MAX6495_12
更新时间：2024-09-18 12:49:59
品牌：MAXIM
描述：72V, Overvoltage-Protection Switches/ Limiter Controllers with an External MOSFET
概述
数据手册MAX6495_12 概述
72V, Overvoltage-Protection Switches/ Limiter Controllers with an External MOSFET 72V ，过压保护开关/限幅控制器，外置MOSFET
MAX6495_12 数据手册
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PDF下载19-3778; Rev 9; 2/12
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
5–MAX649
General Description
Features
o Wide Supply Voltage Range: +5.5V to +72V
The MAX6495–MAX6499 is a family of small, low-cur-
rent, 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.
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 R
Performance
DS(ON)
The gate of the n-channel MOSFET is driven high while
the monitored input is below the user-adjustable over-
voltage 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, disconnect-
ing the load from the input. In some applications, dis-
connecting 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 saw-
tooths to limit the voltage to the load (MAX6495/
MAX6496/MAX6499).
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 Reverse-
Battery 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
Ordering Information
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 dur-
ing load-dump conditions, and the p-channel MOSFET
is off during reverse-battery conditions.
PART
PIN-PACKAGE
6 TDFN-EP*
TOP MARK
AJM
MAX6495ATT+T
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.
The MAX6497/MAX6498 feature an open-drain, undedi-
cated 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
Selector Guide appears at end of data sheet.
will autoretry when V
falls below 130mV.
Pin Configurations
OVSET
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.
TOP VIEW
OUTFB GATE
GND
4
6
5
Applications
Automotive
Industrial
MAX6495
Telecom/Servers/Networking
®
FireWire
Notebook Computers
1
2
3
IN
SHDN OVSET
3mm x 3mm TDFN
Pin Configurations continued at end of data sheet.
FireWire is a registered trademark of Apple Computer, Inc.
________________________________________________________________ Maxim Integrated Products
1
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.
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
Continuous Power Dissipation (T = +70°C)
A
SHDN, CLEAR .............................................-0.3V to (V + 0.3V)
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
Soldering Temperature (reflow) .......................................+260°C
IN
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 (V + 0.3V)
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 = 14V, C
= 6nF, T = -40°C to +125°C, unless otherwise noted. Typical values are at T = +25°C.) (Note 1)
IN
GATE
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
5.5
TYP
MAX
72.0
150
UNITS
Supply Voltage Range
V
V
IN
SHDN = high
100
15
5–MAX649
SHDN = low (MAX6497/MAX6498/
MAX6499)
24
Input Supply Current
I
No load
µA
IN
SHDN = low (MAX6495/MAX6496)
24
5
32
IN Undervoltage Lockout
V
V
rising, enables GATE
4.75
1.22
5.25
V
IN
IN
IN Undervoltage Lockout
Hysteresis
falling, disables GATE
