19-2664; Rev 1; 4/03 50mA/100mA Current-Limit Switches Applications PDAs and Palmtop Devices Cell Phones Features ♦ Guaranteed Current Limit: 50mA, 100mA ♦ Thermal-Shutdown Protection ♦ Reverse-Current Protection ♦ 0.7Ω On-Resistance ♦ 14ms Guaranteed Blanking Time ♦ FLAG Function (MAX4785/MAX4787) ♦ 65µA Supply Current ♦ 8µA Latch-Off Current (MAX4785/MAX4787) ♦ 0.01µA Shutdown Current ♦ 2.3V to 5.5V Supply Range ♦ Undervoltage Lockout ♦ Fast Current-Limit Response Time ♦ Tiny SC70 Package Ordering Information PART TEMP RANGE PINPACKAGE TOP MARK MAX4785EXS-T -40°C to +85°C 4 SC70-4 MAX4785EXK-T -40°C to +85°C 5 SC70-5 AGE ADL MAX4786EXS-T -40°C to +85°C 4 SC70-4 AGF MAX4787EXS-T -40°C to +85°C 4 SC70-4 AGG MAX4787EXK-T -40°C to +85°C 5 SC70-5 AND MAX4788EXS-T -40°C to +85°C 4 SC70-4 AGH Selector Guide appears at end of data sheet. GPS Systems Typical Operating Circuit Hand-Held Devices 2.3V TO 5.5V Pin Configurations TOP VIEW IN ON OUT 1 GND 2 5 IN OUT 1 MAX4785 MAX4787 MAX4785– MAX4788 4 ON FLAG 3 4 IN GND 2 MAX4785 MAX4787 µP FLAG TO EXTERNAL PORT OUT 3 ON GND SC70 SC70 ________________________________________________________________ Maxim Integrated Products 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. 1 MAX4785–MAX4788 General Description The MAX4785–MAX4788 family of switches feature internal current limiting to prevent host devices from being damaged due to faulty load conditions. These analog switches have a low 0.7Ω on-resistance and operate from a 2.3V to 5.5V input voltage range. They are available with guaranteed 50mA and 100mA current limits, making them ideal for load-switching applications. When the switch is on and a load is connected to the port, a guaranteed blanking time of 14ms ensures that the transient voltages settle down. If after this blanking time the load current is greater than the current limit, the MAX4785 and MAX4787 enter a latch-off state where the switch is turned off and FLAG is issued to the microprocessor. The switch can be turned on again by cycling the power or the ON pin. The MAX4786 and MAX4788 have an autoretry feature where the switch turns off after the blanking time and then continuously checks to see if the overload condition is present. The switch remains on after the overload condition disappears. The MAX4785 and MAX4787 are available in a tiny space-saving 4-pin or 5-pin SC70 package. The MAX4786 and MAX4788 are available only in the 4-pin SC70 package. For higher current current-limiting switches, refer to the MAX4789–MAX4794 and MAX1693 data sheets. MAX4785–MAX4788 50mA/100mA Current-Limit Switches ABSOLUTE MAXIMUM RATINGS IN, ON, FLAG, OUT to GND .....................................-0.3V to +6V OUT Short Circuit to GND .................................Internally Limited Continuous Power Dissipation (TA = +70°C) 4-Pin SC70 (derate 3.1mW/°C above +70°C) ..............245mW 5-Pin SC70 (derate 3.1mW/°C above +70°C) ..............247mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+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 = 2.3V to 5.5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VIN = 3.3V, TA = +25°C.) (Note 1) PARAMETER SYMBOL Operating Voltage VIN Quiescent Current IQ CONDITIONS VON = VIN, IOUT = 0, VIN = 2.3V to 5.0V switch on VIN = 5.0V to 5.5V ILATCH VON = VIN, after an overcurrent fault (MAX4785/MAX4787) Shutdown Current ISHDN VON = 0V IFWD Reverse Current Limit IREV ON Input Leakage Undervoltage Lockout 65 UNITS 5.5 V 100 120 8 0.01 µA 1 µA 120 MAX4787/MAX4788 100 240 MAX4785/MAX4786 120 MAX4787/MAX4788 240 -1 Rising edge 0.01 1.8 Undervoltage Lockout Hysteresis RON ON Input Logic High Voltage VIH ON Input Logic