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19-3668; Rev 3; 1/07
Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V
General Description
The MAX6397/MAX6398 are small, high-voltage overvoltage protection circuits. These devices disconnect the output load or limit the output voltage during an input overvoltage condition. These devices are ideal for applications that must survive high-voltage transients such as those found in automotive and industrial applications. 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 useradjustable 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. When the input voltage exceeds the overvoltage threshold, 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. 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 37A of quiescent current. 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. The MAX6397/MAX6398 include internal thermal-shutdown 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 -40C to +125C.
Features
5.5V to 72V Wide Supply Voltage Range Overvoltage Protection Controllers Allow User to Size External n-Channel MOSFETs Internal Charge-Pump Circuit Ensures MOSFET Gate-to-Source Enhancement for Low RDS(ON) Performance Disconnect or Limit Output from Input During Overvoltage Conditions Adjustable Overvoltage Threshold Thermal-Shutdown Protection Always-On, Low-Current (37A) Linear Regulator Sources Up to 100mA (MAX6397) Fully Specified from -40C to +125C (TJ) Small, Thermally Enhanced 3mm x 3mm TDFN Package
MAX6397/MAX6398
Ordering Information
PART TEMP RANGE PIN-PACKAGE PKG CODE T833-2 T633-2
MAX6397_ATA-T* -40C to +125C 8 TDFN-EP** MAX6398ATT-T* -40C to +125C 6 TDFN-EP**
*Replace "-T" with "+T" for lead-free 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. Selector Guide and Typical Operating Circuit appear at end of data sheet.
Pin Configurations
TOP VIEW
REG 8 *EP OUT 7 GATE GND 6 5
Applications
Automotive Industrial FireWire(R) Notebook Computers Wall Cube Power Devices
MAX6397
1 IN
2 SHDN
3 SET
4 POK
FireWire is a registered trademark of Apple Computer, Inc.
TDFN
*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/Dallas 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 MAX6397/MAX6398
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: IN, REG...............................................................................350mA All Remaining Pins ...................................................................50mA Continuous Power Dissipation (TA = +70C) 6-Pin TDFN (derate 18.2mW/C above +70C) .............1455mW 8-Pin TDFN (derate 18.2mW/C above +70C) .............1455mW Operating Temperature Range (TA) ......................-40C to +125C Junction Temperature ...........................................................+150C Storage Temperature Range .................................-65C to +150C Lead Temperature ................................................................+300C
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 = 6000pF, CREG = 4.7F, TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = TJ = +25C.) (Note 1)