155
mV
V
OVSET rising
OVSET falling
1.24
1.18
1.26
TH+
OVSET Threshold Voltage
(MAX6495/MAX6496)
V
%
V
V
TH-
OVSET Threshold Hysteresis
(MAX6495/MAX6496)
V
OVSET falling
5
HYST
V
OVSET rising
OVSET falling
OVSET rising
OVSET falling
UVSET rising
UVSET falling
0.494
1.22
1.22
0.505
0.13
1.24
1.18
1.24
1.18
0.518
1.26
1.26
TH+
OVSET Threshold Voltage
(MAX6497/MAX6498)
V
TH-
V
TH+
OVSET Threshold Voltage
(MAX6499)
V
V
TH-
V
TH+
UVSET Threshold Voltage
(MAX6499)
V
V
TH-
OVSET/UVSET Threshold
Hysteresis (MAX6499)
V
OVSET falling
5
%
V
HYST
V
POKSET rising
POKSET falling
1.22
-50
1.24
1.18
1.26
+50
POKSET+
POKSET Threshold Voltage
(MAX6497/MAX6498)
V
POKSET-
POKSET Threshold
Hysteresis (MAX6497/
MAX6498)
V
POKSET falling
5
%
HYST
OVSET, UVSET, POKSET
Input Current
I
nA
µs
SET
Startup Response Time
t
SHDN rising (Note 2)
100
1
START
GATE rising from GND to V
OUTFB = GND
+ 8V,
OUTFB
GATE Rise Time
ms
2
_______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
5–MAX649
ELECTRICAL CHARACTERISTICS (continued)
(V = 14V, C
= 6nF, T = -40°C to +125°C, unless otherwise noted. Typical values are at T = +25°C.) (Note 1)
IN
GATE
A
A
PARAMETER
OVSET to GATE Propagation
Delay
SYMBOL
CONDITIONS
SET rising from V - 100mV to V + 100mV
MIN
TYP
MAX
UNITS
t
0.6
µs
OV
TH
TH
UVSET to GATE, POKSET to
POK Propagation Delay
POKSET, UVSET falling from V + 100mV to
TH
20
µs
V
V
V
V
- 100mV
TH
= V = 5.5V, R
to IN = 1MΩ
V
+ 3.4
V
+ 3.8
V
+ 4.2
IN
OUTFB
OUTFB
IN
GATE
IN
IN
GATE Output High Voltage
V
OH
= V
V
≥ 14V, R
to IN = 1MΩ
V
+ 8
V
+ 10
V
+ 11
IN
IN, IN
GATE
IN
IN
GATE sinking 15mA, OUTFB = GND
= 5.5V, GATE sinking 1mA, OUTFB = GND
1
GATE Output Low Voltage
GATE Charge-Pump Current
V
V
OL
V
0.9
IN
I
GATE = GND
100
µA
V
GATE
GATE to OUTFB Clamp
Voltage
V
12
18
CLMP
IN to GATEP Output Low
Voltage
I
_
= 75µA, I
_ = 1µA
7.5
12
11.7
18
V
V
GATEP SINK
GATEP SOURCE
IN to GATEP Clamp Voltage
V
= 24V, I
_
= 10µA
IN
GATEP SOURCE
SHDN, CLEAR Logic-High
Input Voltage
V
1.4
IH
V
SHDN, CLEAR Logic-Low
Input Voltage
V
0.4
1.4
IL
SHDN Input Pulse Width
CLEAR Input Pulse Width
7
µs
µs
0.5
1.0
SHDN, CLEAR Input
Pulldown Current
SHDN is Internally pulled down to GND
0.6
µA
°C
°C
Thermal Shutdown
(Note 3)
+160
20
Thermal-Shutdown
Hysteresis
POKSET to POK Delay
(MAX6497/MAX6498)
35
µs
V
V
V
≥ 14V, POKSET = GND, I
= 3.2mA
= 100µA
0.4
0.4
IN
IN
SINK
POK Output Low Voltage
(MAX6497/MAX6498)
V
OL
≥ 2.8V, POKSET = GND, I
SINK
POK Leakage Current
(MAX6497/MAX6498)
V
= 14V
100
nA
POKSET
Note 1: Specifications to T = -40°C are guaranteed by design and not production tested.
A
Note 2: The MAX6495–MAX6499 power up with the external MOSFET in off mode (V
= GND). The external MOSFET turns on
GATE
t
after all input conditions are valid.
START
Note 3: For accurate overtemperature-shutdown performance, place the device in close thermal contact with the external MOSFET.
_______________________________________________________________________________________
3
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Typical Operating Characteristics
(V = +12V, T = +25°C, unless otherwise noted.)
