MAX6397TATA+ [MAXIM]
暂无描述;型号: | MAX6397TATA+ |
厂家: | MAXIM INTEGRATED PRODUCTS |
描述: | 暂无描述 开关 控制器 |
文件: | 总18页 (文件大小:300K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
19-3668; Rev 5; 1/09
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
7/MAX6398
General Description
Features
The MAX6397/MAX6398 are small, high-voltage overvolt-
age protection circuits. These devices disconnect the
output load or limit the output voltage during an input
overvoltage condition. These devices are ideal for appli-
cations that must survive high-voltage transients such as
those found in automotive and industrial applications.
o 5.5V to 72V Wide Supply Voltage Range
o Overvoltage Protection Controllers Allow User to
Size External n-Channel MOSFETs
o Internal Charge-Pump Circuit Ensures MOSFET
Gate-to-Source Enhancement for Low R
DS(ON)
The MAX6397/MAX6398 monitor the input or output
voltages and control an external n-channel MOSFET to
isolate or limit the load from overvoltage transient energy.
When the monitored input voltage is below the user-
adjustable overvoltage threshold, the external n-channel
MOSFET is turned on by the GATE output. In this mode,
the internal charge pump fully enhances the n-channel
MOSFET with a 10V gate-to-source voltage.
Performance
o Disconnect or Limit Output from Input During
Overvoltage Conditions
o Adjustable Overvoltage Threshold
o Thermal-Shutdown Protection
o Always-On, Low-Current (37µA) Linear Regulator
Sources Up to 100mA (MAX6397)
When the input voltage exceeds the overvoltage thresh-
old, the protection can disconnect the load from the
input by quickly forcing the GATE output low. 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.
o Fully Specified from -40°C to +125°C (T )
J
o Small, Thermally Enhanced 3mm x 3mm TDFN
Package
Ordering Information
The MAX6397 also offers an always-on linear regulator
that is capable of delivering up to 100mA of output
current. This high-voltage linear regulator consumes
only 37µA of quiescent current.
PART
TEMP RANGE
-40°C to +125°C
-40°C to +125°C
PIN-PACKAGE
8 TDFN-EP**
6 TDFN-EP**
MAX6397_ATA-T*
MAX6398ATT-T*
The regulator is offered with output options of 5V, 3.3V,
2.5V, or 1.8V. An open-drain, power-good output (POK)
asserts when the regulator output falls below 92.5% or
87.5% of its nominal voltage.
*Replace “-T” with “+T” for lead(Pb)-free/RoHS-compliant packages.
**EP = Exposed pad.
The MAX6397 linear regulator is offered in four output voltage
options and a choice of a 92.5% or 87.5% POK threshold
assertions. See the Selector Guide.
The MAX6397/MAX6398 include internal thermal-shut-
down protection, disabling the external MOSFET and
linear regulator if the chip reaches overtemperature
conditions. The devices operate over a wide 5.5V to
72V supply voltage range, are available in small TDFN
packages, and are fully specified from -40°C to
+125°C.
Selector Guide and Typical Operating Circuit appear at end
of data sheet.
Pin Configurations
TOP VIEW
REG OUT GATE GND
8
7
6
5
Applications
Automotive
Industrial
*EP
®
FireWire
MAX6397
Notebook Computers
Wall Cube Power Devices
1
2
3
4
IN SHDN SET POK
TDFN
FireWire is a registered trademark of Apple Computer, Inc.
*EXPOSED PAD. CONNECT TO GND.
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.
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
ABSOLUTE MAXIMUM RATINGS
(All pins referenced to GND, unless otherwise noted.)
IN, GATE, OUT ............................................................-0.3V to +80V
SHDN..................................................................-0.3V to (IN + 0.3V)
GATE to OUT .................................................................-0.3 to +20V
SET, REG, POK ...........................................................-0.3V to +12V
Maximum Current:
Continuous Power Dissipation (T = +70°C)
A
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 (T ) ......................-40°C to +125°C
A
Junction Temperature...........................................................+150°C
Storage Temperature Range .................................-65°C to +150°C
Lead Temperature ................................................................+300°C
IN, REG...............................................................................350mA
All Remaining Pins ...................................................................50mA
