FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Features Description The AccuPower™ FPF270X series is a family of current-limit load switches that provide full protection to systems and loads from excess current conditions. Minimum current limit is adjustable from 0.4A to 2.0A. The FPF270X contains a slew-rate-controlled N-channel MOSFET and slew-rated turn-on to prevent power bus disturbances from being caused by “hot plugging” loads or momentary excess load demands. The input voltage range is 2.8V to 36V. Loads can be activated or deactivated with a low-voltage logic-compatible ON pin. Fault conditions can be monitored using the error flag pin and/or the power-good pin. 2.8V to 36V Input Voltage Range Typical RDS(ON)=88m 0.4A to 2A Adjustable Current Limit (Min.) Slew Rate Controlled ESD Protected, above 2000V HBM Thermal Shutdown Active LOW Enable UVLO Protection Power-Good Output Applications Each member of the FPF270X family serves a category of load-fault response. All devices clamp the load current so that it cannot exceed an externally programmed current level. An over temperature feature provides further device protection in case of excessive levels of power dissipation. Motor Drives Digital Cameras Consumer Electronics Industrial FPF2700 responds to an overload condition that lasts longer than a fixed blanking period by turning off the load, followed by a retry after the auto-restart time. Computing Hard Disk Drives Telecom Equipment FPF2701 responds to an overload condition that lasts longer than a fixed blanking period by latching off the load. The load remains off unless either the ON pin is toggled or the input voltage cycles through UVLO. Figure 1. MLP (Top View) Figure 2. MLP (Bottom View) FPF2702 is intended to be used with external fault management. Like the FPF2700 and FPF2701, it sets the fault signal pin LOW when it activates current clamping. This device is intended for applications where external fault management coordinates the overload response with the FPF2702. The FPF270X is available in a space-saving Pb and Halogen free, 8-lead MLP 3x3mm and SO8 packages. Figure 3. SO8 (Top View) Ordering Information Part Number Current Limit [A] Current Limit Blanking Time [ms] Auto-Restart Time [ms] ON Pin Activity Package FPF2700MPX 0.4 – 2.0 0.5 127.5 Active LOW MLP3X3 FPF2701MPX 0.4 – 2.0 0.5 NA Active LOW MLP3X3 FPF2702MPX 0.4 – 2.0 NA NA Active LOW MLP3X3 FPF2700MX 0.4 – 2.0 0.5 127.5 Active LOW SO8 FPF2701MX 0.4 – 2.0 0.5 NA Active LOW SO8 FPF2702MX 0.4 – 2.0 NA NA Active LOW SO8 © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 www.fairchildsemi.com FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches January 2011 36V MAX. VIN VOUT ON FLAGB TO LOAD OFF ON VIN 2.8V – 36V CIN ISET PGOOD RSET GND Figure 4. Typical Application Block Diagram COUT FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Application Diagram Figure 5. Block Diagram © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 www.fairchildsemi.com 2 VOUT 8 1 VIN FLAGB 7 2 PGOOD VIN 1 8 VOUT PGOOD 2 7 FLAGB ISET 3 6 NC ON 4 5 GND GND NC 6 3 ISET GND 5 4 ON Figure 6. MLP (Bottom View) Figure 7. SO8 (Top View) Pin Definitions Pin # Name Description 1 VIN 2 PGOOD Power-Good Output. Open-drain output to indicate that output voltage has reached 90% of input voltage. 3 ISET Current Limit Set Input. A resistor from ISET to ground sets the current limit for the switch. 4 ON 5 GND 6 NC Supply Input. Input to the power switch and the supply voltage for the IC. ON Control Input. Active LOW. Ground No connection. Leave open or connect to ground. 7 FLAGB Fault Output. Active LOW, open-drain output that indicates current limit, under-voltage, or over -temperature state. 8 VOUT Switch Output. Output of the power switch. © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Pin Configurations www.fairchildsemi.com 3 Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only. Symbol Parameter Min. Max. Unit PGOOD, FLAGB, VIN to GND -0.3 40 V VOUT to GND -0.3 VIN + 0.3 V 6 V ON to GND PD -0.3 Power Dissipation (TA=25°C) MLP 3x3(1), See Figure 8 1.25 SO8(1), See Figure 10 1.00 W ISW Maximum Continuous Switch Current 3.5 A TJ Operating Junction Temperature -40 +125 °C TSTG Storage Temperature -65 +150 °C ESD Electrostatic Discharge Protection Level JA Thermal Resistance, Junction to Ambient Human Body Model, JESD22-A114 2000 Charged Device Model, JESD22-C101 2000 (1) MLP 3x3 , See Figure 8 V 80 (1) SO8 , See Figure 10 102 °C/W Note: 1. Thermal resistance, θJA, is determined with the device mounted on a one inch square pad, 2oz copper pad, and a 1.5 x 1.5in. board of FR-4 material. 