Low Voltage VIL TA = +25°C, IOUT = 20mA 0.7 1 µA ISINK = 1mA (MAX4785/MAX4787) FLAG Output High Leakage Current VIN = V F LAG = 5.5V (MAX4785/MAX4787) V mV 1 1.3 2.0 FLAG Output Logic Low Voltage mA µA 2.2 TA = -40°C to +85°C, IOUT = 20mA mA +1 100 On-Resistance µA 15 50 VON = 0V, VOUT = 0V UVLO MAX MAX4785/MAX4786 VON = VIN or GND Off Switch Leakage TYP 2.3 Latch-Off Current (Note 2) Forward Current Limit MIN Ω V 0.8 V 0.4 V 1 µA Thermal Shutdown 150 °C Thermal-Shutdown Hysteresis 15 °C DYNAMIC Turn-On Time (Note 3) ON from low to high; IOUT = 10mA, CL = 0.1µF 50 µs Turn-Off Time (Note 3) ON from high to low; IOUT = 10mA, CL = 0.1µF 30 ns 2 _______________________________________________________________________________________ 50mA/100mA Current-Limit Switches (VIN = 2.3V to 5.5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VIN = 3.3V, TA = +25°C.) (Note 1) PARAMETER SYMBOL Blanking Time CONDITIONS tBLANK MIN Overcurrent fault, Figures 2, 3 Short-Circuit Current-Limit Response Time TYP 14 VON = VIN = 3.3V, short circuit applied to OUT Retry Time (Note 4) UNITS 60 ms 5 MAX4786/MAX4788: overcurrent fault, Figure 2 tRETRY MAX µs 98 420 ms Note 1: All parts are 100% tested at +25°C. Limits across the full temperature range are guaranteed by design and correlation. Note 2: Latch-off current does not include the current flowing into FLAG. Note 3: The on-time is defined as the time taken for the current through the switch to go from 0mA to full load. The off-time is defined as the time taken for the current through the switch to go from full load to 0mA. Note 4: Retry time is typically 7x the blanking time. Typical Operating Characteristics (VIN = 3.3V, TA = +25°C, unless otherwise noted.) SUPPLY CURRENT vs. TEMPERATURE 80 60 50 40 30 70 60 VIN = 3.3V 50 40 30 20 20 10 10 0 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -15 10 35 60 85 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 VON = VIN VIN = 5V VIN = 3.3V -40 -15 10 35 60 SUPPLY VOLTAGE (V) TEMPERATURE (°C) TEMPERATURE (°C) SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE SHUTDOWN LEAKAGE CURRENT vs. TEMPERATURE LATCH-OFF LEAKAGE CURRENT vs. TEMPERATURE 0.1 0.01 0.001 -15 10 35 TEMPERATURE (°C) 60 85 VIN = 5V 0.1 0.01 VIN = 3.3V 0.001 0.0001 -40 85 MAX4785 toc06 1 100 LATCH-OFF LEAKAGE CURRENT (nA) 1 10 MAX4785-05 MAX4785-04 10 -40 -40 6.0 SHUTDOWN LEAKAGE CURRENT (nA) 2.0 SHUTDOWN SUPPLY CURRENT (nA) VIN = 5V LATCH-OFF (µA) SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) 70 VON = VIN MAX4785-02 VON = VIN 80 90 MAX4785-01 90 LATCH-OFF CURRENT vs. TEMPERATURE MAX4785 toc03 QUIESCENT SUPPLY CURRENT vs. SUPPLY VOLTAGE 10 1 VIN = 5V 0.1 VIN = 3.3V 0.01 0.001 0.0001 -15 10 35 TEMPERATURE (°C) 60 85 -40 -15 10 35 60 85 TEMPERATURE (°C) _______________________________________________________________________________________ 3 MAX4785–MAX4788 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (VIN = 3.3V, TA = +25°C, unless otherwise noted.) NORMALIZED ON-RESISTANCE vs. TEMPERATURE OUTPUT CURRENT vs. OUTPUT VOLTAGE 250 OUTPUT CURRENT (mA) 0.8 0.6 0.4 150 100 MAX4785/MAX4786 50 0.2 0 0 -40 -15 10 35 60 85 VIN - VOUT (V) SWITCH TURN-ON/OFF TIMES vs. TEMPERATURE FLAG-BLANKING TIMEOUT vs. TEMPERATURE VCC = 3.3V 45 FLAG-BLANKING TIME (ms) ILOAD = 10mA VCC = 5V 0.1 OFF 0.01 50 MAX4785 toc09 ON 1 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3 TEMPERATURE (°C) 100 10 MAX4787/MAX4788 200 MAX4785 toc10 NORMALIZED RON 1.0 MAX4785 toc08 VCC = 3.3V 1.2 300 MAX4785-07 1.4 TURN-ON/OFF TIMES (µs) MAX4785–MAX4788 50mA/100mA Current-Limit Switches 40 35 30 25 0.001 -40 -15 10 35 60 20 85 -40 TEMPERATURE (°C) 10 35 60 CURRENT-LIMIT RESPONSE MAX4785 toc11 VIN = 3.3V CIN = 1µF MAX4785 toc12 VIN 2V/div VIN = VON 1V/div VON 2V/div IOUT 100mA/div 40µs/div 4 85 TEMPERATURE (°C) CURRENT-LIMIT RESPONSE COUT = 1µF -15 VIN = VON CIN = 1µF COUT = 1µF 20µs/div _______________________________________________________________________________________ IOUT 100mA/div 50mA/100mA Current-Limit Switches CURRENT-LIMIT RESPONSE (OUT SHORTED TO GND) SWITCH TURN-ON TIME RESPONSE MAX4785 toc13 CIN = 1µF COUT = 1µF MAX4785 toc14 VIN = 3.3V VIN 2V/div VON VOUT 2V/div IOUT 10mA/div IOUT 2A/div 40µs/div 100µs/div FLAG-BLANKING RESPONSE SWITCH TURN-OFF TIME RESPONSE MAX4785 toc16 MAX4785 toc15 VIN = 3.3V VON 2V/div VIN 2V/div VON 2V/div FLAG 2V/div IOUT 10mA/div IOUT 100mA/div 4ms/div 100ns/div Pin Description PIN NAME FUNCTION SC70 SC70 1 1 OUT Switch Output. Bypass with a 0.1µF capacitor to ground. 2 2 GND Ground — 3 FLAG Fault Output. This open-drain output goes low when the device stays in forward or reverse current limit for more than the blanking time period. FLAG is high impedance when a fault is not present or when ON is low. 3 4 ON Active-High Switch-On Input. A logic high turns the switch on. 4 5 IN Input. Bypass with a 0.1µF ceramic capacitor to ground. _______________________________________________________________________________________ 5 MAX4785–MAX4788 Typical Operating Characteristics (continued) (VIN = 3.3V, TA = +25°C, unless otherwise noted.) MAX4785–MAX4788 50mA/100mA Current-Limit Switches REVERSE-CURRENT DETECTOR MAX4785/MAX4787 ONLY FLAG BLANKING TIME CIRCUITRY N FORWARD CURRENT DETECTOR N IN ON UNDERVOLTAGE LOCKOUT OUT +2.0V LOGIC GND AUTORETRY MAX4785–MAX4788 Figure 1. MAX4785–MAX4788 Functional Diagram Detailed Description The MAX4785–MAX4788 are forward/reverse currentlimited switches that operate from a 2.3V to 5.5V input voltage range and guarantee a 50mA and 100mA minimum current-limit threshold for different options. The voltage drop across an internal sense resistor is compared to two reference voltages to indicate a forward or reverse current-limit fault. When the load current exceeds the preset current limit for greater than the fault-blanking time, the switch opens. The MAX4786 and MAX4788 have an autoretry function that turns on the switch again after an internal retry time expires. If the faulty load condition is still present after the blanking time, the switch turns off again and the cycle is repeated. If the faulty load condition is not present, the switch remains on. The MAX4785 and MAX4787 do not have the autoretry option and the switch remains in latch-off mode until the ON pin or the input power is cycled from high to low and then high again. The undervoltage lockout (UVLO) circuit prevents erroneous switch operation when the input voltage goes too low during startup conditions. 6 Reverse-Current Protection The MAX4785–MAX4788 limit the reverse current (VOUT to VIN) from exceeding the maximum IREV value. The switch is shut off and FLAG is asserted (MAX4785/ MAX4787) if the reverse current-limit condition persists for more than the blanking time. This feature prevents excessive reverse currents from flowing through the device. Switch-On/Off Control Toggle ON high to enable the current-limited switches. The switches are continuously on, only if VIN exceeds the UVLO threshold (typically 2V) and there is no fault. When a forward/reverse current fault is preset or the die exceeds the thermal-shutdown temperature of +150°C, OUT is internally disconnected from IN and the supply current decreases to 8µA (latch off). The switch is now operating in one of its off states. The switch off-state also occurs when driving ON low, thus reducing