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional oper-
ation 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
= 6000pF, C
= 4.7µF, T = T = -40°C to +125°C, unless otherwise noted. Typical values are at T = T = +25°C.) (Note 1)
J
J
IN
GATE
REG
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
72
UNITS
Supply Voltage Range
V
5.5
V
IN
SHDN = high, no load (MAX6397)
SHDN = high, (MAX6398)
118
104
37
140
130
45
Input Supply Current
µA
SHDN = low, no load (MAX6397)
SHDN = low, (MAX6398)
7/MAX6398
11
20
IN Undervoltage Lockout
V
rising, enables GATE
4.66
5
5.50
V
IN
IN Undervoltage Lockout
Hysteresis
V
falling, disables GATE
175
mV
IN
SET Threshold Voltage
SET Threshold Hysteresis
SET Input Current
V
With respect to GND
1.181
-50
1.215
4
1.248
+50
V
TH
V
%
HYST
I
nA
µs
SET
Startup Response Time
t
SHDN rising (Note 2)
100
1
START
GATE rising from GND to V
+ 8V,
OUT
GATE Rise Time
ms
µs
C
= 6000pF, OUT = GND
GATE
SET rising from V - 100mV to V
TH
100mV
+
TH
SET to GATE Propagation Delay
GATE Output High Voltage
t
0.75
OV
V
+
V
+
V
+
IN
IN
IN
V
V
= V = 6V, R
to IN = 1MΩ
OUT
OUT
IN
GATE
3.8V
4.2V
4.6V
V
V
OH
V
+
V
+
V
+
IN
IN
IN
= V ; V ≥ 14V, R
to IN = 1MΩ
IN IN
GATE
8.5V
9.2V
11.5V
GATE Output Low Voltage
V
GATE sinking 20mA, V
GATE = GND
= GND
OUT
0.38
V
µA
V
OL
GATE Charge-Pump Current
GATE to OUT Clamp Voltage
SHDN Logic-High Input Voltage
SHDN Logic-Low Input Voltage
I
75
1
GATE
V
13
18
CLMP
V
1.4
IH
V
0.4
IL
V
= 2V, SHDN is internally pulled
SHDN
SHDN Input Pulldown Current
µA
down to GND
Thermal Shutdown
(Note 3)
+150
20
°C
°C
Thermal Shutdown Hysteresis
REGULATOR (MAX6397)
I
I
= 1mA
40
60
48
REG
Ground Current
I
SHDN = GND
µA
GND
= 100mA
REG
2
_______________________________________________________________________________________
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
7/MAX6398
ELECTRICAL CHARACTERISTICS (continued)
(V = 14V; C
= 6000pF, C
= 4.7µF, T = T = -40°C to +125°C, unless otherwise noted. Typical values are at T = T = +25°C.) (Note 1)
J
J
IN
GATE
REG
A
A
PARAMETER
SYMBOL
CONDITIONS
= 1mA
MIN
4.925
4.85
TYP
MAX
5.120
5.15
UNITS
I
5
REG
MAX6397L/M
MAX6397S/T
MAX6397Y/Z
MAX6397V/W
1mA < I
< 100mA
REG
I
= 1mA
3.243
3.201
2.456
2.41
3.3
2.5
1.8
3.360
REG
1mA < IREG < 100mA
I = 1mA
REG
V
3. 360
2.542
2.55
REG Output Voltage
(V ≥ V + 1.8V)
V
REG
IN
REG
1mA < I
< 100mA
REG
I
= 1mA
1.760
1.715
1.837
1.837
0.12
REG
1mA < I
< 100mA
REG
mV/V
5.5V ≤ VIN ≤ 72V, I
5.5V ≤ VIN ≤ 72V, I
VIN = 14V
= 1mA, V
= 5V
REG
REG
REG
Dropout Voltage (Note 4)
Current Limit
∆VDO
= 100mA, V
= 5V
1.2
REG
150
300
mA
% of
Overvoltage-Protection Threshold
Overvoltage-Protection Sink Current
V
105
15
OVP
V
REG
I
V
= 1.1 x V
(nominal)
REG
mA
OVP
REG
6.5V ≤ VIN ≤ 72V, I
5.5V ≤ VIN ≤ 72V, I
5.5V ≤ VIN ≤ 72V, I
= 10mA, V
= 5V
0.22
0.05
REG
REG
REG
REG
∆ V
∆V
/
REG
Line Regulation (Note 5)
= 1mA, V
= 5V
mV/V
REG
REG
= 100mA, V
= 5V
1.5
REG
∆VREG /
∆IREG
Load Regulation
1mA ≤ I
≤ 100mA, V
= 5V
REG
0.8
mV/mA
REG
Power-Supply Rejection Ratio
Startup Response Time
I
= 10mA, f = 100Hz, 0.5V
55
dB
µs
REG
P-P
t
R
L
= 500Ω, V
= 5V, C
= 4.7µF
180
START
REG
REG
REG
4.500
4.230
2.966
2.805
2.250
2.125
1.590
1.524
4.67
4.780
4.500
3.140
2.970
2.375
2.250
1.696
1.625
M
T
4.375
3.053
2.892
2.304
2.188
1.653
1.575
35
S
POK Assertion Threshold
(MAX6397 Only)
V
V
POK_TH
Z
Y
W
V
REG to POK Delay
V
V
V
rising or falling
= 5V
µs
nA
V
REG
POK
POK Leakage Current
POK Output Low Voltage
300
0.3
V
≥ 1.5V, I
= 1.6mA, POK asserted
OL
IN
SINK
Note 1: Specifications to T = -40°C are guaranteed by design and not production tested.
A
Note 2: The MAX6397/MAX6398 power up with the external FET in off mode (V
= GND). The external FET turns on t
after the
GATE
START
device is powered up and all input conditions are valid.
Note 3: For accurate overtemperature shutdown performance, place the device in close thermal contact with the external MOSFET.
Note 4: Dropout voltage is defined as V - V when V is 2% below the value of V for V = V (nominal) + 2V.
IN
REG
REG
REG
IN
REG
Note 5: Operations beyond the thermal dissipation limit may permanently damage the device.
_______________________________________________________________________________________
3
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
Typical Operating Characteristics
(V = 14V, C
IN
= 4.7µF, I
= 0, unless otherwise noted.)
