t 3 increases as it increases the amount of time
required to charge up this additional capacitance
(75µA gate current). As a result, ∆tOV increases, there-
Figure 5. MAX6495/MAX6496/MAX6499 Timing
______________________________________________________________________________________
11
MAX6495–MAX6499
• The overvoltage waveform period (tOV)
• The power dissipated across the package (PDISS)
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
MAX6495–MAX6499
Typical Application Circuits
DC-DC
CONVERTER
DC-DC
CONVERTER
IN
IN
OUT
GND
GATE
12V IN
IN
GATE
12V
OUTFB
IN
OUTFB
MAX6496
MAX6495
SHDN
SHDN
OVSET
OVSET
GATEP
GND
GND
Figure 7. Overvoltage Limiter with Low-Voltage-Drop ReverseProtection Circuit (MAX6496)
Figure 6. Overvoltage Limiter (MAX6495)
DC-DC
CONVERTER
IN
OUT
EN GND
GATE
12V
DC-DC
CONVERTER
IN
12V
OUT
GND
OUTFB
IN
POKSET
IN
OUT
GND
R1
GATE
OUTFB
SHDN
SHDN
UVSET
MAX6497
MAX6498
OVSET
POK
OVSET
GND
R3
Figure 8. Overvoltage Protection to a DC-DC Converter
(MAX6497/MAX6498)
12
MAX6499
R2
CLEAR
GND
Figure 9. Overvoltage and Undervoltage Window Detector
(MAX6499)
______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
IN
IN
THERMAL
PROTECTION
THERMAL
PROTECTION
UVLO
UVLO
10V
CHARGE
PUMP
5V
10V
CHARGE
PUMP
5V
IGATEP_SOURCE
OVSET
GATE
OVSET
GATE
1.24V
OUTFB
GATEP
1.24V
10V
OUTFB
SHDN
SHDN
MAX6495
MAX6496
GND
GND
Figure 11. Functional Diagram (MAX6496)
Figure 10. Functional Diagram (MAX6495)
IN
IN
THERMAL
PROTECTION
THERMAL
PROTECTION
UVLO
UVLO
10V
CHARGE
PUMP
5V
10V
CHARGE
PUMP
5V
OVSET
OVSET
GATE
GATE
0.505V
1.24V
OUTFB
SHDN
POKSET
OUTFB
UVSET
SHDN
1.24V
POK
MAX6497
MAX6498
1.24V
GND
Figure 12. Functional Diagram (MAX6497/MAX6498)
MAX6499
CLEAR
GND
Figure 13. Functional Diagram (MAX6499)
______________________________________________________________________________________
13
MAX6495–MAX6499
Functional Diagrams
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Selector Guide
p-CHANNEL
DRIVER
POK
FUNCTION
UNDERVOLTAGE
LATCH/
AUTORETRY
PACKAGE CODE
OV Switch/Limiter
—
—
—
—
T633-2
OV Switch/Limiter
Yes
—
—
—
T833-2
MAX6497
OV Switch
—
Yes
—
Latch
T833-2
MAX6498
OV Switch
—
Yes
—
Autoretry
T833-2
MAX6499
OV/UV Switch/Limiter
—
—
Yes
Latch
T833-2
PART
FUNCTION
MAX6495
MAX6496
Pin Configurations (continued)
TOP VIEW
N.C. OUTFB GATE GND
8
7
6
POKSET OUTFB GATE GND
5
8
1
2
3
6
5
MAX6497
MAX6498
MAX6496
IN
7
4
1
SHDN OVSET GATEP
IN
3mm x 3mm TDFN
2
3
4
SHDN OVSET POK
3mm x 3mm TDFN
UVSET OUTFB GATE GND
8
7
6
5
MAX6499
1
IN
2
3
4
SHDN OVSET CLEAR
3mm x 3mm TDFN
14
______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
PART
PIN-PACKAGE
TOP MARK
Chip Information
PROCESS: BiCMOS
MAX6496ATA+T
8 TDFN-EP*
AOF
MAX6497ATA+T
8 TDFN-EP*
AOC
Package Information
MAX6498ATA+T
8 TDFN-EP*
AOD
MAX6499ATA+T
8 TDFN-EP*
AOE
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages.
Note: All devices are specified over the -40°C to +125°C operating
temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
*EP = Exposed pad.
/V denotes an automotive qualified part.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
6 TDFN
T633-2
21-0137
8 TDFN
T833-2
21-0137
______________________________________________________________________________________
15
MAX6495–MAX6499
Ordering Information (continued)
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Revision History
REVISION
NUMBER
REVISION
DATE
0
7/05
Initial release
1
12/05
Corrected text and formula in the Detailed Description.
2
1/07
Updated text in the Applications Information.
3
12/08
Updated package codes in the Selector Guide.
1, 13
4
1/09
Added automotive qualified part for MAX6495.
1, 14
5
3/09
Updated Electrical Characteristics, added Peak Power Dissipation Limit section
and new Figure 4. Renumbered subsequent figures throughout data sheet.
3, 9, 10–15
6
7/09
Corrected the MAX6495ATT/V+T top mark in the Ordering Information table from
AJM to AUG.
2
7
8/09
Updated Undervoltage Monitoring (MAX6499) and Setting Overvoltage
Thresholds sections.
DESCRIPTION
PAGES
CHANGED
—
10, 11
9
8, 9
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.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2009 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
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