the supply current (shutdown) to 0.01µA. Table 1 illustrates the ON/OFF state of the MAX4785–MAX4788 currentlimit switches. _______________________________________________________________________________________ 50mA/100mA Current-Limit Switches ON FAULT Low X OFF Shutdown High Undervoltage lockout OFF Shutdown High Thermal High Current limit SWITCH ON/OFF SUPPLY CURRENT MODE OFF immediately (tBLANK period does not apply) Latch off OFF after tBLANK period has elapsed Latch off ON during tBLANK period, OFF during tRETRY period for the MAX4786 and MAX4788; cycle repeats until fault is removed See the Autoretry section FLAG Indicator The MAX4785 and MAX4787 feature a latched fault output, FLAG. Whenever a fault is activated, it latches FLAG output low and also turns the switch off. FLAG is an open-drain output transistor and requires an external pullup resistor from FLAG to IN. During shutdown (ON is low), the pulldown on FLAG output is released in order to limit power dissipation. FLAG goes low when any of the following conditions occur: • The die temperature exceeds the thermal-shutdown temperature limit of +150°C. • The device is in current limit for more than the faultblanking period. • VIN is below UVLO threshold. Autoretry (MAX4786/MAX4788) When the forward or reverse current-limit threshold is exceeded, tBLANK timer begins counting (Figure 2). The timer resets if the overcurrent condition disappears before tBLANK has elapsed. A retry time delay, tRETRY, is started immediately after tBLANK has elapsed and during that time, the switch is latched off. At the end of tRETRY, the switch is turned on again. If the fault still exists, the cycle is repeated. If the fault has been removed, the switch stays on. The autoretry feature saves system power in the case of an overcurrent or short-circuit condition. During tBLANK, when the switch is on, the supply current is at the current limit. During tRETRY, when the switch is off, the current through the switch is zero. Instead of observing the full load current, the switch sees the equivalent load current times duty cycle or ISUPPLY = I LOAD ✕ t BLANK /(t BLANK + t RETRY ). With a typical tBLANK = 37ms and typical tRETRY = 259ms, the duty cycle is 12%, which results in an 88% power savings over the switch being on the entire time. The duty cycle is consistent across the process and devices. Latch Off (MAX4785/MAX4787) When the forward or reverse current-limit threshold is exceeded, tBLANK timer begins counting. The timer tBLANK tRETRY tBLANK tBLANK CURRENT LIMIT LOAD CURRENT SHORT CONDITION REMOVED ON SWITCH STATUS OFF Figure 2. MAX4786/MAX4788 Autoretry Fault Blanking Diagram resets if the overcurrent condition disappears before tBLANK has elapsed. The switch is shut off if the overcurrent condition continues up to the end of the blanking time. Reset the switch by either toggling ON (Figure 3a) or cycling the input voltage below UVLO, typically 2V (Figure 3b). Fault Blanking The MAX4785–MAX4788 feature 14ms (min) fault blanking. Fault blanking allows current-limit faults, including momentary short-circuit faults that occur when hot swapping a capacitive load, and also ensures that no fault is issued during power-up. When a load transient causes the device to enter current limit, an internal counter starts. If the load-transient fault persists beyond the fault-blanking timeout, the MAX4785 and MAX4787s’ FLAG asserts low. Load-transient faults less than tBLANK do not cause a FLAG output assertion. Only current-limit faults are blanked. A thermal fault and input voltage drops below the UVLO threshold cause FLAG to assert immediately and do not wait for the blanking