PARAMETER Supply Voltage Range SYMBOL VIN SHDN = high, no load (MAX6397) Input Supply Current SHDN = high, (MAX6398) SHDN = low, no load (MAX6397) SHDN = low, (MAX6398) IN Undervoltage Lockout IN Undervoltage Lockout Hysteresis SET Threshold Voltage SET Threshold Hysteresis SET Input Current Startup Response Time GATE Rise Time SET to GATE Propagation Delay tOV VTH VHYST ISET tSTART SHDN rising (Note 2) GATE rising from GND to VOUT + 8V, CGATE = 6000pF, OUT = GND SET rising from VTH - 100mV to VTH + 100mV VOUT = VIN = 6V, RGATE to IN = 1M GATE Output High Voltage VOH VOUT = VIN; VIN 14V, RGATE to IN = 1M GATE Output Low Voltage GATE Charge-Pump Current GATE to OUT Clamp Voltage SHDN Logic-High Input Voltage SHDN Logic-Low Input Voltage SHDN Input Pulldown Current Thermal Shutdown Thermal Shutdown Hysteresis REGULATOR (MAX6397) Ground Current IGND SHDN = GND IREG = 1mA IREG = 100mA 40 60 48 A VOL IGATE VCLMP VIH VIL VSHDN = 2V, SHDN is internally pulled down to GND (Note 3) 1 +150 20 GATE sinking 20mA, VOUT = GND GATE = GND 13 1.4 0.4 A C C 75 18 VIN + 3.8V VIN + 8.5V VIN + 4.2V VIN + 9.2V -50 100 1 0.75 VIN + 4.6V V VIN + 11.5V 0.38 V A V VIN rising, enables GATE VIN falling, disables GATE With respect to GND 1.181 4.66 CONDITIONS MIN 5.5 118 104 37 11 5 175 1.215 4 +50 1.248 TYP MAX 72 140 130 45 20 5.50 V mV V % nA s ms s A UNITS V
2
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Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 14V; CGATE = 6000pF, CREG = 4.7F, TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = TJ = +25C.) (Note 1)
PARAMETER SYMBOL MAX6397L/M MAX6397S/T REG Output Voltage (VIN VREG + 1.8V) VREG MAX6397Y/Z MAX6397V/W Dropout Voltage (Note 4) Current Limit Overvoltage-Protection Threshold Overvoltage-Protection Sink Current Line Regulation (Note 5) VOVP IOVP VREG / VREG VREG / IREG tSTART VREG = 1.1 x VREG (nominal) 6.5V VIN 72V, IREG = 10mA, VREG = 5V 5.5V VIN 72V, IREG = 1mA, VREG = 5V 5.5V VIN 72V, IREG = 100mA, VREG = 5V 1mA IREG 100mA, VREG = 5V IREG = 10mA, f = 100Hz, 0.5VP-P RREG = 500, VREG = 5V, CREG = 4.7F L M T POK Assertion Threshold (MAX6397 Only) VPOK_TH S Z Y W V REG to POK Delay POK Leakage Current POK Output Low Voltage VOL VREG rising or falling VPOK = 5V VIN 1.5V, ISINK = 1.6mA, POK asserted 4.500 4.230 2.966 2.805 2.250 2.125 1.590 1.524 55 180 4.67 4.375 3.053 2.892 2.304 2.188 1.653 1.575 35 100 0.3 4.780 4.500 3.140 2.970 2.375 2.250 1.696 1.625 s nA V V 1.5 0.8 mV/mA dB s VDO CONDITIONS IREG = 1mA 1mA < IREG < 100mA IREG = 1mA 1mA < IREG < 100mA IREG = 1mA 1mA < IREG < 100mA IREG = 1mA 1mA < IREG < 100mA MIN 4.925 4.85 3.243 3.201 2.456 2.41 1.760 1.715 1.8 2.5 3.3 TYP 5 MAX 5.120 5.15 3.360 3. 360 2.542 2.55 1.837 1.837 0.12 1.2 150 105 15 0.22 0.05 mV/mA 300 mA % of VREG mA mV/V V UNITS
5.5V VIN 72V, IREG = 1mA, VREG = 5V 5.5V VIN 72V, IREG = 100mA, VREG = 5V VIN = 14V
Load Regulation Power-Supply Rejection Ratio Startup Response Time
Note 1: Specifications to -40C are guaranteed by design and not production tested. Note 2: The MAX6397/MAX6398 power up with the external FET in off mode (VGATE = GND). The external FET turns on tSTART after the 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 VIN - VREG when VREG is 2% below the value of VREG for VIN = VREG (nominal) + 2V. Note 5: Operations beyond the thermal dissipation limit may permanently damage the device.
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3
Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
Typical Operating Characteristics
(VIN = 14V, CREG = 4.7F, IREG = 0, unless otherwise noted.)
