19-3668; Rev 5; 1/09 KIT ATION EVALU E L B A AVAIL Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V 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 37µA 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 -40°C to +125°C. Applications Automotive Features 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 RDS(ON) 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) o Fully Specified from -40°C to +125°C (TJ) o Small, Thermally Enhanced 3mm x 3mm TDFN Package Ordering Information PART TEMP RANGE PIN-PACKAGE MAX6397_ATA-T* -40°C to +125°C 8 TDFN-EP** MAX6398ATT-T* -40°C to +125°C 6 TDFN-EP** *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. Selector Guide and Typical Operating Circuit appear at end of data sheet. Pin Configurations TOP VIEW REG OUT 8 7 GATE GND 6 5 *EP Industrial FireWire® MAX6397 Notebook Computers Wall Cube Power Devices FireWire is a registered trademark of Apple Computer, Inc. 1 2 3 4 IN SHDN SET POK TDFN *EXPOSED PAD. CONNECT TO GND. Pin Configurations continued at end of data sheet. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX6397/MAX6398 General Description MAX6397/MAX6398 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: IN, REG...............................................................................350mA All Remaining Pins ...................................................................50mA Continuous Power Dissipation (TA = +70°C) 6-Pin TDFN (derate 18.2mW/°C above +70°C) .............1455mW 8-Pin TDFN (derate 18.2mW/°C above +70°C) .............1455mW Operating Temperature Range (TA) ......................-40°C to +125°C Junction Temperature ...........................................................+150°C Storage Temperature Range .................................-65°C to +150°C Lead Temperature ................................................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = 14V; CGATE = 6000pF, CREG = 4.7µF, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = TJ = +25°C.) (Note 1) PARAMETER Supply Voltage Range SYMBOL CONDITIONS VIN Input Supply Current MIN SHDN = high, (MAX6398) 104 130 SHDN = low, no load (MAX6397) 37 45 IN Undervoltage Lockout Hysteresis VIN falling, disables GATE SET Input Current Startup Response Time GATE Output High Voltage GATE Output Low Voltage VOL IGATE GATE to OUT Clamp Voltage 5.50 1.181 1.215 -50 SHDN rising (Note 2) µA V mV 1.248 V % +50 nA 100 µs 1 ms SET rising from VTH - 100mV to VTH + 100mV 0.75 VOUT = VIN = 6V, RGATE to IN = 1MΩ VIN + 3.8V VIN + 4.2V VIN + 4.6V VOUT = VIN; VIN ≥ 14V, RGATE to IN = 1MΩ VIN + 8.5V VIN + 9.2V VIN + 11.5V VOH GATE Charge-Pump Current 20 5 175 GATE rising from GND to VOUT + 8V, CGATE = 6000pF, OUT = GND tOV 11 4 ISET GATE Rise Time SET to GATE Propagation Delay With respect to GND 4.66 VHYST tSTART V 140 VIN rising, enables GATE VTH UNITS 72 118 SHDN = low, (MAX6398) SET Threshold Hysteresis MAX SHDN = high, no load (MAX6397) IN Undervoltage Lockout SET Threshold Voltage TYP 5.5 µs V GATE sinking 20mA, VOUT = GND GATE = GND 0.38 V 18 µA V 75 VCLMP 13 SHDN Logic-High Input Voltage VIH 1.4 SHDN Logic-Low Input Voltage VIL 0.4 SHDN Input Pulldown Current VSHDN = 2V, SHDN is internally pulled down to GND Thermal Shutdown (Note 3) Thermal Shutdown Hysteresis 1 µA +150 °C 20 °C REGULATOR (MAX6397) Ground Current 2 IGND SHDN = GND IREG = 1mA 40 IREG = 100mA 60 _______________________________________________________________________________________ 48 µA Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V (VIN = 14V; CGATE = 6000pF, CREG = 4.7µF, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = TJ = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MAX6397L/M MAX6397S/T REG Output Voltage (VIN ≥ VREG + 1.8V) VREG MAX6397Y/Z MAX6397V/W Dropout Voltage (Note 4) ∆VDO Current Limit IREG = 1mA VOVP Overvoltage-Protection Sink Current IOVP Line Regulation (Note 5) ∆ VREG / ∆VREG ∆VREG / ∆IREG Load Regulation Power-Supply Rejection Ratio Startup Response Time POK Assertion Threshold (MAX6397 Only) tSTART VPOK_TH REG to POK Delay POK Output Low Voltage VOL MAX 5 5.120 3.3 3.360 1mA < IREG < 100mA 4.85 3.243 1mA < IREG < 100mA 3.201 IREG = 1mA 2.456 1mA < IREG < 100mA 2.41 IREG = 1mA 1.760 1mA < IREG < 100mA 1.715 3. 360 2.5 2.542 1.8 1.837 V 2.55 1.837 0.12 5.5V ≤ VIN ≤ 72V, IREG = 100mA, VREG = 5V 1.2 150 300 15 6.5V ≤ VIN ≤ 72V, IREG = 10mA, VREG = 5V mV/V mA % of VREG 105 VREG = 1.1 x VREG (nominal) UNITS 5.15 5.5V ≤ VIN ≤ 72V, IREG = 1mA, VREG = 5V mA 0.22 5.5V ≤ VIN ≤ 72V, IREG = 1mA, VREG = 5V 5.5V ≤ VIN ≤ 72V, IREG = 100mA, VREG = 5V 0.05 mV/V 0.8 mV/mA 1.5 1mA ≤ IREG ≤ 100mA, VREG = 5V IREG = 10mA, f = 100Hz, 0.5VP-P 55 dB RREG = 500Ω, VREG = 5V, CREG = 4.7µF 180 µs L 4.500 4.67 4.780 M 4.230 4.375 4.500 T 2.966 3.053 3.140 S 2.805 2.892 2.970 Z 2.250 2.304 2.375 Y 2.125 2.188 2.250 W 1.590 1.653 1.696 V 1.524 1.575 1.625 VREG rising or falling POK Leakage Current TYP IREG = 1mA VIN = 14V Overvoltage-Protection Threshold MIN 4.925 35 V µs VPOK = 5V 300 nA VIN ≥ 1.5V, ISINK = 1.6mA, POK asserted 0.3 V Note 1: Specifications to TA = -40°C 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. _______________________________________________________________________________________ 3 MAX6397/MAX6398 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VIN = 14V, CREG = 4.7µF, IREG = 0, unless otherwise noted.) SUPPLY CURRENT vs. INPUT VOLTAGE 100 80 160 150 VIN = 72V 140 130 120 VIN = 14V 110 20 30 40 50 60 70 -25 0 25 50 75 100 125 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 120 VIN = 72V 110 100 VIN = 14V REGULATOR ON GATE OFF 45 40 35 30 90 25 80 20 20 MAX6397-98 toc06 50 MAX6398 GATE OFF 18 16 SUPPLY CURRENT (µA) MAX6398 GATE ON MAX6397-98 toc05 MAX6397-98 toc04 SUPPLY CURRENT (µA) 70 INPUT VOLTAGE (V) 140 130 80 40 -50 80 SUPPLY CURRENT (µA) 10 90 50 80 0 100 60 90 40 MAX6398 GATE ON 110 100 60 MAX6397-98 toc03 120 MAX6397-98 toc02 MAX6397 170 SUPPLY CURRENT (µA) 120 180 SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) MAX6397-98 toc01 MAX6397 GATE ON 140 SUPPLY CURRENT vs. INPUT VOLTAGE SUPPLY CURRENT vs. TEMPERATURE 160 14 12 10 8 6 4 2 0 25 50 75 100 10 20 50 40 30 60 TEMPERATURE (°C) INPUT VOLTAGE (V) GATE-DRIVE VOLTAGE vs. INPUT VOLTAGE UVLO THRESHOLD vs. TEMPERATURE 80 5.6 VUVLO (V) 4 5.2 5.0 4.8 4.6 2 4 6 8 10 12 14 16 18 20 22 24 INPUT VOLTAGE (V) 60 80 1.240 1.236 1.232 1.228 1.224 1.220 1.216 1.212 4.4 1.208 4.2 1.204 4.0 0 40 SET THRESHOLD vs. TEMPERATURE 5.4 6 20 INPUT VOLTAGE (V) 5.8 8 0 SET THRESHOLD (V) VOUT = VIN 10 70 6.0 MAX6397-98 toc07 12 4 0 0 125 MAX6397-98 toc09 -25 MAX6397-98 toc08 -50 VGATE - VOUT (V) MAX6397/MAX6398 Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V 1.200 -50 -25 0 25 50 75 TEMPERATURE (°C) 100 125 -50 -25 0 25 50 75 TEMPERATURE (°C) _______________________________________________________________________________________ 100 125 Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V 1.6 DROPOUT VOLTAGE (V) 16.8 16.7 16.6 16.5 16.4 16.3 MAX6397L 1.8 1.4 MAX6397L 5.15 TA = +125°C 1.2 1.0 0.8 TA = +25°C 0.6 16.2 0.4 16.1 0.2 16.0 5.20 REG OUTPUT VOLTAGE (V) 16.9 MAX6397-98 toc11 2.0 MAX6397-98 toc10 0 -50 -25 0 25 50 75 100 125 5.10 ILOAD = 10mA ILOAD = 50mA 5.05 5.00 ILOAD = 100mA 4.95 TA = -40°C 4.90 0 20 