time. Thermal Shutdown The MAX4785–MAX4788 have a thermal shutdown feature to protect the devices from overheating. The switch turns off and FLAG goes low immediately (no fault blanking) when the junction temperature exceeds +150°C. _______________________________________________________________________________________ 7 MAX4785–MAX4788 Table 1. MAX4785–MAX4788 Switch Truth Table MAX4785–MAX4788 50mA/100mA Current-Limit Switches tBLANK the MAX4785–MAX4788 from tripping erroneously. If the load capacitance is too large, then current may not have enough time to charge the capacitance and the device assumes that there is a faulty load condition. The maximum capacitive load value that can be driven from OUT is obtained by the following formula: tBLANK LOAD CURRENT ON SWITCH STATUS CMAX < OFF ON PIN VOLTAGE Layout and Thermal Dissipation To optimize the switch response time to output shortcircuit conditions, it is very important to keep all traces as short as possible to reduce the effect of undesirable parasitic inductance. Place input and output capacitors as close as possible to the device (no more than 5mm). IN and OUT pins must be connected with short traces to the power bus. During normal operation, the power dissipation is small and the package temperature change is minimal. If the output is continuously shorted to ground at the maximum supply voltage, the operation of the switches with the autoretry option does not cause problems because the total power dissipated during the short is scaled by the duty cycle: FLAG PIN STATUS (a) tBLANK tBLANK LOAD CURRENT ON SWITCH STATUS IN PIN VOLTAGE IFWD _ MIN × tBLANK _ MIN VIN OFF UVLO PMAX = FLAG PIN STATUS VIN _ MAX × IOUT _ MAX × tBLANK = 161mW tRETRY + tBLANK where VIN = 5.5V, IOUT = 240mA, tBLANK = 14ms, and tRETRY = 98ms. (b) Figure 3. MAX4785/MAX4787 Latch Off Fault Blanking The switches with autoretry feature turn back on when the device temperature drops approximately 15°C. The switches with latchoff feature require ON cycling. Attention must be given to the MAX4785 and MAX4787 where the latch-off condition must be manually reset by toggling ON from high to low. If the latch-off time duration is not sufficiently high, it is possible for the device to reach the thermal-shutdown threshold and never be able to turn the device on until it cools down. Applications Information Selector Guide Input Capacitor To limit the input voltage drop during momentary output short-circuit conditions, connect a capacitor from IN to GND. A 0.1µF ceramic capacitor is adequate for most applications; however, higher capacitor values further reduce the voltage drop at the input and are recommended for lower voltage applications. Output Capacitance Connect a 0.1µF capacitor from OUT to GND. This capacitor helps prevent inductive parasitics from pulling OUT negative during turn-off, thus preventing 8 PART CURRENT LIMIT (mA) FLAG FUNCTION AUTORETRY MAX4785EXS 50 No No MAX4785EXK 50 Yes No MAX4786EXS 50 No Yes MAX4787EXS 100 No No MAX4787EXK 100 Yes No MAX4788EXS 100 No Yes _______________________________________________________________________________________ 50mA/100mA Current-Limit Switches SC70, 4L.EPS Chip Information TRANSISTOR COUNT: 1659 PROCESS: BiCMOS _______________________________________________________________________________________ 9 MAX4785–MAX4788 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.) Package Information (continued) (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.) SC70, 5L.EPS MAX4785–MAX4788 50mA/100mA Current-Limit Switches 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. 10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.