SUPPLY CURRENT vs. INPUT VOLTAGE
MAX6397-98 toc01
SUPPLY CURRENT vs. TEMPERATURE
MAX6397-98 toc02
SUPPLY CURRENT vs. INPUT VOLTAGE
110 SUPPLY CURRENT (A) 100 90 80 70 60 50 40 MAX6398 GATE ON
MAX6397-98 toc03
160 140 SUPPLY CURRENT (A) 120 100 80 60 40 0 10 20 30 40 50 60 70 MAX6397 GATE ON
180 170 160 SUPPLY CURRENT (A) 150 140 130 120 110 100 90 80
MAX6397
120
VIN = 72V
VIN = 14V
80
-50
-25
0
25
50
75
100
125
0
20
40 INPUT VOLTAGE (V)
60
80
INPUT VOLTAGE (V)
TEMPERATURE (C)
SUPPLY CURRENT vs. TEMPERATURE
MAX6397-98 toc04
SHUTDOWN SUPPLY CURRENT vs. INPUT VOLTAGE (MAX6397)
MAX6397-98 toc05
SHUTDOWN SUPPLY CURRENT vs. INPUT VOLTAGE
18 16 SUPPLY CURRENT (A) 14 12 10 8 6 4 2 MAX6398 GATE OFF
MAX6397-98 toc06
140 130 SUPPLY CURRENT (A) 120 110 100 90 80 -50 -25 0 25 50 75 100 VIN = 14V MAX6398 GATE ON
50 45 SUPPLY CURRENT (A) 40 35 30 25 20 REGULATOR ON GATE OFF
20
VIN = 72V
125
0
10
20
30
40
50
0 60 70 80 0 20 40 INPUT VOLTAGE (V) 60 80
TEMPERATURE (C)
INPUT VOLTAGE (V)
GATE-DRIVE VOLTAGE vs. INPUT VOLTAGE
MAX6397-98 toc07
UVLO THRESHOLD vs. TEMPERATURE
MAX6397-98 toc08
SET THRESHOLD vs. TEMPERATURE
1.236 1.232 SET THRESHOLD (V) 1.228 1.224 1.220 1.216 1.212 1.208 1.204 1.200
MAX6397-98 toc09
12 VOUT = VIN 10 VGATE - VOUT (V) 8 6 4 2 0 4 6 8
6.0 5.8 5.6 5.4 VUVLO (V) 5.2 5.0 4.8 4.6 4.4 4.2 4.0
1.240
10 12 14 16 18 20 22 24 INPUT VOLTAGE (V)
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100
125
TEMPERATURE (C)
TEMPERATURE (C)
4
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Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
Typical Operating Characteristics (continued)
(VIN = 14V, CREG = 4.7F, IREG = 0, unless otherwise noted.)
GATE-TO-OUT CLAMP VOLTAGE vs. TEMPERATURE
MAX6397-98 toc10
DROPOUT VOLTAGE vs. REG LOAD CURRENT
MAX6397-98 toc11
REG OUTPUT VOLTAGE vs. LOAD CURRENT AND TEMPERATURE
MAX6397L 5.15 REG OUTPUT VOLTAGE (V) 5.10 ILOAD = 10mA 5.05 5.00 4.95 4.90 ILOAD = 100mA ILOAD = 50mA
MAX6397-98 toc12
17.0 GATE-TO-OUT CLAMP VOLTAGE (V) 16.9 16.8 16.7 16.6 16.5 16.4 16.3 16.2 16.1 16.0 -50 -25 0 25 50 75 100
2.0 1.8 1.6 DROPOUT VOLTAGE (V) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 TA = +25C TA = -40C TA = +125C MAX6397L
5.20
125
0
20
40
60
80 100 120 140 160 180
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
TEMPERATURE (C)
REG LOAD CURRENT (mA)
MAXIMUM REG OUTPUT VOLTAGE vs. LOAD CURRENT AND TEMPERATURE
MAX6397-98 toc13
GATE-DRIVE VOLTAGE vs. TEMPERATURE
MAX6397-98 toc14
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
CREG = 10F IREG = 10mA
MAX6397-98 toc15
5.2 TA = -40C 5.0 REG OUTPUT VOLTAGE (V) 4.8 TA = +25C 4.6 4.4 4.2 4.0 0 TA = +125C THERMAL SHUTDOWN
10.500 10.495 GATE-DRIVE VOLTAGE (V) 10.490 10.485
0 -10 -20 PSRR (dB) -30 -40 -50 -60 -70
10.480 10.475 10.470 10.465 10.460 10.455 10.450
40 80 120 160 200 240 280 320 360 400 LOAD CURRENT (mA)
-50
-25
0
25
50
75
100
125
10
100
1k
10k
100k
1M
10M
TEMPERATURE (C)
FREQUENCY (Hz)
STARTUP WAVEFORM (RLOAD = 100, CIN = 10F, COUT = 10F)
MAX6397-98 toc16
STARTUP WAVEFORM FROM SHUTDOWN (CIN = 10F, COUT = 10F)
MAX6397-98 toc17
RLOAD = 100 VIN 10V/div VSHDN 2V/div
VGATE 10V/div
VGATE 10V/div
VOUT 10V/div IOUT 200mA/div 4ms/div 400s/div
VOUT 10V/div IOUT 200mA/div
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5
Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
Typical Operating Characteristics (continued)
(VIN = 14V, CREG = 4.7F, IREG = 0, unless otherwise noted.)