40 60 -40 -25 -10 5 20 35 50 65 80 95 110 125 80 100 120 140 160 180 REG LOAD CURRENT (mA) TEMPERATURE (°C) MAXIMUM REG OUTPUT VOLTAGE vs. LOAD CURRENT AND TEMPERATURE GATE-DRIVE VOLTAGE vs. TEMPERATURE POWER-SUPPLY REJECTION RATIO vs. FREQUENCY 4.8 TA = +25°C 4.6 TA = +125°C 4.4 THERMAL SHUTDOWN 10.495 0 10.490 CREG = 10µF IREG = 10mA -10 -20 10.485 10.480 10.475 10.470 10.465 -30 -40 -50 10.460 4.2 -60 10.455 -70 10.450 4.0 0 MAX6397-98 toc15 5.0 10.500 PSRR (dB) TA = -40°C GATE-DRIVE VOLTAGE (V) 5.2 MAX6397-98 toc13 TEMPERATURE (°C) MAX6397-98 toc14 GATE-TO-OUT CLAMP VOLTAGE (V) 17.0 REG OUTPUT VOLTAGE (V) REG OUTPUT VOLTAGE vs. LOAD CURRENT AND TEMPERATURE DROPOUT VOLTAGE vs. REG LOAD CURRENT MAX6397-98 toc12 GATE-TO-OUT CLAMP VOLTAGE vs. TEMPERATURE 40 80 120 160 200 240 280 320 360 400 -50 -25 0 25 50 75 100 125 10 STARTUP WAVEFORM (RLOAD = 100Ω, CIN = 10µF, COUT = 10µF) MAX6397-98 toc16 100 1k 10k 100k 1M 10M FREQUENCY (Hz) TEMPERATURE (°C) LOAD CURRENT (mA) STARTUP WAVEFORM FROM SHUTDOWN (CIN = 10µF, COUT = 10µF) MAX6397-98 toc17 RLOAD = 100Ω VIN 10V/div VSHDN 2V/div VGATE 10V/div VGATE 10V/div VOUT 10V/div VOUT 10V/div IOUT 200mA/div IOUT 200mA/div 4ms/div 400µs/div _______________________________________________________________________________________ 5 MAX6397/MAX6398 Typical Operating Characteristics (continued) (VIN = 14V, CREG = 4.7µF, IREG = 0, unless otherwise noted.) MAX6397/MAX6398 Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V Typical Operating Characteristics (continued) (VIN = 14V, CREG = 4.7µF, IREG = 0, unless otherwise noted.) VOLTAGE LIMIT FAULT OVERVOLTAGE SWITCH FAULT MAX6397-98 toc19 MAX6397-98 toc18 VOV = 30V VOV = 30V VIN 20V/div VIN 20V/div VGATE 20V/div VGATE 20V/div VOUT 20V/div VOUT 20V/div VREG 5V/div VREG 5V/div 1ms/div 200µs/div TRANSIENT RESPONSE REG LOAD-TRANSIENT RESPONSE MAX6397-98 toc20 MAX6397-98 toc21 CREG = 10µF IREG = 10mA CREG = 10µF VREG AC-COUPLED 500mV/div VIN 10V/div IREG 100mA/div VREG 100mV/div 400µs/div 1ms/div REGULATOR POK ASSERTION REGULATOR STARTUP WAVEFORM MAX6397-98 toc23 MAX6397-98 toc22 IREG = 10mA VREG 2V/div VIN 10V/div 0V VREG 2V/div VPOK 2V/div VPOK 2V/div 0V IREG = 0 0A 1ms/div 6 IREG 200mA/div 100µs/div _______________________________________________________________________________________ Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V PIN NAME FUNCTION MAX6397 MAX6398 1 1 IN 2 2 SHDN 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. 3 3 SET 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. 4 — POK 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. 5 4 GND Ground Supply Voltage Input. Bypass with a minimum 10µF capacitor to GND. 6 5 GATE 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. 7 6 OUT Output-Voltage-Sense Input. Connect to the source of the external n-channel MOSFET. 8 — REG 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. — — EP Exposed Pad. Connect to ground plane. 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 100µs delay before GATE enhancement commences. _______________________________________________________________________________________ 7 MAX6397/MAX6398 Pin Description Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398 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 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. IN THERMAL PROTECTION UVLO 10V CHARGE PUMP 5V Power-OK Output GATE SET OUT 1.23V SHDN LINEAR REGULATOR MAX6397 MAX6398 REG POK VPOK_TH GND MAX6397 ONLY 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 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 logic-output level down to VIN = 1.5V. 