IN
A
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT vs. TEMPERATURE
120.0
117.5
115.0
112.5
110.0
107.5
105.0
102.5
100.0
50
40
30
20
10
SET = GND, GATE ENHANCED
SET = GND, SHDN = GND
MAX6496
SET = GND, GATE ENHANCED
135
110
85
60
35
10
-40 -25 -10
5
20 35 50 65 80 95 110 125
5
15
25
35
45
55
65
75
5
15
25
35
45
55
65
75
5–MAX649
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
UVLO THRESHOLD vs. TEMPERATURE
GATE VOLTAGE vs. SUPPLY VOLTAGE
GATEP VOLTAGE vs. SUPPLY VOLTAGE
5.5
5.4
5.3
5.2
5.1
5.0
4.9
4.8
4.7
4.6
4.5
12
9
12
9
SET = GND, IN = OUTFB = SHDN
SET = GND, IN = OUTFB = SHDN
SET = GND, IN = OUTFB = SHDN
RISING
6
6
3
3
FALLING
0
0
-40 -25 -10
5
20 35 50 65 80 95 110 125
5
15
25
35
45
55
65
75
5
15
25
35
45
55
65
75
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
GATE TO OUTFB CLAMP VOLTAGE
vs. TEMPERATURE
SET THRESHOLD vs. TEMPERATURE
1.40
1.35
1.30
1.25
1.20
1.15
1.10
16.5
16.4
16.3
16.2
16.1
16.0
15.9
15.8
15.7
15.6
15.5
IN = SHDN
SET = OUTFB = GND
IN = SHDN
RISING
FALLING
-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)
4
_______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
5–MAX649
Typical Operating Characteristics (continued)
(V = +12V, T = +25°C, unless otherwise noted.)
IN
A
STARTUP FROM SHUTDOWN
(C = 100µF, C = 10µF, R = 100Ω)
STARTUP WAVEFORM
(C = 100µF, C = 10µF, R = 100Ω)
OUT
MAX6495 toc09
IN
OUT
OUT
MAX6495 toc10
IN
OUT
V
IN
V
SHDN
10V/div
1V/div
V
GATE
V
GATE
10V/div
10V/div
V
OUT
V
OUT
10V/div
10V/div
400µs/div
400µs/div
OVERVOLTAGE LIMITER
(C = 100µF, C = 10µF, R = 100Ω)
OUT
MAX6495 toc12
OVERVOLTAGE SWITCH FAULT
(C = 100µF, C = 10µF, R = 100Ω)
IN
OUT
IN
OUT
OUT
MAX6495 toc11
V
IN
V
IN
20V/div
20V/div
V
GATE
20V/div
V
GATE
20V/div
V
OUT
20V/div
V
OUT
20V/div
TRIP THRESHOLD = 28V
400µs/div
200µs/div
_______________________________________________________________________________________
5
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Pin Description
PIN
NAME
FUNCTION
Positive Supply Voltage. Connect IN to the positive side of the input voltage. Bypass IN
with a 10µF capacitor to GND.
1
2
1
2
1
2
1
2
IN
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.
SHDN
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).
5–MAX649
3
3
3
3
OVSET
4
5
5
6
5
6
5
6
GND
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.
GATE
Output-Voltage-Sense Input. Connect OUTFB to the source of the external n-channel
MOSFET switch.
6
7
4
7
7
OUTFB
GATEP
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.
—
—
—
—
—
8
—
4
—
—
N.C.
POK
No Connection. Not internally connected.
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
Latch Clear Input. Connect CLEAR to a logic-high to latch the device off after an
—
—
—
—
—
—
—
—
—
4
8
CLEAR
UVSET
EP
overvoltage condition. With OVSET below V , pulse CLEAR low (5µs typ)
to reset the output latch. Connect CLEAR to GND to make the latch transparent.
TH
Undervoltage-Threshold Adjustment Input. Connect UVSET to an external resistive
voltage-divider network to adjust the desired undervoltage threshold.
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.
—
6
_______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
5–MAX649
Detailed Description
V
V
OUT
IN
Overvoltage Monitoring
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 over-
voltage threshold is tripped, the internal fast compara-
tor 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.
GATE
IN
OUTFB
MAX6495–
MAX6499
R1
R2
OVSET
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.
Figure 1. Overvoltage Threshold (MAX6495–MAX6499)
V
IN
V
OUT
C
OUT
During normal operation, GATE is enhanced 10V above
OUTFB. The external MOSFET source voltage is moni-
tored through a resistive divider between OUTFB and
OVSET. When OUTFB rises above the adjusted over-
voltage 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 over-
voltage event, operating in switched-linear mode.
GATE
IN
OUTFB
OVSET
MAX6495
MAX6496
MAX6499
R1
R2
GND
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.