2 Figure 8. 80°C/W Mounted on a 1in Pad of 2oz. Copper Figure 9. 226°C/W Mounted on a Minimum Pad of 2oz. Copper 2 Figure 10. 102°C/W mounted on a 1in Pad of 2oz. Copper Figure 11. 181°C/W Mounted on a Minimum Pad of 2oz. Copper Recommended Operating Conditions The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding them or designing to Absolute Maximum Ratings. Symbol Parameter Min. Max. Unit VIN Input Supply Voltage 2.8 36.0 V TA Ambient Operating Temperature -40 85 °C © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Absolute Maximum Ratings www.fairchildsemi.com 4 VIN=2.8 to 36V and TA=-40 to +85°C unless otherwise noted. Typical values are at VIN=12V and TA=25°C. Symbol Parameter Conditions Min. Typ. Max. Unit Basic Operation VIN Operating Voltage IQ Quiescent Current VIN=12V, VON=0V, IOUT=0A ISHDN Shutdown Current VIN=36V, VON=3.3V, IOUT=0A TA=25°C, VIN=12V RON On-Resistance 2.8 36.0 V 140 μA 5 14 μA 88 114 92 TA=-40 to +85°C, VIN=12V 140 TA=25°C, VIN=5V 88 TA=-40 to +85°C, VIN=5V VIH ON Input Logic HIGH Voltage VIN=2.8 to 36V VIL ON Input Logic LOW Voltage VIN=2.8 to 36V 114 mΩ 140 2.0 V V 1 μA ILK ON Input Leakage VON=5.5V or GND ISWOFF Off Switch Leakage VIN=36V, VON=3.3V, VOUT=0V 0.01 FLAGB Output Logic LOW Voltage VIN=5V, ISINK=1mA 0.1 IFLAGB(HI) FLAGB Output Logic HIGH Leakage Current VIN=36V, Switch On, VFLAGB=36V VPGOOD PGOOD Trip Voltage VIN=5V, VOUT as Percent of VIN, VOUT Rising 90 % VPGOOD(HYS) PGOOD Hysteresis VIN=5V, VOUT as Percent of VIN, VOUT Falling 3 % VPGOOD(LO) PGOOD Output Logic LOW Voltage VIN=5V, ISINK=1mA VFLAGB(LO) IPGOOD(HI) -1 0.8 0.1 VIN=36V, Switch ON, PGOOD Output High Leakage Current VPGOOD=36V μA 0.2 V 1 μA 0.2 V 1 μA 1.2 x INOM A Protections ILIM Current Limit TA=25°C ISC Short Circuit Current Limit VOUT < 2V, Switch in OverCurrent Condition TSD UVLO Thermal Shutdown Under-Voltage Shutdown 0.8 x INOM 1.0 x INOM 0.75 x INOM Shutdown Threshold 140 Return from Shutdown 110 Hysteresis 30 VIN Increasing 2.3 UVLO_HYST Under-Voltage Shutdown Hysteresis 2.5 A °C 2.7 100 V mV Dynamic tdon Turn On Delay tdoff Turn Off Delay tR VOUT Rise Time tF VOUT Fall Time tBLANK tRESTART tCLR Over-Current Blanking Time 2.7 0.1 RL=500Ω, CL=2uF ms 7.5 1.5 FPF2700/1, TA=25°C 0.25 0.50 0.75 ms Auto-Restart Time FPF2700, TA=25°C 63.8 127.5 191.2 ms Current-Limit Response Time VIN=12V, VON=0V © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 50 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Electrical Characteristics μs www.fairchildsemi.com 5 90 90 10 10 VOUT tR 3.3 VON tF 50 50 90 10 VOUT tdon tdoff tON = tR + tdon tOFF = tF + tdoff Figure 12. Timing Diagram Typical Performance Characteristics VIN = 12V and TA = 25°C. 1.80 1.40 TA = 25°C V IN = 12V 1.70 1.38 1.35 On Threshold Voltage (V) On Threshold Voltage (V) 1.60 V IH 1.33 1.30 V IL 1.28 1.50 1.40 VIH 1.30 V IL 1.20 1.10 1.25 1.00 1.23 0.90 1.20 0.80 0 5 10 15 20 25 30 35 ‐50 40 ‐25 0 25 Figure 13. ON Threshold vs. Supply 75 100 125 150 Figure 14. ON Threshold vs. Temperature 12 130 VON = 0V TA = 125°C VON = 5V 120 TA = 125°C 10 TA = 85°C TA = 85°C 110 Quiescent Current (µA) Quiescent Current (µA) 50 TJ, Junction Temperature (oC) Supply Voltage (V) TA = 25°C 100 90 TA = ‐40°C 80 8 TA = 25°C 6 TA = ‐40°C 4 2 70 60 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Timing Diagram 0 0 5 10 15 20 25 30 35 0 40 Supply Voltage (V) 5 10 15 20 25 30 35 40 Supply Voltage (V) Figure 15. Quiescent Current vs. Supply Voltage (ON) Figure 16. Quiescent Current vs. Supply Voltage (OFF) © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 www.fairchildsemi.com 6 VIN = 12V and TA = 25°C. Figure 17. On Resistance vs. Supply Voltage Figure 18. On Resistance vs. Junction Temperature 4.0 VIN = 12V RL = 500 CL = 2µF Turn‐On Delay (ms) 3.5 3.0 2.5 2.0 1.5 1.0 ‐50 ‐25 0 25 50 75 100 125 150 TJ, Junction Temperature (oC) Figure 19. Turn-On Delay vs. Junction