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 75µA 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. _______________________________________________________________________________________ Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V GATE VBATT IN OUT R1 VGATE 10V/div VOUT 10V/div MAX6397 SET MAX6398 R2 GND 10ms/div Figure 2a. MAX6397/MAX6398 GATE Waveform During Overvoltage Switch Mode VIN 10V/div VGATE 10V/div VOUT 10V/div 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. 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. _______________________________________________________________________________________ 9 MAX6397/MAX6398 VIN 10V/div MAX6397/MAX6398 Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V COUT VPEAK GATE VBATT IN OUT R1 MAX6397 MAX6398 SET tRISE > 5ms VBATT GND R2 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 semiconductors on the first ‘fault event.’ 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 0.1µF 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. 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. 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 Setting Overvoltage Thresholds 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 < 4MΩ Use the following formula to calculate R2: R2 = VTH × R TOTAL VOV where VTH is the 1.215V SET rising threshold and VOV is the overvoltage threshold. R2 = 243kΩ, use a 240kΩ standard resistor. RTOTAL = R2 + R1, where R1 = 3.76MΩ. Use a 3.79MΩ standard resistor. A lower value for total resistance dissipates more power but provides slightly better accuracy. ______________________________________________________________________________________ Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V IN MAX6397/MAX6398 GATE IN GATE IN OUT R1 IN R1 MAX6397 MAX6398 SET MAX6397 SET MAX6398 R2 GND OUT R2 GND Figure 6. Setting the MAX6397/MAX6398 Overvoltage Threshold Q1 IN IN GATE GATE VBATT LOAD VBATT LOAD MAX6397 MAX6398 MAX6397 MAX6398 OUT OUT GND 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 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. 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. ______________________________________________________________________________________ 11 MAX6397/MAX6398 Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V VBATT 1kΩ IN GATE CGATE VBATT COUT IN LOAD MAX6397 MAX6398 GATE 60V TVS OUT LOAD MAX6397 MAX6398 GND OUT GND Figure 8. MAX6397/MAX6398 Controlling GATE Inrush Current 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 necessary to increase capacitance. Under normal conditions, use a 10µF capacitor at IN. Larger input capacitor values and lower ESR provide better supply-noise rejection and line-transient response. 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 = 12 Figure 9. Protecting the MAX6397/MAX6398 Input from HighVoltage Transients where IGATE is GATE’s 75µA 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. COUT × IGATE + ILOAD CGATE ______________________________________________________________________________________ Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V VOV + VQ1 - VBATT VBATT ILOAD GATE t2 IN GATE OUT 60V TVS LOAD t1 MAX6397 MAX6398 t3 OUT SET 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. 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 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 = +150°C, 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 current-limit fault conditions. For continuous operation, do not exceed the absolute maximum junction-temperature rating of TJ = +150°C. 