Figure 2. Overvoltage-Limiter Protection Switch Configuration
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 Voltage
The MAX6495–MAX6499 use a high-efficiency charge
pump to generate the GATE voltage. Upon V exceed-
IN
ing the 5V (typ) UVLO threshold, GATE enhances 10V
GATE will reduce the impact of the fast-rising V input.
IN
above V (for V ≥ 14V) with a 100µA pullup current.
IN
IN
Caution must be exercised when operating the
MAX6495/MAX6496/MAX6499 in voltage-limiting mode
for long durations. If the V is a DC voltage greater than
IN
the MOSFET’s maximum gate voltage, the MOSFET dis-
sipates power continuously. To prevent damage to the
external MOSFET, proper heatsinking should be imple-
mented.
An overvoltage condition occurs when the voltage at
OVSET goes above its V threshold. When the
TH+
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 gate-
to-source damage of the external MOSFET.
_______________________________________________________________________________________
7
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
The gate cycles during overvoltage-limit and overvolt-
R
⎛
⎜
⎞
⎟
TOTAL
age-switch modes are quite similar but have distinct
characteristics. In overvoltage-switch mode, GATE is
V
= V
TH−
(
)
TRIPLOW
⎝ R2 + R3⎠
enhanced to (V + 10V) while the monitored V volt-
IN
IN
R
⎛
⎞
TOTAL
age remains below the overvoltage fault threshold
(OVSET < V ). When an overvoltage fault occurs
V
= V
TH+
(
)
⎜
⎝
⎟
⎠
TRIPHIGH
R
3
TH+
(OVSET ≥ V
), GATE is pulled one diode drop below
TH+
where R
= R1 + R2 + R3.
TOTAL
OUTFB, turning off the external MOSFET and discon-
necting the load from the input. GATE remains low
Use the following steps to determine the values for R1,
R2, and R3:
(MOSFET off) as long as the V voltage is above the
IN
overvoltage fault threshold. As V falls back below the
IN
1) Choose a value for R
, the sum of R1, R2, and
R3. Because the MAX6499 has very high input
impedance, R can be up to 5MΩ.
TOTAL
overvoltage fault threshold, GATE is again enhanced to
(V + 10V).
IN
TOTAL
In overvoltage-limit mode, GATE is enhanced to (V
IN
2) Calculate R3 based on R
upper trip point:
and the desired
TOTAL
+10V) while the monitored OUTFB voltage remains
below the overvoltage fault threshold (OVSET < V
).
),
TH+
When an overvoltage fault occurs (OVSET ≥ V
TH+
V
× R
TH+
TOTAL
R3 =
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 con-
V
TRIPHIGH
5–MAX649
3) Calculate R2 based on R
lower trip point:
, R3, and the desired
TOTAL
⎡
⎢
⎤
V
× R
TOTAL
(
)
TH−
V
R2 =
− R3
⎥
stantly on (V +10V). The overvoltage limiter’s saw-
IN
⎢
⎣
⎥
⎦
TRIPLOW
tooth GATE output operates the MOSFET in a
switched-linear mode while the input voltage remains
above the overvoltage fault threshold. The sawtooth fre-
quency depends on the load capacitance, load current,
and MOSFET turn-on time (GATE charge current and
GATE capacitance).
4) Calculate R1 based on R
, R2, and R3:
TOTAL
R1 = R
– R2 – R3
TOTAL
To improve ESD protection, keep R3 ≥ 1kΩ.
GATE goes high when the following startup conditions
DC-DC
CONVERTER
IN OUT
GND
are met: V is above the UVLO threshold, SHDN is
IN
high, an overvoltage fault is not present, and the device
is not in thermal shutdown.
V
IN
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
IN
GATE OUTFB
R1
SHDN
UVSET
OVSET
MAX6499
R2
R3
lower limit (V
) or exceeds the upper limit
TRIPLOW
(V
) of the window, GATE falls to OUTFB turn-
TRIPHIGH
ing 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.
CLEAR GND
The resistor values R1, R2, and R3 can be calculated
as follows:
Figure 3. MAX6499 Window-Detector Circuit
8
_______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
5–MAX649
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.