REG
REG
SUPPLY CURRENT
vs. INPUT VOLTAGE
SUPPLY CURRENT
vs. INPUT VOLTAGE
SUPPLY CURRENT vs. TEMPERATURE
180
160
120
110
100
90
MAX6397
170
MAX6397
GATE ON
MAX6398
GATE ON
140
120
100
80
160
150
140
130
120
110
100
90
V
= 72V
IN
80
70
V
= 14V
IN
60
60
50
80
40
40
3
-50 -25
0
25
50
75 100 125
0
10 20 30 40 50 60 70 80
INPUT VOLTAGE (V)
0
20
40
60
80
TEMPERATURE (°C)
INPUT VOLTAGE (V)
SUPPLY CURRENT
vs. TEMPERATURE
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE (MAX6397)
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
20
18
16
14
12
10
8
140
130
120
110
100
90
50
45
40
35
30
25
20
MAX6398
GATE OFF
MAX6398
GATE ON
REGULATOR ON
GATE OFF
V
= 72V
IN
V
= 14V
IN
6
4
2
80
0
50
-50 -25
0
25
50
75 100 125
0
10 20 30 40
60 70 80
0
20
40
60
80
TEMPERATURE (°C)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
UVLO THRESHOLD
vs. TEMPERATURE
GATE-DRIVE VOLTAGE
vs. INPUT VOLTAGE
SET THRESHOLD vs. TEMPERATURE
1.240
1.236
1.232
1.228
1.224
1.220
1.216
1.212
1.208
1.204
1.200
6.0
5.8
5.6
5.4
5.2
5.0
4.8
4.6
4.4
4.2
4.0
12
10
8
V
= V
IN
OUT
6
4
2
0
-50 -25
0
25
50
75 100 125
4
6
8
10 12 14 16 18 20 22 24
INPUT VOLTAGE (V)
-50 -25
0
25
50
75 100 125
TEMPERATURE (°C)
TEMPERATURE (°C)
4
_______________________________________________________________________________________
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
7/MAX6398
Typical Operating Characteristics (continued)
(V = 14V, C
= 4.7µF, I
= 0, unless otherwise noted.)
IN
REG
REG
GATE-TO-OUT CLAMP VOLTAGE
vs. TEMPERATURE
DROPOUT VOLTAGE
vs. REG LOAD CURRENT
REG OUTPUT VOLTAGE
vs. LOAD CURRENT AND TEMPERATURE
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
5.20
5.15
5.10
5.05
5.00
4.95
4.90
17.0
16.9
16.8
16.7
16.6
16.5
16.4
16.3
16.2
16.1
16.0
MAX6397L
MAX6397L
T
= +125°C
A
I
= 10mA
LOAD
I
= 50mA
LOAD
T
= +25°C
A
I
= 100mA
LOAD
T
= -40°C
A
-50 -25
0
25
50
75 100 125
0
20 40 60 80 100 120 140 160 180
REG LOAD CURRENT (mA)
-40 -25 -10
5
20 35 50 65 80 95 110 125
TEMPERATURE (°C)
TEMPERATURE (°C)
MAXIMUM REG OUTPUT VOLTAGE
vs. LOAD CURRENT AND TEMPERATURE
GATE-DRIVE VOLTAGE
vs. TEMPERATURE
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
0
-10
-20
-30
-40
-50
-60
-70
10.500
10.495
10.490
10.485
10.480
10.475
10.470
10.465
10.460
10.455
10.450
5.2
5.0
4.8
4.6
4.4
4.2
4.0
C
I
= 10µF
REG
= 10mA
T
= -40°C
A
REG
T
= +25°C
A
T
= +125°C
A
THERMAL
SHUTDOWN
10
100
1k
10k
100k
1M
10M
0
40 80 120 160 200 240 280 320 360 400
LOAD CURRENT (mA)
-50 -25
0
25
50
75 100 125
FREQUENCY (Hz)
TEMPERATURE (°C)
STARTUP WAVEFORM
STARTUP WAVEFORM FROM SHUTDOWN
(R
LOAD
= 100Ω, C = 10µF, C
= 10µF)
OUT
MAX6397-98 toc16
(C = 10µF, C
= 10µF)
IN
IN
OUT
MAX6397-98 toc17
R
= 100Ω
LOAD
V
IN
V
SHDN
10V/div
2V/div
V
V
GATE
GATE
10V/div
10V/div
V
OUT
V
OUT
10V/div
10V/div
I
I
OUT
OUT
200mA/div
200mA/div
4ms/div
400µs/div
_______________________________________________________________________________________
5
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
Typical Operating Characteristics (continued)
(V = 14V, C
= 4.7µF, I
= 0, unless otherwise noted.)