Temperature Figure 20. Output Rise Time vs. Junction Temperature Figure 21. Turn-Off Delay vs. Junction Temperature Figure 22. Output Fall Time vs. Junction Temperature © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Typical Performance Characteristics www.fairchildsemi.com 7 When VOUT<2V, the current limit is set to 75% of ILIM. Figure 23. Normal Startup to 0.5X ILIM Figure 24. OUT Shorted to GND, Short Condition Persists (SOA Protection Followed by Current-Limited Operation) Figure 25. OUT Overloaded with 1.5X ILIM (Long-Duration Overload) Figure 26. OUT Shorted to GND, Short Condition Removed (SOA Protection Followed by Normal Operation) Figure 27. OUT Overloaded with 1.5X ILIM (Transient Overload) © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Typical Operation Characteristics of FPF2700 and FPF2701 www.fairchildsemi.com 8 Figure 28. OUT Shorted to GND, Short Condition Persists (SOA Protection Current Limit Followed by Current Limit) Figure 29. OUT Overloaded with 1.5X ILIM (Long-Duration Overload) © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Typical Operation Characteristics of FPF2702 www.fairchildsemi.com 9 VIN = 12V and TA = 25°C. Figure 30. 12V Turn-On Delay (RL=500, COUT=2µF) Figure 31. 12V Turn-Off Delay (RL=500, COUT=2µF) Figure 32. 12V Blanking Time (Output Overloaded and tblank Expired, FPF2700/01, ILIM=1A, ILOAD=3.3A, COUT=µF, RLOAD=500) VOC(2) Figure 33. 12V Restart Time (Switch Turned ON into Persistent Over-Current Condition,tRESTART~127.5ms) FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Typical Performance Characteristics FPF270X Figure 34. Soft Overload and Constant Current Figure 35. OUT Shorted to GND, Short Condition (ILOAD > ILIM, FPF2702 Enters Constant Current Mode, Removed (SOA Protection Followed by a Normal Running at ILIM) Operation, FPF2700 / FPF2701) Note: 2. VOC signal forces the device into an over-current condition by loading a 500m resistor to the output through an NMOS. VOC is the gate drive of the NMOS. © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 www.fairchildsemi.com 10 Description of Operation Current Limiting The FPF270X family of current limit load switches is designed to meet the power requirements of a variety of applications with wide input voltage range of 2.8V to 36V and adjustable current-limit value. The FPF270X family offers control and protection while providing optimum operation current for safe design practices. The core of each switch is a typical 88mΩ (VIN = 12V) N-channel MOSFET and a controller capable of functioning over an input voltage range of 2.8V to 36V. The current limit ensures that the current through the switch doesn't exceed a maximum value while not limiting at less than a minimum value. The current-limit level is adjustable through an external resistor connected between the ISET pin and GND. The typical current limit level is adjustable from 500mA to 2.5A. The minimum current limit (ILIM(MIN)) range is from 0.4A to 2.0A, including 20% current-limit tolerance. The FPF2700 and FPF2701 have a blanking time during which the switch acts as a constant-current source (Figure 27). If the over-current condition persists beyond the blanking time, the FPF2700 latches off and shuts the switch off (Figure 32). If the ON pin is kept active, an auto-restart feature releases the switch and turns the switch on again after the auto-restart time (Figure 33). If the over-current condition persists beyond the blanking time, the FPF2701 latch-off feature shuts the switch off. The switch is kept off until the ON pin is toggled or input power is cycled. The FPF2702 has no current-limit blanking period, so it remains in a constant-current state until the ON pin is deactivated or the thermal shutdown turns off the switch. FPF270X offers adjustable current limiting, undervoltage lockout (UVLO), power-good indicator (PGOOD), fault flag output (FLAGB), and thermal shutdown protection. In the event of an over-current condition, the load switch limits the load to the current limit value. The current limit value for each switch can be adjusted from 400mA to 2A through the ISET pin. On/Off Control The ON pin is active LOW for and controls the state of the switch. Pulling the ON pin continuously to LOW holds