Setting Overvoltage Thresholds
OVSET provides an accurate means to set the overvolt-
age 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).
Begin by selecting the total end-to-end resistance, R
TO-
= R1 + R2. Choose R
to yield a total current
TAL
TOTAL
Overvoltage Latch Function
The MAX6497/MAX6499 offers a latch function that pre-
vents 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 volt-
age 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.
equivalent to a minimum 100 x I
(OVSET’s input bias
SET
current) at the desired overvoltage threshold.
For example:
With an overvoltage threshold (V ) set to 20V for the
OV
MAX6495/MAX6496/MAX6499, R
< 20V / (100 x
TOTAL
I
), where I
is OVSET’s 50nA (max) input bias current.
SET
SET
R
< 4MΩ
TOTAL
Use the following formula to calculate R2:
R
TOTAL
R2 = V
×
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
TH+
V
OV
where V
OV
is the 1.24V OVSET rising threshold and
TH+
V
is the desired overvoltage threshold.
input voltage detects an overvoltage condition (V
>
SET
R2 = 248kΩ. Use a 249kΩ standard resistor.
V
), the n-MOSFET is turned off. The MOSFET stays off
TH+
until the voltage at V
falls below its V
(typically
TH-
SET
R
= R2 + R1, where R1 = 3.751MΩ. Use a
TOTAL
3.74MΩ standard resistor.
0.13V), at which point the output tries to turn on again.
A lower value for total resistance dissipates more power
but provides slightly better accuracy. To improve ESD
protection, keep R2 ≥ 1kΩ.
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 regula-
tor 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 characteris-
tics of the charging system. These transients are capa-
ble of destroying sensitive electronic equipment on the
first “fault event.”
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 volt-
age 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 cur-
rent can be approximated using the following equation:
C
OUT
I
=
× I
+ I
INRUSH
GATE LOAD
C
GATE
_______________________________________________________________________________________
9
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
where I
is GATE’s 100µA sourcing current, I
not exceed the absolute maximum junction-temperature
rating of T = +150°C.
GATE
LOAD
is the output
is the load current at startup, and C
capacitor.
OUT
J
Peak Power-Dissipation Limit
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 volt-
age, 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 (R
should be chosen low enough to have a minimum volt-
age drop at full load to limit the MOSFET power dissipa-
tion. Determine the device power rating to
accommodate an overvoltage fault when operating the
MAX6495/MAX6496/MAX6499 in overvoltage-limit mode.
)
DS(ON)
Depending on the output capacitance and the initial volt-
age, 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 provid-
ed in Figure 4. This output capacitance represents the
sum of all capacitors connected to OUTFB, including
reservoir capacitors and DC-DC input filter capacitors.
During normal operation, the external MOSFET dissi-
pates little power. The power dissipated in the MOSFET
during normal operation is:
P = I
2 x R
LOAD
DS(ON)
where P is the power dissipated in the MOSFET, I
is the output load current, and R
source resistance of the MOSFET.
LOAD
is the drain-to-
DS(ON)
5–MAX649
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:
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):
• The device’s ambient temperature
P = V x I
• The output capacitor (C
)
DS
LOAD
OUT
where V
is the voltage across the MOSFET’s drain
• The output load current (I
)
DS
OUT
and source.
• The overvoltage threshold limit (V
)
OV
Thermal Shutdown
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 essen-
tial for the thermal-shutdown feature to operate effec-
tively. Place the n-channel MOSFET as close to
possible to OUTFB.
MAXIMUM OUTPUT CAPACITANCE
vs. OVERVOLTAGE THRESHOLD
100,000
10,000
1000
100
SAFE OPERATING AREA
When the junction temperature exceeds T = +160°C,
J
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-over-
load protection is designed to protect the MAX6495–
MAX6499 and the external MOSFET in the event of cur-
rent-limit fault conditions. For continuous operation, do
10
0
10
20
30
40
50
60
70
OVERVOLTAGE THRESHOLD (V)
Figure 4. Safe Operating Area for 100mA Pulldown.