IN
REG
REG
VOLTAGE LIMIT FAULT
OVERVOLTAGE SWITCH FAULT
MAX6397-98 toc19
MAX6397-98 toc18
V
= 30V
OV
V
= 30V
V
IN
V
OV
IN
20V/div
20V/div
V
V
GATE
GATE
20V/div
20V/div
V
V
OUT
OUT
20V/div
20V/div
V
V
REG
REG
5V/div
5V/div
1ms/div
200µs/div
7/MAX6398
TRANSIENT RESPONSE
REG LOAD-TRANSIENT RESPONSE
MAX6397-98 toc20
MAX6397-98 toc21
C
= 10µF
REG
= 10mA
C
= 10µF
REG
I
REG
V
REG
V
IN
AC-COUPLED
500mV/div
10V/div
I
REG
V
REG
100mA/div
100mV/div
400µs/div
1ms/div
REGULATOR POK ASSERTION
REGULATOR STARTUP WAVEFORM
MAX6397-98 toc23
MAX6397-98 toc22
I
= 10mA
REG
V
REG
V
IN
2V/div
10V/div
0V
V
REG
2V/div
V
POK
2V/div
0V
0A
V
POK
I
2V/div
REG
200mA/div
I
= 0
REG
100µs/div
1ms/div
6
_______________________________________________________________________________________
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
7/MAX6398
Pin Description
PIN
NAME
FUNCTION
MAX6397
MAX6398
1
1
IN
Supply Voltage Input. Bypass with a minimum 10µF capacitor to GND.
Shutdown Input. Drive SHDN low to force GATE low, turning off the external n-channel
MOSFET. REG remains active when in shutdown mode. SHDN is internally pulled down
to GND with a 1µA source. Connect to IN for normal operation.
2
3
2
3
SHDN
Overvoltage Threshold Adjustment Input. Connect SET to an external resistor voltage-
divider network to OUT (overvoltage limiter) or IN (overvoltage switch) to adjust the
desired overvoltage limit threshold. Use SET to monitor a system input or output voltage.
SET
Open-Drain Output. POK remains low until REG exceeds 92.5% or 87.5% of REG
nominal output voltage. Connect to an external pullup resistor.
4
5
—
4
POK
GND
Ground
Gate-Drive Output. Connect GATE to the gate of an external n-channel MOSFET. GATE
is a charge pump with a 75µA pullup current to 10V (typ) above IN during normal
operation. GATE is quickly shorted to OUT during an overvoltage condition. GATE pulls
low when SHDN is low.
6
5
GATE
7
8
6
OUT
REG
EP
Output-Voltage-Sense Input. Connect to the source of the external n-channel MOSFET.
Regulator Output. Fixed 5.0V, 3.3V, 2.5V, or 1.8V output. REG sources up to 100mA.
Bypass with a minimum 4.7µF capacitor to GND.
—
—
—
Exposed Pad. Connect to ground plane.
The MAX6397/MAX6398 are configurable to operate as
Detailed Description
overvoltage protection switches or as closed-looped volt-
age limiters. In overvoltage protection switch mode, the
input voltage is monitored. When an overvoltage condi-
tion occurs at IN, GATE pulls low, disconnecting the load
from the power source, and then slowly enhances upon
removal of the overvoltage condition. In overvoltage
limit mode, the output voltage is monitored and the
MAX6397/MAX6398 regulate the source of the external
MOSFET at the adjusted overvoltage threshold, allowing
devices within the system to continue operating during an
overvoltage condition.
The MAX6397/MAX6398 are ultra-small, low-current,
high-voltage protection circuits for automotive applica-
tions that must survive load dump and high-voltage
transient conditions. These devices monitor the input/
output voltages and control an external n-channel
MOSFET to isolate the load or to regulate the output
voltage from overvoltage transient energy. The con-
troller allows system designers to size the external
MOSFET to their load current and board size.
The MAX6397/MAX6398 drive the MOSFET’s gate high
when the monitored input voltage is below the adjustable
overvoltage threshold. An internal charge-pump circuit
provides a 5V to 10V gate-to-source drive (see the
Typical Operating Characteristics) to ensure low input-to-
load voltage drops in normal operating modes. When the
input voltage rises above the user-adjusted overvoltage
threshold, GATE pulls to OUT, turning off
the MOSFET.
The MAX6397/MAX6398 undervoltage lockout (UVLO)
function disables the devices as long as the input
remains below the 5V (typ) UVLO turn-on threshold. The
MAX6397/MAX6398 have an active-low SHDN input to
turn off the external MOSFET, disconnecting the load and
reducing power consumption. After power is applied and
SHDN is driven above its logic-high voltage, there is a
100µs delay before GATE enhancement commences.
_______________________________________________________________________________________
7
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
Linear Regulator (MAX6397 Only)
The MAX6397 is available with 5.0V, 3.3V, 2.5V, and 1.8V
factory-set output voltages. Each regulator sources up to
100mA and includes a current limit of 230mA. The linear
regulator operates in an always-on condition regardless
IN
THERMAL
PROTECTION
of the SHDN logic. For fully specified operation, V must
IN
be greater than 6.5V for the MAX6397L/M (5V regulator
output). The actual output current may be limited by the
operating condition and package power dissipation.
UVLO
10V
CHARGE
PUMP
Power-OK Output
POK is an open-drain output that goes low when REG
falls to 92.5% or 87.5% (see the Selector Guide) of its
nominal output voltage. To obtain a logic-level output,
connect a pullup resistor from POK to REG or another
system voltage. Use a resistor in the 100kΩ range to
minimize current consumption. POK provides a valid
5V
GATE
SET
OUT
logic-output level down to V = 1.5V.