the switch in ON state. The switch moves into OFF state when the ON pin is pulled HIGH. The ON pin can be pulled HIGH to a maximum voltage of 5.5V. Besides the current-limiting functionality, the switch is protected by the thermal shutdown protection and an independent SOA protection circuit is available. An under-voltage condition on the input voltage or a junction temperature in excess of 140°C overrides the ON control and turns off the switch. In addition, an overcurrent condition causes the switch to turn off in the FPF2700 and FPF2701 after the expiration of the blanking time. The FPF2700 has an auto-restart feature that automatically turns the switch ON again after the auto-restart time. For the FPF2701, the ON pin must be toggled to turn the switch on again. The FPF2702 does not turn off in response to an over-current condition; it remains operating in Constant-Current Mode as long as ON is enabled and the thermal shutdown or UVLO have not activated. The ON pin does not have internal pulldown or pull-up resistors and should not be left floating. FPF270X has an SOA protection feature to protect the load switch in response to current surges exceeding 12A in normal operation. If a short-circuit event occurs (IOUT>12A), the switch is turned off in about 1µs by an independent Safe Operating Area (SOA) protection circuit (Figure 26, Figure 28). This feature protects the switch in case of sudden, high-current events at the output, such as a short to GND. The switch turns on automatically after a turn-on delay of about 2.7ms. Fault Reporting Short-Circuit Current Limit (VOUT < VSCTH = 2V) Upon detection of an over-current condition, an input UVLO, or an over-temperature condition, the FLAGB signals the Fault Mode by activating LOW. In the event of an over-current condition for the FPF2700 or FPF2701, the FLAGB goes LOW at the end of the blanking time (Figure 24 and Figure 25). FLAGB goes LOW immediately for the FPF2702 (Figure 29). If the over-current condition lasts longer than blanking time, FLAGB remains LOW through the auto-restart time for the FPF2700. For the FPF2701, FLAGB is latched LOW and ON must be toggled to release it. When the output voltage drops below the short-circuit threshold voltage, VSCTH, the current-limit value reconditions itself to the short-circuit current limit value, which is 75% of the nominal current limit (0.75 x ILIM,) (Figure 24). This prevents early thermal shutdown by reducing the power dissipation of the device. The VSCTH value is set at 2V. At about VOUT = 2.1V, the switch is removed from short-circuit current-limiting mode and the current limit is set to the nominal current limit value. For FPF2702, FLAGB is LOW during a fault and immediately returns HIGH at the end of the fault condition. FLAGB is an open-drain MOSFET that requires a pull-up resistor. The maximum pull-up voltage is 36V (Figure 29). The FPF270X has an adjustable 0.4A to 2.0A minimum current limit set through an external resistor, RSET, connected between ISET and GND. A precision RSET value must be used, such as 1% tolerance or lower, to minimize the total current limit tolerance of the system. During shutdown, the pull-down on FLAGB is disabled to reduce current draw from the supply. A 100KΩ pull-up resistor is recommended in the application. Use the following equation to calculate the value of the resistor for intended typical current limit value: © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 SOA Protection Current Limit (IOUT > 12A) Setting the Current Limit Value FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Application Information www.fairchildsemi.com 11 277 .5 ILIM( TYP ) ( A ) Power Good (1) FPF270X has a power good feature. The PGOOD pin is an open-drain MOSFET that asserts HIGH when the output voltage reaches 90% of the input voltage (Figure 26). A typical 3% PGOOD hysteresis is added to PGOOD to prevent PGOOD from chattering as VOUT falls near the PGOOD threshold voltage. ILIM(TYP) is the typical current limit value based on a given RSET. Table 1. RSET Selection Guide Current Limit [A] RSET (k) Min. Typ. Max. 111 2.00 2.50 3.00 20 124 1.79 2.24 2.69 20 147 1.51 1.89 2.27 20 182 1.22 1.52 1.83 20 220 1.01 1.26 1.51 20 274 0.81 1.01 1.22 20 374 0.59 0.74 0.89 20 549 