OVERVOLTAGE SWITCH FAULT
MAX6397-98 toc18
VOLTAGE LIMIT FAULT
MAX6397-98 toc19
VOV = 30V
VIN 20V/div
VOV = 30V
VIN 20V/div
VGATE 20V/div
VGATE 20V/div
VOUT 20V/div VREG 5V/div 200s/div 1ms/div
VOUT 20V/div VREG 5V/div
TRANSIENT RESPONSE
MAX6397-98 toc20
REG LOAD-TRANSIENT RESPONSE
MAX6397-98 toc21
CREG = 10F IREG = 10mA VIN 10V/div
CREG = 10F VREG AC-COUPLED 500mV/div
VREG 100mV/div
IREG 100mA/div
400s/div
1ms/div
REGULATOR STARTUP WAVEFORM
MAX6397-98 toc22
REGULATOR POK ASSERTION
MAX6397-98 toc23
IREG = 10mA VIN 10V/div 0V VREG 2V/div VPOK 2V/div 0V IREG = 0 100s/div IREG 200mA/div VREG 2V/div
VPOK 2V/div
0A 1ms/div
6
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Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
Pin Description
PIN MAX6397 1 2 MAX6398 1 2 NAME IN SHDN FUNCTION Supply Voltage Input. Bypass with a minimum 10F 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 1A source. Connect to IN for normal operation. Overvoltage Threshold Adjustment Input. Connect SET to an external resistor voltagedivider 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. 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. Ground Gate-Drive Output. Connect GATE to the gate of an external n-channel MOSFET. GATE is a charge pump with a 75A 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. 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 4.7F capacitor to GND. Exposed Pad. Connect to ground plane.
3
3
SET
4 5
-- 4
POK GND
6
5
GATE
7 8 EP
6 -- EP
OUT REG --
Detailed Description
The MAX6397/MAX6398 are ultra-small, low-current, high-voltage protection circuits for automotive applications 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 controller 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-toload 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 are configurable to operate as overvoltage protection switches or as closed-looped voltage limiters. In overvoltage protection switch mode, the input voltage is monitored. When an overvoltage condition 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 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 100s delay before GATE enhancement commences.
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Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
Linear Regulator (MAX6397 Only)
IN THERMAL PROTECTION
UVLO 10V CHARGE PUMP GATE
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 of the SHDN logic. For fully specified operation, VIN must 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.
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 100k range to minimize current consumption. POK provides a valid logic-output level down to VIN = 1.5V.
5V
SET
OUT 1.23V SHDN
GATE Voltage
The MAX6397/MAX6398 use a high-efficiency charge pump to generate the GATE voltage. Upon VIN exceeding the 5V (typ) UVLO threshold, GATE enhances 10V above IN (for VIN 14V) with a 75A pullup current. An 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. The GATE cycle during overvoltage limit and overvoltage switch modes are quite similar but have distinct characteristics. In overvoltage switch mode (Figure 2a), GATE is enhanced to VIN + 10V while the monitored IN 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, turning off the external FET and disconnecting the load from the input. GATE remains low (FET off) as long as VIN is above the overvoltage fault threshold. As VIN falls back below the overvoltage fault threshold (-5% hysteresis) GATE is again enhanced to VIN + 10V. In overvoltage limit mode (Figure 2b), GATE is enhanced to VIN + 10V. While the monitored OUT voltage remains 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.