IN
1.23V
SHDN
GATE Voltage
7/MAX6398
The MAX6397/MAX6398 use a high-efficiency charge
pump to generate the GATE voltage. Upon V exceed-
IN
REG
LINEAR
REGULATOR
ing the 5V (typ) UVLO threshold, GATE enhances 10V
above IN (for V ≥14V) with a 75µA pullup current. An
IN
overvoltage condition occurs when the voltage at SET
pulls above its 1.215V threshold. When the threshold is
crossed, GATE falls to OUT within 100ns with a 100mA
(typ) pulldown current. The MAX6397/MAX6398 include
an internal clamp to OUT that ensures GATE is limited
to 18V (max) above OUT to prevent gate-to-source
damage to the external FET.
MAX6397
MAX6398
POK
GND
V
POK_TH
MAX6397 ONLY
The GATE cycle during overvoltage limit and overvolt-
age switch modes are quite similar but have distinct
characteristics. In overvoltage switch mode (Figure 2a),
GATE is enhanced to V + 10V while the monitored IN
IN
Figure 1. Functional Diagram
voltage remains below the overvoltage fault threshold
(SET < 1.215V). When an overvoltage fault occurs (SET
≥ 1.215V), GATE is pulled one diode below OUT, turn-
ing off the external FET and disconnecting the load
from the input. GATE remains low (FET off) as long as
The MAX6397 integrates a high-input-voltage, low-qui-
escent-current linear regulator in addition to an over-
voltage protector circuit. The linear regulator remains
enabled at all times to power low-current “always-on”
applications (independent of the state of the external
MOSFET). The regulator is offered with several stan-
dard output voltage options (5V, 3.3V, 2.5V, or 1.8V).
An open-drain power-good output notifies the system if
the regulator output falls to 92.5% or 87.5% of its nomi-
nal voltage. The MAX6397’s REG output operates inde-
pendently of the SHDN logic input.
V
is above the overvoltage fault threshold. As V falls
IN
IN
back below the overvoltage fault threshold (-5% hys-
teresis) GATE is again enhanced to V + 10V.
IN
In overvoltage limit mode (Figure 2b), GATE is enhanced
to V + 10V. While the monitored OUT voltage remains
IN
below the overvoltage fault threshold (SET < 1.215V).
When an overvoltage fault occurs (SET ≥ 1.215V),
GATE is pulled low one diode drop below OUT until
OUT drops 5% below the overvoltage fault threshold.
GATE is then turned back on until OUT again reaches
the overvoltage fault threshold and GATE is again
turned off.
The MAX6397/MAX6398 include internal thermal-shut-
down protection, disabling the external MOSFET and
linear regulator if the chip reaches overtemperature
conditions.
8
_______________________________________________________________________________________
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
7/MAX6398
V
IN
10V/div
GATE
V
BATT
IN
OUT
R1
R2
V
MAX6397
MAX6398
GATE
10V/div
SET
V
OUT
GND
10V/div
10ms/div
Figure 3. Overvoltage Switch Protection Configuration
Figure 2a. MAX6397/MAX6398 GATE Waveform During Over-
voltage Switch Mode
Overvoltage Monitoring
When operating in overvoltage mode, the MAX6397/
MAX6398 feedback path (Figure 3) consists of IN,
SET’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, pulling GATE to OUT
V
IN
10V/div
V
GATE
within t
and disconnecting the power source from
10V/div
OV
the load. When IN decreases below the adjusted over-
voltage threshold, the MAX6397/MAX6398 slowly
enhance GATE above OUT, reconnecting the load to
the power source.
V
OUT
10V/div
Overvoltage Limiter
When operating in overvoltage limiter mode, the
MAX6397/MAX6398 feedback path (Figure 4) consists
of OUT, SET’s internal comparator, the internal gate
charge pump and the external n-channel MOSFET,
which results in the external MOSFET operating as a
voltage regulator.
4ms/div
Figure 2b. MAX6397/MAX6398 GATE Waveform During Over-
voltage Limit Mode
GATE cycles on-off-on-off-on in a sawtooth waveform
until OUT remains below the overvoltage fault threshold
and GATE remains constantly on (V + 10V). The over-
IN
voltage limiter’s sawtooth GATE output operates the
MOSFET in a switched-linear mode while the input volt-
age 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).
During normal operation, GATE is enhanced 10V above
OUT. The external MOSFET source voltage is monitored
through a resistor-divider between OUT and SET. When
OUT rises above the adjusted overvoltage threshold, an
internal comparator sinks the charge-pump current, dis-
charging the external GATE, regulating OUT at the set
overvoltage threshold. OUT remains active during the
overvoltage transients and the MOSFET continues to con-
duct during the overvoltage event, operating in switched-
linear mode.
GATE goes high when the following startup conditions
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.
_______________________________________________________________________________________
9
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
C
OUT
V
PEAK
GATE
V
IN
OUT
SET
BATT
R1
R2
MAX6397
MAX6398
t
> 5ms
RISE
V
BATT
GND
100ms
200ms
300ms
400ms
Figure 4. Overvoltage Limiter Protection Switch Configuration
Figure 5. Load Dump Voltage Profile
As the transient begins decreasing, OUT fall time will
depend on the MOSFET’s GATE charge, the internal
charge-pump current, the output load, and the tank
capacitor at OUT.
characteristics of the charging system (Figure 5).
These transients are capable of destroying semicon-
ductors on the first ‘fault event.’
