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PDF MAX6495 Data sheet ( Hoja de datos )
| Número de pieza | MAX6495 | |
| Descripción | Overvoltage-Protection Switches/Limiter Controllers | |
| Fabricantes | Maxim Integrated Products | |
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19-3778; Rev 7; 8/09
EVAALVUAAILTAIOBNLEKIT
www.DataSheet4U.com
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
General Description
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.
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).
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.
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
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.
Applications
Automotive
Industrial
Telecom/Servers/Networking
FireWire®
Notebook Computers
FireWire is a registered trademark of Apple Computer, Inc.
Features
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 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
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
65
GND
4
MAX6495
12 3
IN SHDN OVSET
3mm x 3mm TDFN
Pin Configurations continued at end of data sheet.
________________________________________________________________ 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.
1 page  
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72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
Typical Operating Characteristics (continued)
(VIN = +12V, TA = +25°C, unless otherwise noted.)
STARTUP WAVEFORM
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
MAX6495 toc09
VIN
10V/div
VGATE
10V/div
STARTUP FROM SHUTDOWN
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
MAX6495 toc10
VSHDN
1V/div
VGATE
10V/div
VOUT
10V/div
VOUT
10V/div
400µs/div
400µs/div
OVERVOLTAGE SWITCH FAULT
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
MAX6495 toc11
VIN
20V/div
200µs/div
VGATE
20V/div
VOUT
20V/div
OVERVOLTAGE LIMITER
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
MAX6495 toc12
VIN
20V/div
TRIP THRESHOLD = 28V
400µs/div
VGATE
20V/div
VOUT
20V/div
_______________________________________________________________________________________ 5
5 Page 
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72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
• The overvoltage waveform period (tOV)
• The power dissipated across the package (PDISS)
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:
∆t2
=
CISS
VGS(TH) +
IGATE
VD
where CISS 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 for-
ward 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 COUT (∆V2) decreases until the
MOSFET reaches its VGS(TH) threshold and can be
approximated using the following formula:
GATE
∆t2
OUTFB
∆t1 ∆t3
∆tOV
Figure 5. MAX6495/MAX6496/MAX6499 Timing
∆V2
= IOUT
∆t2
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:
∆t3
≅
QGD
VGS
∆VOUT
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
∆tOV
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 vari-
ables affecting the junction temperature. If these para-
meters 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,
∆t3 increases as it increases the amount of time
required to charge up this additional capacitance
(75µA gate current). As a result, ∆tOV increases, there-
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet MAX6495.PDF ] | |
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