LINEAR REGULATOR
REG
MAX6397 MAX6398
POK
VPOK_TH MAX6397 ONLY
GND
Figure 1. Functional Diagram
The MAX6397 integrates a high-input-voltage, low-quiescent-current linear regulator in addition to an overvoltage 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 standard 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 nominal voltage. The MAX6397's REG output operates independently of the SHDN logic input. The MAX6397/MAX6398 include internal thermal-shutdown protection, disabling the external MOSFET and linear regulator if the chip reaches overtemperature conditions.
8
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Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
VIN 10V/div GATE VBATT R1 VGATE 10V/div IN OUT
MAX6397 SET MAX6398
R2 GND
VOUT 10V/div 10ms/div
Figure 2a. MAX6397/MAX6398 GATE Waveform During Overvoltage Switch Mode
Figure 3. Overvoltage Switch Protection Configuration
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 overvoltage threshold is tripped, the internal fast comparator turns off the external MOSFET, pulling GATE to OUT within tOV and disconnecting the power source from the load. When IN decreases below the adjusted overvoltage threshold, the MAX6397/MAX6398 slowly enhance GATE above OUT, reconnecting the load to the power source.
VIN 10V/div
VGATE 10V/div
VOUT 10V/div
Overvoltage Limiter
4ms/div
Figure 2b. MAX6397/MAX6398 GATE Waveform During Overvoltage 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 (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.
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. 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, discharging the external GATE, regulating OUT at the set overvoltage threshold. OUT remains active during the overvoltage transients and the MOSFET continues to conduct during the overvoltage event, operating in switchedlinear mode.
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9
Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
COUT VPEAK GATE VBATT IN OUT R1
MAX6397 MAX6398 SET
VBATT GND R2
tRISE > 5ms
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. 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 capacitance. For a 6000pF Cgd, a 0.1F capacitor at GATE will reduce the impact of the fast-rising VIN input. Caution must be exercised when operating the MAX6397/MAX6398 in voltage-limiting mode for long durations. If the VIN is a DC voltage greater than the MOSFET's maximum gate voltage, the FET will dissipate power continuously. To prevent damage to the external MOSFET, proper heatsinking should be implemented.
characteristics of the charging system (Figure 5). These transients are capable of destroying semiconductors on the first `fault event.'
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. 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 (SET's input bias current) at the desired overvoltage threshold. For example: With an overvoltage threshold set to 20V: RTOTAL < 20V/(100 x ISET) where ISET is SET's 50nA input bias current. RTOTAL < 4M Use the following formula to calculate R2: R2 = VTH x R TOTAL VOV
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. Power in the alternator (essentially an inductor) 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
10
where VTH is the 1.215V SET rising threshold and VOV is the overvoltage threshold. R2 = 243k, use a 240k standard resistor. RTOTAL = R2 + R1, where R1 = 3.76M. Use a 3.79M standard resistor. A lower value for total resistance dissipates more power but provides slightly better accuracy.
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Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
GATE IN IN OUT R1 IN R1 IN
GATE OUT
MAX6397 MAX6398 SET
GND R2 R2
MAX6397
SET MAX6398 GND
Figure 6. Setting the MAX6397/MAX6398 Overvoltage Threshold
Q1
IN GATE VBATT LOAD VBATT
IN GATE LOAD
MAX6397 MAX6398
OUT GND
MAX6397 MAX6398
OUT GND
(a)
(b)
Figure 7. Reverse Battery Protection Using a Diode or p-Channel MOSFET
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 30m or less yields a forward-voltage drop of only a few millivolts (versus hundreds of millivolts for a diode, Figure 7a) thus improving efficiency. 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
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. 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 battery from the system. The zener diode and resistor combination prevent damage to the p-channel MOSFET during an overvoltage condition.
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11
Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
VBATT
1k
IN GATE VBATT CGATE COUT LOAD 60V TVS IN GATE LOAD
MAX6397 MAX6398
OUT GND
MAX6397 MAX6398
OUT GND
Figure 8. MAX6397/MAX6398 Controlling GATE Inrush Current
Figure 9. Protecting the MAX6397/MAX6398 Input from HighVoltage Transients
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 4.7F. 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 necessary to increase capacitance. Under normal conditions, use a 10F capacitor at IN. Larger input capacitor values and lower ESR provide better supply-noise rejection and line-transient response.
where IGATE is GATE's 75A sourcing current, ILOAD is the load current at startup, and C OUT is the output capacitor. Input Transients Clamping When the external MOSFET is turned off during an overvoltage 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: * Minimize stray inductance in the power path using wide traces, and minimize loop area including the power traces and the return ground path. * 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.