7/MAX6398
Setting Overvoltage Thresholds
SET provides an accurate means to set the overvoltage
level for the MAX6397/MAX6398. Use a resistor-divider to
set the desired overvoltage condition (Figure 6). SET has
a rising 1.215V threshold with a 5% falling hysteresis.
For fast-rising transients and very large-sized MOSFETs,
add an additional external 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 MOSFETs’ drain-to-gate capaci-
Begin by selecting the total end-to-end resistance,
tance. For a 6000pF C , a 0.1µF capacitor at GATE will
gd
R
= R1 + R2. Choose R
to yield a total cur-
TOTAL
TOTAL
reduce the impact of the fast-rising V input.
IN
rent equivalent to a minimum 100 x I
(SET’s input
SET
Caution must be exercised when operating the
MAX6397/MAX6398 in voltage-limiting mode for long
durations. If the V is a DC voltage greater than the
IN
MOSFET’s maximum gate voltage, the FET will dissipate
power continuously. To prevent damage to the external
MOSFET, proper heatsinking should be implemented.
bias current) at the desired overvoltage threshold.
For example:
With an overvoltage threshold set to 20V:
R
< 20V/(100 x I
)
TOTAL
SET
where I
is SET’s 50nA input bias current.
SET
Applications Information
R
< 4MΩ
TOTAL
Use the following formula to calculate R2:
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. Power in the alternator (essen-
tially an inductor) flows into the distributed power sys-
tem 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
R
TOTAL
R2 = V
×
TH
V
OV
where V is the 1.215V SET rising threshold and V
TH
is the overvoltage threshold.
OV
R2 = 243kΩ, use a 240kΩ standard resistor.
R
= R2 + R1, where R1 = 3.76MΩ.
TOTAL
Use a 3.79MΩ standard resistor.
A lower value for total resistance dissipates more
power but provides slightly better accuracy.
10 ______________________________________________________________________________________
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
7/MAX6398
GATE
GATE
IN
IN
IN
OUT
SET
IN
OUT
R1
R2
R1
R2
MAX6397
MAX6398
MAX6397
MAX6398
SET
GND
GND
Figure 6. Setting the MAX6397/MAX6398 Overvoltage Threshold
Q1
IN
IN
GATE
GATE
V
V
BATT
LOAD
LOAD
BATT
MAX6397
MAX6398
MAX6397
MAX6398
OUT
OUT
GND
GND
(a)
(b)
Figure 7. Reverse Battery Protection Using a Diode or p-Channel MOSFET
the drain voltage. When the source voltage exceeds
Q1’s threshold voltage, Q1 turns on. Once the FET is
on, the battery is fully connected to the system and can
deliver power to the device and the load.
Reverse-Battery Protection
Use a diode or p-channel MOSFET to protect the
MAX6397/MAX6398 during a reverse-battery insertion
(Figures 7a, 7b). Low p-channel MOSFET on-resistance
of 30mΩ or less yields a forward-voltage drop of only a
few millivolts (versus hundreds of millivolts for a diode,
Figure 7a) thus improving efficiency.
An incorrectly inserted battery reverse-biases the FET’s
body diode. The gate remains at the ground potential.
The FET remains off and disconnects the reversed bat-
tery from the system. The zener diode and resistor com-
bination prevent damage to the p-channel MOSFET
during an overvoltage condition.
Connecting a positive battery voltage to the drain of Q1
(Figure 7b) produces forward bias in its body diode,
which clamps the source voltage one diode drop below
______________________________________________________________________________________ 11
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
V
BATT
1kΩ
IN
GATE
C
GATE
IN
C
V
OUT
LOAD
BATT
GATE
60V
TVS
MAX6397
MAX6398
LOAD
MAX6397
MAX6398
OUT
GND
OUT
GND
7/MAX6398
Figure 8. MAX6397/MAX6398 Controlling GATE Inrush Current
Figure 9. Protecting the MAX6397/MAX6398 Input from High-
Voltage Transients
where I
is GATE’s 75µA sourcing current, I
is
REG Capacitor Selection for Stability
For stable operation over the full temperature range and
with load currents up to 100mA, use ceramic capacitor
values greater than 4.7µF. Large output capacitors help
reduce noise, improve load-transient response, and
power-supply rejection at REG. Note that some ceramic
dielectrics exhibit large capacitance and ESR variation
with temperature. At lower temperatures, it may be nec-
essary to increase capacitance.
GATE
LOAD
is the output
the load current at startup, and C
capacitor.
OUT
Input Transients Clamping
When the external MOSFET is turned off during an over-
voltage occurrence, stray inductance in the power path
may cause voltage ringing exceeding the MAX6397/
MAX6398 absolute maximum input (IN) supply rating.
The following techniques are recommended to reduce
the effect of transients:
Under normal conditions, use a 10µF capacitor at IN.
Larger input capacitor values and lower ESR provide bet-
ter supply-noise rejection and line-transient response.
•
Minimize stray inductance in the power path using
wide traces, and minimize loop area including the
power traces and the return ground path.
Inrush/Slew-Rate Control
Inrush current control can be implemented by placing a
capacitor at GATE (Figure 8) 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 formula:
•
Add a zener diode or transient voltage suppressor
(TVS) rated below the IN absolute maximum rating
(Figure 9).
Add a resistor in series with IN to limit transient current
going into the input for the MAX6398 only.