10 ______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
5–MAX649
• The overvoltage waveform period (t
)
OV
∆t
2
∆V = I
• The power dissipated across the package (P
)
DISS
2
OUT
C
OUT
During an initial overvoltage occurrence, the discharge
time (∆t ) of C , caused by I and I . The
1
OUT
OUT
GATEPD
Once the MOSFET V
is obtained, the slope of the
output-voltage rise is determined by the MOSFET Q
GS(TH)
discharge time is approximately:
g
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:
V
× 0.05
OV
∆t = C
1
OUT
(I
+ I
)
OUT
GATEPD
where V is the overvoltage threshold, I
is the load
OV
OUT
current, and I
current.
is the GATE’s 100mA pulldown
GATEPD
Q
∆V
I
GATE
GD OUT
∆t
≅
3
V
GS
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 -V to
D
the MOSFET’s gate threshold voltage is:
where Q
is the gate-to-drain charge.
GD
The total period of the overvoltage waveform can be
summed up as follows:
∆t
OV =
∆t + ∆t + ∆t
1 2 3
V
+ V
D
GS(TH)
The MAX6495/MAX6496/MAX6499 dissipate the most
power during an overvoltage event when I = 0. The
∆t = C
2
ISS
OUT
I
GATE
maximum power dissipation can be approximated
using the following equation:
where C
GS(TH)
is the MOSFET’s input capacitance,
is the MOSFET’s gate threshold voltage, V is
the internal clamp (from OUTFB to GATE) diode’s for-
ward voltage (1.5V, typ) and I
current (100µA typ).
ISS
V
D
∆t
1
P
= V
× 0.975 × I
×
DISS
OV
GATEPD
∆t
is the charge-pump
GATE
OV
The die-temperature increase is related to θ (8.3°C/W
JC
During ∆t , C
loses charge through the output load.
2
OUT
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:
The voltage across C
(∆V ) decreases until the
2
OUT
MOSFET reaches its V
approximated using the following formula:
threshold and can be
GS(TH)
T = T + P
DISS
(θ +θ ) < +170°C
JC CA
J
A
Based on these calculations, the parameters of the
MOSFET, the overvoltage threshold, the output load
current, and the output capacitors are external vari-
ables affecting the junction temperature. If these para-
meters are fixed, the junction temperature can also be
GATE
∆t
2
affected by increasing ∆t , which is the time the switch
3
is on. By increasing the capacitance at the GATE pin,
∆t increases as it increases the amount of time
3
OUTFB
∆t
1
∆t
3
required to charge up this additional capacitance
∆t
OV
(75µA gate current). As a result, ∆t
increases, there-
DISS
OV
by reducing the power dissipated (P
).
Figure 5. MAX6495/MAX6496/MAX6499 Timing
______________________________________________________________________________________ 11
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Typical Application Circuits
DC-DC
DC-DC
CONVERTER
CONVERTER
IN
OUT
GND
IN
OUT
GND
GATE
GATE
12V
12V IN
IN
OUTFB
OVSET
IN
OUTFB
MAX6496
MAX6495
SHDN
SHDN
OVSET
GATEP
GND
GND
5–MAX649
Figure 6. Overvoltage Limiter (MAX6495)
Figure 7. Overvoltage Limiter with Low-Voltage-Drop Reverse-
Protection Circuit (MAX6496)
DC-DC
CONVERTER
DC-DC
CONVERTER
IN
OUT
IN
OUT
GND
12V
EN GND
GATE OUTFB
IN
GATE OUTFB
12V
IN
POKSET
R1
SHDN
SHDN
UVSET
OVSET
MAX6497
MAX6498
MAX6499
R2
R3
OVSET
POK
GND
CLEAR GND
Figure 8. Overvoltage Protection to a DC-DC Converter
(MAX6497/MAX6498)
Figure 9. Overvoltage and Undervoltage Window Detector
(MAX6499)
12 ______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
5–MAX649
Functional Diagrams
IN
IN
THERMAL
PROTECTION
THERMAL
PROTECTION
UVLO
UVLO
10V
CHARGE