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 current can be approximated using the following formula: IINRUSH = COUT x IGATE + ILOAD CGATE
12
______________________________________________________________________________________
Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
VMAX VOV VBATT
+ VQ1 ILOAD
VBATT
GATE IN GATE 60V TVS OUT LOAD t1 OUT SET
t2
MAX6397 MAX6398
t3 tOVP
GND
Figure 11. MAX6397/MAX6398 Timing Diagram
Figure 10. Power Dissipated Across MOSFETs During an Overvoltage Fault (Overvoltage Limiter Mode)
MOSFET Selection Select external MOSFETs according to the application current level. The MOSFET's on-resistance (RDS(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: PQ1 = ILOAD2 x RDS(ON). The most power dissipation will occur during a prolonged 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: PQ1 = VQ1 x ILOAD where VQ1 is the voltage across the MOSFET's drain and source.
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. When the junction temperature exceeds TJ = +150C, 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 20C. Thermal-overload protection is designed to protect the MAX6397/ MAX6398 and the external MOSFET in the event of current-limit fault conditions. For continuous operation, do not exceed the absolute maximum junction-temperature rating of TJ = +150C.
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 different factors: * The device's ambient temperature (TA) * The output capacitor (COUT) * * * * The output load current (IOUT) The overvoltage threshold limit (VOV) The overvoltage waveform period (tOVP) The power dissipated across the package (PDISS)
Thermal Shutdown
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 temperature of the external nFET when the devices sit on the
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13
Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
180 JUNCTION TEMPERATURE (C) 170 160 150 CGATE = 10nF 140 130 120 1 CGATE = InF IOUT = 0 TA = +125C CGATE = 0 THERMAL SHUTDOWN
During t2, COUT loses charge through the output load. The voltage across COUT (V2) decreases until the MOSFET reaches its V GS(TH) threshold and can be approximated using the following formula: V2 = IOUT t2 COUT
CGATE = ADDITIONAL CAPACITANCE FROM GATE TO GND 10 100 1000
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 time for the OUT voltage to rise again to the overvoltage threshold can be approximated using the following formula: t 3 QGD VOUT x VGS _ QGD IGATE
OUTPUT CAPACITANCE (F)
Figure 12. Junction Temperature vs. COUT
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 current. The discharge time (t1) is approximately: t1 = COUT VOV x 0.05 IOUT + IGATEPD
where VOUT = ( VOV x 0.05) + V2. The total period of the overvoltage waveform can be summed up as follows: tOVP = t1 + t2 + t3 The MAX6397/MAX6398 dissipate the most power during an overvoltage event when IOUT = 0 (COUT is discharged only by the internal current sink). The maximum power dissipation can be approximated using the following equation: PDISS = VOV x 0.975 x IGATEPD x t1 t OVP
where VOV is the adjusted overvoltage threshold, IOUT is the external load current and IGATEPD is the GATE's internal 100mA (typ) pulldown current. 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 voltage 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: t2 = CISS VGS( TH) + VF IGATE
where CISS is the MOSFET's input capacitance, VGS(TH) is the MOSFET's gate-to-source threshold voltage, VF is the internal clamp diode forward voltage (VF = 1.5V typ), and IGATE is the MAX6397/MAX6398 charge-pump current (75A typ).
The die temperature (T J) increase is related to JC (8.3C/W and 8.5C/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: TJ = TA + PDISS x (JC + CA) < 170C (typical thermal-shutdown temperature) For the MAX6397, the power dissipation of the internal linear regulator must be added to the overvoltage protection circuit power dissipation to calculate the die temperature. The linear regulator power dissipation is calculated using the following equation: PREG = (VIN - VREG) (IREG) For example, using an IRFR3410 100V n-channel MOSFET, Figure 12 illustrates the junction temperature vs. output capacitor with I OUT = 0, T A = +125C, VOV < 16V,VF = 1.5V, IGATE = 75mA, and IGATEPD = 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
An additional capacitor can be added to GATE and GND to shift the curves as this increases t1. These values are used for illustration only. Customers must verify worst-case conditons for their specific application.