C
OUT
I
=
× I
+ I
INRUSH
GATE LOAD
C
GATE
12 ______________________________________________________________________________________
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
7/MAX6398
V
MAX
V
OV
V
Q1
V
BATT
V
BATT
+
-
I
LOAD
GATE
OUT
t
2
IN
GATE
OUT
60V
TVS
LOAD
t
1
t
3
MAX6397
MAX6398
SET
t
OVP
GND
Figure 11. MAX6397/MAX6398 Timing Diagram
same thermal island. Good thermal contact between the
MAX6397/MAX6398 and the external nFET is essential
for the thermal-shutdown feature to operate effectively.
Place the nFET as close as possible to OUT.
Figure 10. Power Dissipated Across MOSFETs During an
Overvoltage Fault (Overvoltage Limiter Mode)
When the junction temperature exceeds T = +150°C,
J
MOSFET Selection
the thermal sensor signals the shutdown logic, turning off
REG’s internal pass transistor and the GATE output,
allowing the device to cool. The thermal sensor turns
the pass transistor and GATE on again after the IC’s
junction temperature cools by 20°C. Thermal-overload
protection is designed to protect the MAX6397/
MAX6398 and the external MOSFET in the event of cur-
rent-limit fault conditions. For continuous operation, do
not exceed the absolute maximum junction-tempera-
Select external MOSFETs according to the application
current level. The MOSFET’s on-resistance (R
)
DS(ON)
should be chosen low enough to have 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 MAX6397/
MAX6398 in overvoltage limit mode.
During normal operation, the external MOSFETs dissipate
little power. The power dissipated in normal operation is:
ture rating of T = +150°C.
J
P
Q1
= I
2 x R
LOAD DS(ON).
Thermal Shutdown
Overvoltage Limiter Mode
When operating the MAX6397/MAX6398 in overvoltage
limit mode for a prolonged period of time, a thermal
shutdown is possible due to device self-heating. The
thermal shutdown is dependent on a number of differ-
ent factors:
The most power dissipation will occur during a pro-
longed overvoltage event when operating the
MAX6397/MAX6398 in voltage limiter mode, resulting in
high power dissipated in Q1 (Figure 10) where the
power dissipated across Q1 is:
P
Q1
= V x I
Q1 LOAD
where V
is the voltage across the MOSFET’s drain
Q1
•
•
•
•
•
•
The device’s ambient temperature (T )
A
and source.
The output capacitor (C
)
OUT
Thermal Shutdown
The output load current (I
)
OUT
The MAX6397/MAX6398 thermal-shutdown feature shuts
off the linear regulator output, REG, and GATE if it
exceeds the maximum allowable thermal dissipation.
Thermal shutdown also monitors the PC board tempera-
ture of the external nFET when the devices sit on the
The overvoltage threshold limit (V
)
OV
The overvoltage waveform period (t
)
OVP
The power dissipated across the package (P
)
DISS
______________________________________________________________________________________ 13
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
During ∆t2, C
loses charge through the output load.
OUT
The voltage across C
(∆V2) decreases until the
OUT
180
170
I
= 0
OUT
A
THERMAL SHUTDOWN
MOSFET reaches its V
approximated using the following formula:
threshold and can be
GS(TH)
T = +125°C
CGATE = 0
160
150
140
∆t2
∆V2 = I
OUT
C
OUT
CGATE = 10nF
Once the MOSFET V
(
) is obtained, the slope of the
output voltage rise is determined by the MOSFET Q
GS TH
CGATE = InF
G
charge through the internal charge pump with respect
to the drain potential. The time for the OUT voltage to
rise again to the overvoltage threshold can be approxi-
mated using the following formula:
130
120
CGATE = ADDITIONAL CAPACITANCE
FROM GATE TO GND
1
10
100
1000
OUTPUT CAPACITANCE (µF)
Q
∆V
OUT
I
GATE
GD
GS _QGD
∆t3 ≅
×
V
Figure 12. Junction Temperature vs. C
OUT
where ∆V
= ( V x 0.05) + ∆V2.
OV
When OUT exceeds the adjusted overvoltage threshold,
an internal GATE pulldown current is enabled until OUT
drops by 5%. The capacitance at OUT is discharged by
the internal current sink and the external OUT load cur-
rent. The discharge time (∆t1) is approximately:
OUT
7/MAX6398
The total period of the overvoltage waveform can be
summed up as follows:
t
= ∆t1 + ∆t2 + ∆t3
OVP
The MAX6397/MAX6398 dissipate the most power dur-
ing an overvoltage event when I = 0 (C is dis-
charged only by the internal current sink). The maximum
power dissipation can be approximated using the follow-
ing equation:
V
× 0.05
OUT
OUT
OV
∆t1 = C
OUT
I
+ I
OUT
GATEPD
where V
is the adjusted overvoltage threshold, I
OUT
OV
is the external load current and I
is the GATE’s
GATEPD
∆t1
internal 100mA (typ) pulldown current.