0.40 0.51 0.61 20 Tol. (%) The PGOOD pin requires an external pull-up resistor connected to an external voltage source compatible with input levels of other chips connected to this pin. PGOOD is kept LOW when the device is inactive. To save current in the OFF state, the pull-up resistor of the PGOOD pin can be connected to the output voltage when there is no battery, provided that compatibility with the input levels of other devices connected to PGOOD is observed. A typical value of 100kΩ is recommended for the pull up resistor. When the power-good feature is not used in the application, the PGOOD pin can be connected to GND. Thermal Shutdown 2.8 Thermal shutdown protects the die from internally or externally generated excessive temperatures. During an over-temperature condition; as the temperature increases above 140°C, FLAGB is activated and the switch is turned off. 2.6 2.4 2.2 2.0 ILIMIT (A) 1.8 1.6 When the die cools down sufficiently (die temperature drops below the threshold level), the switch automatically turns on again. To avoid unwanted thermal oscillations, a 30°C (typical) thermal hysteresis is implemented between thermal shutdown entry and exit temperatures. Proper board layout is required to prevent premature thermal shutdown (see Figure 38 for thermal shutdown behavior on FPF2702). 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 100 200 300 400 500 600 RSET (k) Figure 36. ILIM vs. RSET Under-Voltage Lockout (UVLO) The under-voltage lockout feature turns off the switch if the input voltage drops below the under-voltage lockout threshold. With the ON pin active (ON pin pulled LOW), the input voltage rising above the under-voltage lockout threshold causes a controlled turn-on of the switch (Figure 37). The UVLO threshold voltage is set internally at 2.5V for VIN rising. The under-voltage lockout threshold has a 0.1V hysteresis. Figure 38. FPF2702 Thermal Shutdown Behavior FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches R SET (K ) Figure 37. Under-Voltage Lockout Performance © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 www.fairchildsemi.com 12 It is possible to estimate the SOA for the two FPF2702 packages, MPX and MX, through their respective SOA curves shown in Figure 39 and Figure 40. These curves provide a reference on how long the load switch survives under the worst-case scenario with minimum pad size of one square inch.(1) During extended output-short conditions, excessive power dissipation occurs in the load switch. FPF2700 and PFP2701 are protected by turning off the load switch after blanking time. FPF2702 has no blanking time feature; please refer to Note 3. Figure 39. FPF2702 MPX SOA Figure 40. FPF2702 MX SOA Note: 3. To protect FPF2702 from an extended short condition, additional protection must be implemented in the system to protect the device. For example, the FLAGB and PGOOD signal can be used to monitor the short-circuit fault condition. In applications where FPF2702 can be exposed to persistent short-circuit conditions, it should be used only with external fault management control to protect the switch. © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches SOA (FPF2702) www.fairchildsemi.com 13 Power Dissipation To limit the voltage drop on the input supply caused by transient inrush currents when the switch is turned on into a discharged load capacitor or short-circuit; an input capacitor, CIN, is recommended between the IN and GND pins. The FPF270X features a fast current limit response time (50μs). During this period, the device relies on the input capacitor to supply the load current. A 10μF to 100μF ceramic capacitor is adequate for CIN in most cases. Larger CIN values may be required in highvoltage or high-current applications. An electrolytic capacitor can be used in parallel to further reduce the voltage drop. During normal operation as a switch, the power dissipation of the device is small and has little effect on the operating temperature of the part. The maximum power dissipation for the switch in normal operation occurs just before the switch enters into current limit. This may be calculated using the equation: PD _ MAX ( NormalOper (3) ) 125°C under normal operation. Junction temperature can be calculated using the