2.0 1.8 1.6 1.4 PD (W) 1.2 1.0 0.8 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 TEMPERATURE (C) DERATE 18.2mW/C ABOVE +70C
OUTPUT Current Calculation
The MAX6397 high input voltage (+72V max) provides up to 100mA of output current at REG. Package power dissipation 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 allowable package dissipation for a given ambient temperature. Alternately, use the following formula to calculate the allowable package dissipation: PDISS = 1.455W for TA +70C Maximum power dissipation = 1.455 - 0.0182 (TA - 70C) for +70C TA +125C where, 0.0182 W/C is the MAX6397 package thermal derating. After determining the allowable package dissipation, calculate the maximum output current using the following formula: IOUT(MAX) = PDISS VIN - VREG 100mA
MAX6397/MAX6398
1.455W
Figure 13. Maximum Power Dissipation vs. Temperature
Typical Application Circuit
DC-DC CONVERTER IN GND GATE 12V IN IN REG POK VCC RESET GPIO ALWAYS-ON C SHDN GND OUT OUT C
MAX6397
SET
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15
Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398
Typical Operating Circuit
DC-DC CONVERTER COUT COUT
DC-DC CONVERTER
GATE VBATT IN OUT R1 VBATT R1 IN
GATE OUT
MAX6397 REG MAX6398 SET
GND R2 R2
MAX6397
SET MAX6398 REG GND
OVERVOLTAGE LIMITER CONTROLLER
OVERVOLTAGE SWITCH CONTROLLER
Pin Configurations (continued)
TOP VIEW
OUT 6 *EP GATE 5 GND 4
Selector Guide
PART MAX6397LATA MAX6397MATA MAX6397SATA MAX6397TATA MAX6397YATA MAX6397ZATA MAX6397VATA MAX6397WATA REG OUTPUT POK ASSERTION VOLTAGE (V) THRESHOLD (%) 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 -- TOP MARK ANN ANO ANQ ANP ANK ANJ ANM ANL AJD
MAX6398
1 IN
2 SHDN
3 SET
MAX6398ATT
TDFN
*EXPOSED PAD. CONNECT TO GND.
Chip Information
TRANSISTOR COUNT: 590 PROCESS: BiCMOS
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Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
6, 8, &10L, DFN THIN.EPS
MAX6397/MAX6398
PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
21-0137
H
1
2
COMMON DIMENSIONS SYMBOL A D E A1 L k A2 MIN. 0.70 2.90 2.90 0.00 0.20 MAX. 0.80 3.10 3.10 0.05 0.40
PACKAGE VARIATIONS PKG. CODE T633-1 T633-2 T833-1 T833-2 T833-3 T1033-1 T1033-2 T1433-1 T1433-2 N 6 6 8 8 8 10 10 14 14 D2 1.500.10 1.500.10 1.500.10 1.500.10 1.500.10 1.500.10 1.500.10 1.700.10 1.700.10 E2 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 e 0.95 BSC 0.95 BSC 0.65 BSC 0.65 BSC 0.65 BSC 0.50 BSC 0.50 BSC 0.40 BSC 0.40 BSC JEDEC SPEC MO229 / WEEA MO229 / WEEA MO229 / WEEC MO229 / WEEC MO229 / WEEC MO229 / WEED-3 MO229 / WEED-3 ------b 0.400.05 0.400.05 0.300.05 0.300.05 0.300.05 0.250.05 0.250.05 0.200.05 0.200.05 [(N/2)-1] x e 1.90 REF 1.90 REF 1.95 REF 1.95 REF 1.95 REF 2.00 REF 2.00 REF 2.40 REF 2.40 REF
0.25 MIN. 0.20 REF.
PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
-DRAWING NOT TO SCALE-
21-0137
H
2
2
Revision History
Pages changed at Rev 3: 1, 14, 15, 17
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17 (c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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