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) ______________________________________________________________________________________ 13 MAX6397/MAX6398 VMAX 180 JUNCTION TEMPERATURE (°C) MAX6397/MAX6398 Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V IOUT = 0 TA = +125°C 170 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: THERMAL SHUTDOWN CGATE = 0 160 ∆V2 = IOUT 150 CGATE = 10nF 140 CGATE = InF 130 CGATE = ADDITIONAL CAPACITANCE FROM GATE TO GND 120 1 10 100 1000 OUTPUT CAPACITANCE (µF) 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 × 0.05 IOUT + IGATEPD 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 (75µA typ). ∆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 time for the OUT voltage to rise again to the overvoltage threshold can be approximated using the following formula: ∆t 3 ≅ QGD ∆VOUT × VGS _ QGD IGATE 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 × 0.975 × IGATEPD × ∆t1 ∆t OVP The die temperature (T J) increase is related to θJC (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: TJ = TA + PDISS x (θJC + θCA) < 170°C (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 = +125°C, 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 2.0 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 ≤ +70°C Maximum power dissipation = 1.455 - 0.0182 (TA - 70°C) for +70°C ≤ TA ≤ +125°C where, 0.0182 W/°C is the MAX6397 package thermal derating. 1.455W 1.8 1.6 DERATE 18.2mW/°C ABOVE +70°C PD (W) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 20 40 60 80 After determining the allowable package dissipation, calculate the maximum output current using the following formula: 100 120 140 160 TEMPERATURE (°C) Figure 13. Maximum Power Dissipation vs. Temperature IOUT(MAX) = PDISS VIN − VREG ≤ 100mA Typical Application Circuit DC-DC CONVERTER IN OUT µC GND GATE 12V IN OUT IN REG MAX6397 SET POK VCC RESET SHDN GND GPIO ALWAYS-ON µC ______________________________________________________________________________________ 15 MAX6397/MAX6398 OUTPUT Current Calculation 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. Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V MAX6397/MAX6398 Typical Operating Circuit DC-DC CONVERTER DC-DC CONVERTER COUT COUT GATE VBATT IN GATE VBATT OUT R1 IN OUT R1 MAX6397 REG MAX6398 SET MAX6397 SET MAX6398 REG R2 GND OVERVOLTAGE LIMITER CONTROLLER R2 GND OVERVOLTAGE SWITCH CONTROLLER Selector Guide Pin Configurations (continued) TOP VIEW PART OUT GATE GND 6 5 4 *EP MAX6398 1 2 3 IN SHDN SET REG OUTPUT POK ASSERTION VOLTAGE (V) THRESHOLD (%) MAX6397LATA 5.0 92.5 ANN MAX6397MATA 5.0 87.5 ANO MAX6397SATA 3.3 87.5 ANQ MAX6397TATA 3.3 92.5 ANP MAX6397YATA 2.5 87.5 ANK MAX6397ZATA 2.5 92.5 ANJ MAX6397VATA 1.8 87.5 ANM MAX6397WATA 1.8 92.5 ANL MAX6398ATT — — AJD TDFN *EXPOSED PAD. CONNECT TO GND. 16 TOP MARK ______________________________________________________________________________________ Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V TRANSISTOR COUNT: 590 PROCESS: BiCMOS For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 6 TDFN T633-2 21-0137 8 TDFN T833-2 21-0137 ______________________________________________________________________________________ 17 MAX6397/MAX6398 Package Information Chip Information MAX6397/MAX6398 Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V Revision History REVISION NUMBER REVISION DATE PAGES CHANGED 0 5/05 Initial release 3 1/07 Changed formula and updated Figure 13 caption title. 4 3/07 Updated Electrical Characteristics table. 1, 3, 18 5 1/09 Updated Electrical Characteristics table. 3 DESCRIPTION — 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. 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.