equation: TJ PD JA TA During startup, the total output current consists of both the load current and the charge current of the output capacitor. For the FPF2700 and FPF2701; if the total output current exceeds the set current limit threshold (determined via RSET) for longer than the blanking time, the device may not be able to start properly. This imposes an upper limit to the value of the output capacitor, given the load current and the selected current limit value. COUT should not exceed the COUTmax calculated in Equation 2 or the switch does not start properly due to the set current limit: COUT max I LIM _ MIN 500s / V PD _ MAX ( NormalOperation )(VIN 12V ) (1 ) 2 0.140 140 mW If device is in over-current condition and VOUT>2V, power dissipation can be calculated as: If device is in short-circuit current limit and VOUT < 2V, power dissipation can be calculated as: 27< VIN ≤ 32 47 32< VIN ≤ 36 68 (7) PD = (VIN - VOUT) x (0.75 x ILIM (Max) ) Design Example: Using FPF2702 in a VIN = 5V application where ILIM (Max) = 2A, assuming VOUT = 2.5V; power dissipation across the switch is calculated as: PD = (5 - 2.5) x 2 = 5W COUT Selection Guide 22 (6) PD = (VIN - VOUT) x ILIM (Max) During a hard short condition on the output while operating at greater than 24V VIN, a large instantaneous inrush current is delivered to the shorted output. A capacitor must be placed at the OUTPUT pin, acting as a current source to support the instantaneous current draw (Table 2). A low-ESR capacitor is recommended. Once the value of the output capacitor is determined from Table 2, Equation 2 must be reevaluated. 24< VIN ≤ 27 (5) FPF2702 PD(Max) during OC: High-Voltage Operation (Output Capacitor) Capacitance (μF) TJ is junction temperature; PD is power dissipation on the switch; ΘJA is the thermal resistance, junction-to-ambient of the package; and TA is ambient temperature. Design Example For a 12V application and ILIM (Max) = 1A, maximum power dissipation in a normal operation is calculated as: (2) VIN (V) (4) where: A 0.1μF to 1μF capacitor, COUT, should be placed between the OUT and GND pins. This capacitor helps prevent parasitic board inductances from forcing the output voltage below ground when the switch turns off. This capacitor should have a low dissipation factor. An X7R Multilayer Ceramic Chip (MLCC) capacitor is recommended. © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 ( I LIM ( Max ) ) 2 R ON ( MAX The maximum junction temperature should be limited to Output Capacitor Table 2. ation ) (8) Whereas in a short-circuit current-limit condition (VOUT ≈ 0V), power dissipation is calculated as: PD = ((VIN - VOUT) x (0.75 x ILIM (Max)) = (5 - 0) x (0.75 x 2) = 7.5W (9) FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Input Capacitor www.fairchildsemi.com 14 For the best performance, all traces should be as short as possible. To be most effective, the input and output capacitors should be placed close to the device to minimize the effects that parasitic trace inductances may have on normal and short-circuit operation (Figure 42). Using wide traces for IN, OUT, and GND pins helps minimize parasitic electrical effects as well as the caseto-ambient thermal impedance. 3. The IN, OUT, and GND pins dissipate most of the heat generated during high-load current condition. The layout suggested in Figure 42 and Figure 43 is strongly recommended illustrating a proper layout for devices in MLP 3x3 packages. IN, OUT, and GND pins are connected to adequate copper so that heat may be transferred as efficiently as possible out of the device. The low-power FLAGB and ON pins traces may be laid-out diagonally from the device to maximize the area available to the ground pad. Place the input and output capacitors as close as possible to the device. To minimize the interference between analog ground (chip ground, pin 5) and power ground during load current excursion, the ground terminal of the input and output capacitors and the RSET resistor should be routed directly to chip ground and away from power ground. Improving Thermal Performance Improper layout could result in higher junction temperature and trigger thermal shutdown protection. This is particularly significant for the FPF2702, where the device operates in