PUMP
5V
10V
CHARGE
PUMP
I
GATEP_SOURCE
5V
OVSET
GATEP
GATE
OVSET
GATE
1.24V
OUTFB
SHDN
1.24V
10V
OUTFB
SHDN
MAX6495
MAX6496
GND
GND
Figure 10. Functional Diagram (MAX6495)
Figure 11. Functional Diagram (MAX6496)
IN
IN
THERMAL
PROTECTION
THERMAL
PROTECTION
UVLO
UVLO
10V
CHARGE
PUMP
10V
CHARGE
PUMP
5V
5V
OVSET
OVSET
GATE
GATE
0.505V
1.24V
OUTFB
OUTFB
SHDN
UVSET
SHDN
POKSET
1.24V
POK
1.24V
MAX6499
MAX6497
MAX6498
GND
CLEAR
GND
Figure 12. Functional Diagram (MAX6497/MAX6498)
Figure 13. Functional Diagram (MAX6499)
______________________________________________________________________________________ 13
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Selector Guide
p-CHANNEL
DRIVER
POK
LATCH/
PART
FUNCTION
UNDERVOLTAGE
PACKAGE CODE
FUNCTION
AUTORETRY
MAX6495
MAX6496
MAX6497
MAX6498
OV Switch/Limiter
OV Switch/Limiter
OV Switch
—
Yes
—
—
—
—
—
T633-2
T833-2
T833-2
T833-2
T833-2
—
—
Yes
Yes
—
—
Latch
Autoretry
Latch
OV Switch
—
—
MAX6499 OV/UV Switch/Limiter
—
Yes
Pin Configurations (continued)
TOP VIEW
N.C. OUTFB GATE GND
8 5
POKSET OUTFB GATE GND
5–MAX649
7
6
8
7
6
5
MAX6497
MAX6498
MAX6496
1
2
3
4
1
2
3
4
IN SHDN OVSET GATEP
IN SHDN OVSET POK
3mm x 3mm TDFN
3mm x 3mm TDFN
OUTFB GATE GND
UVSET
8
7
6
5
MAX6499
1
2
3
4
IN SHDN OVSET CLEAR
3mm x 3mm TDFN
14 ______________________________________________________________________________________
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
5–MAX649
Ordering Information (continued)
Chip Information
PROCESS: BiCMOS
PART
PIN-PACKAGE
8 TDFN-EP*
8 TDFN-EP*
8 TDFN-EP*
8 TDFN-EP*
8 TDFN-EP*
TOP MARK
AOF
MAX6496ATA+T
MAX6497ATA+T
MAX6498ATA+T
MAX6499ATA+T
MAX6499ATA/V+T
AOC
Package Information
AOD
For the latest package outline information and land patterns
(footprints), go to www.maxim-ic.com/packages. Note that a
"+", "#", or "-" in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
AOE
AOE
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
6 TDFN-EP
PACKAGE
CODE
T633+2
OUTLINE
NO.
21-0137
21-0137
LAND
PATTERN NO.
90-0058
90-0059
8 TDFN-EP
T833+2
______________________________________________________________________________________ 15
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
DESCRIPTION
CHANGED
0
1
2
3
4
7/05
12/05
1/07
Initial release.
—
10, 11
9
Corrected text and formula in the Detailed Description.
Updated text in the Applications Information.
Updated package codes in the Selector Guide.
Added automotive qualified part for MAX6495.
12/08
1/09
1, 13
1, 14
Updated Electrical Characteristics, added Peak Power Dissipation Limit section
and new Figure 4. Renumbered subsequent figures throughout data sheet.
5
6
7
3/09
7/09
8/09
3, 9, 10–15
Corrected the MAX6495ATT/V+T top mark in the Ordering Information table from
AJM to AUG.
2
Updated Undervoltage Monitoring (MAX6499) and Setting Overvoltage
Thresholds sections.
8, 9
5–MAX649
Added soldering temperature in the Absolute Maximum Ratings section and
corrected equation.
8
9
1/11
2/12
2, 11
15
Added automotive package for MAX6499.
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. The parametric values (min and max limits) shown in
the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2012 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX6495_12 相关器件
| 型号 | 制造商 | 描述 | 价格 | 文档 |
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|
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