P
= V
× 0.975 × I
×
DISS
OV
GATEPD
∆t
When OUT falls 5% below the overvoltage threshold
point, the internal current sink is disabled and the
MAX6397/MAX6398’s internal charge pump begins
recharging the external GATE voltage. The OUT volt-
age continues to drop due to the external OUT load
current until the MOSFET gate is recharged. The time
needed to recharge GATE and re-enhance the external
nFET is approximately:
OVP
The die temperature (T ) increase is related to θ
J
JC
(8.3°C/W and 8.5°C/W for the MAX6397 and MAX6398,
respectively) of the package when mounted correctly
with a strong thermal contact to the circuit board. The
MAX6397/MAX6398 thermal shutdown is governed by
the equation:
T = T + P
(typical thermal-shutdown temperature)
x (θ
+ θ
< 170°C
)
CA
J
A
DISS
JC
V
+ V
F
GS(TH)
∆t2 = C
ISS
For the MAX6397, the power dissipation of the internal
linear regulator must be added to the overvoltage pro-
tection circuit power dissipation to calculate the die
temperature. The linear regulator power dissipation is
calculated using the following equation:
I
GATE
where C
is the MOSFET’s input capacitance, V
GS(TH)
ISS
is the MOSFET’s gate-to-source threshold voltage, V is
F
the internal clamp diode forward voltage (V = 1.5V typ),
F
and I
is the MAX6397/MAX6398 charge-pump cur-
GATE
P
REG
= (V – V
) (I
REG REG
)
IN
rent (75µA typ).
For example, using an IRFR3410 100V n-channel
MOSFET, Figure 12 illustrates the junction temperature
vs. output capacitor with I
= 0, T = +125°C,
A
OUT
= 75mA, and I
V
OV
< 16V,V = 1.5V, I
=
F
GATE
GATEPD
100mA. Figure 12 shows the relationship between output
capacitance versus die temperature for the conditions
listed above.
14 ______________________________________________________________________________________
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
7/MAX6398
An additional capacitor can be added to GATE and
OUTPUT Current Calculation
The MAX6397 high input voltage (+72V max) provides up
to 100mA of output current at REG. Package power dissi-
pation limits the amount of output current available for a
given input/output voltage and ambient temperature.
Figure 13 depicts the maximum power dissipation curve
for the MAX6397. The graph assumes that the exposed
metal pad of the MAX6397 package is soldered to 1in2 of
PC board copper. Use Figure 11 to determine the allow-
able package dissipation for a given ambient tempera-
ture. Alternately, use the following formula to calculate the
allowable package dissipation:
GND to shift the curves as this increases ∆t1. These val-
ues are used for illustration only. Customers must verify
worst-case conditons for their specific application.
2.0
1.455W
1.8
1.6
DERATE 18.2mW/°C
ABOVE +70°C
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
P
DISS
= 1.455W for T ≤ +70°C
A
Maximum power dissipation =
1.455 - 0.0182 (T - 70°C) for +70°C ≤ T ≤ +125°C
A
A
where, 0.0182 W/°C is the MAX6397 package thermal
derating.
After determining the allowable package dissipation,
calculate the maximum output current using the follow-
ing formula:
0
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
Figure 13. Maximum Power Dissipation vs. Temperature
P
D
ISS
− V
I
=
≤ 100mA
OUT(MAX)
V
IN
REG
Typical Application Circuit
DC-DC
CONVERTER
IN
OUT
µC
GND
GATE
12V IN
IN
OUT
SET
REG
POK
MAX6397
V
CC
SHDN
GND
RESET
GPIO
ALWAYS-ON
µC
______________________________________________________________________________________ 15
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
Typical Operating Circuit
DC-DC
DC-DC
CONVERTER
CONVERTER
C
OUT
C
OUT
GATE
GATE
V
BATT
V
BATT
IN
OUT
SET
IN
OUT
REG
R1
R2
R1
R2
MAX6397
MAX6398
MAX6397
MAX6398
REG
SET
GND
GND
7/MAX6398
OVERVOLTAGE LIMITER CONTROLLER
OVERVOLTAGE SWITCH CONTROLLER
Selector Guide
Pin Configurations (continued)
REG OUTPUT POK ASSERTION
VOLTAGE (V) THRESHOLD (%) MARK
TOP
TOP VIEW
PART
OUT
6
GATE
5
GND
4
MAX6397LATA
MAX6397MATA
MAX6397SATA
MAX6397TATA
MAX6397YATA
MAX6397ZATA
MAX6397VATA
MAX6397WATA
MAX6398ATT
5.0
5.0
3.3
3.3
2.5
2.5
1.8
1.8
—
92.5
87.5
87.5
92.5
87.5
92.5
87.5
92.5
—
ANN
ANO
ANQ
ANP
ANK
ANJ
ANM
ANL
AJD
*EP
MAX6398
1
2
3
IN
SHDN SET
TDFN
*EXPOSED PAD. CONNECT TO GND.
16 ______________________________________________________________________________________
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
7/MAX6398
Package Information
Chip Information
For the latest package outline information and land patterns, go
TRANSISTOR COUNT: 590
PROCESS: BiCMOS
to www.maxim-ic.com/packages.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
6 TDFN
T633-2
21-0137
21-0137
8 TDFN
T833-2
______________________________________________________________________________________ 17
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
DESCRIPTION
0
3
4
5
5/05
1/07
3/07
1/09
Initial release
—
1, 14, 15, 17
1, 3, 18
3
Changed formula and updated Figure 13 caption title.
Updated Electrical Characteristics table.
Updated Electrical Characteristics table.
7/MAX6398
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.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2009 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.
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