Constant Current Mode under overload conditions. During fault conditions, the power dissipation of the switch could exceed the maximum absolute power dissipation. The following techniques improve the thermal performance of this family of devices. These techniques are listed in order of the significance of their impact. Figure 42. Proper Layout of Output and Ground Copper Area (Top, SST, and AST Layers) 1. Thermal performance of the load switch can be improved by connecting the Die Attach Pad (DAP) of the MLP 3x3 package to the GND plane of the PCB. 2. Embedding two exposed through-hole vias into the DAP provides a path for heat to transfer to the back GND plane of the PCB. A drill size of round, 15 mils (0.4mm) with 1-ounce copper plating is recommended for appropriate solder reflow. A smaller-size hole prevents the solder from penetrating into the via, resulting in device lift-up. Similarly, a larger hole consumes excessive solder and may result in voiding the DAP. Figure 43. Proper Layout (Bottom and ASB Layers) Figure 41. Two Through-Hole Open Vias Embedded in the DAP © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches PCB Layout Recommendations www.fairchildsemi.com 15 layout recommendations section. Additional information about demonstration board can be found in the FPF270X board users guide. The FPF270X demonstration board has components and circuitry to demonstrate the load switch’s functions and features. Thermal performance of the board is improved using the techniques recommended in the Figure 44. Top, SST, and AST Layers Figure 45. Bottom and ASB Layers © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches FPF270x Demonstration Board www.fairchildsemi.com 16 5.00 4.80 A 0.65 3.81 5 8 B 6.20 5.80 PIN ONE INDICATOR 1.75 4.00 3.80 1 5.60 4 1.27 (0.33) 0.25 M 1.27 C B A LAND PATTERN RECOMMENDATION 0.25 0.10 SEE DETAIL A 1.75 MAX R0.10 0.10 0.51 0.33 0.50 x 45° 0.25 C OPTION A - BEVEL EDGE GAGE PLANE R0.10 8° 0° 0.90 0.406 0.25 0.19 C OPTION B - NO BEVEL EDGE 0.36 NOTES: UNLESS OTHERWISE SPECIFIED A) THIS PACKAGE CONFORMS TO JEDEC MS-012, VARIATION AA, ISSUE C, B) ALL DIMENSIONS ARE IN MILLIMETERS. C) DIMENSIONS DO NOT INCLUDE MOLD FLASH OR BURRS. D) LANDPATTERN STANDARD: SOIC127P600X175-8M. E) DRAWING FILENAME: M08AREV13 SEATING PLANE (1.04) DETAIL A SCALE: 2:1 Figure 46. 8-Lead, Small Outline Package (SOP) Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or obtain the most recent revision. Package specifications do not expand the terms of Fairchild’s worldwide terms and conditions, specifically the warranty therein, which covers Fairchild products. FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Physical Dimensions Always visit Fairchild Semiconductor’s online packaging area for the most recent package drawings: http://www.fairchildsemi.com/packaging/. © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 www.fairchildsemi.com 17 3.00 0.15 C A 2X 2.52 B 8 3.00 PIN1 IDENT 5 1.94 1.70 3.30 0.56 8X 0.15 C TOP VIEW 1 2X 0.65 4 0.47 8X RECOMMENDED LAND PATTERN 0.80 MAX 0.10 C (0.20) 0.08 C 0.05 0.00 NOTES: C SIDE VIEW A. PACKAGE CONFORMS TO JEDEC MO-229 EXCEPT WHERE NOTED. SEATING PLANE B. DIMENSIONS ARE IN MILLIMETERS. C. DIMENSIONS AND TOLERANCES PER ASME Y14.5M, 1994. 2.45 2.35 PIN 1 IDENT 1 (0.35) 4X D. LAND PATTERN RECOMMENDATION IS BASED ON FSC DESIGN ONLY. E. DRAWING FILENAME: MKT-MLP08Vrev1. 4 1.75 1.65 0.40 8X 0.30 8 0.10 0.05 5 C A B C 0.40 8X 0.30 0.65 BOTTOM VIEW Figure 1. 8-Lead, 3x3mm Molded Leadless Package (MLP) Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or obtain the most recent revision. Package specifications do not expand the terms of Fairchild’s worldwide terms and conditions, specifically the warranty therein, which covers Fairchild products. FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches Physical Dimensions Always visit Fairchild Semiconductor’s online packaging area for the most recent package drawings: http://www.fairchildsemi.com/packaging/. © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 www.fairchildsemi.com 18 FPF2700 / FPF2701 / FPF2702 — AccuPower™ 0.4~2A Adjustable Over-Current Protection Load Switches © 2010 Fairchild Semiconductor Corporation FPF2700 / FPF2701 / FPF2702 • Rev. 1.0.2 www.fairchildsemi.com 19