19-0329; Rev 0; 12/94 NUAL KIT MA ATION U EET L H A S V A E T WS DA FOLLO High-Accuracy, Low-Dropout Linear Regulators ____________________________Features ♦ Fixed Outputs: 3.3V (MAX687/MAX688) 3.0V (MAX689) ♦ Directly Drives External PNP Transistor ♦ 10mA Min Base-Current Drive for >1A Output ♦ Low Dropout Voltage: 100mV Dropout at 650mA Output (FZT749) 40mV Dropout at 200mA Output (FZT749) 0.8V Dropout at 4A Output ♦ Power-Fail Output Monitors the Output Voltage ♦ Automatic, Latched Shutdown when Output Falls Out of Regulation (MAX687) ♦ Precision Threshold Shutdown Control (MAX688/MAX689) ♦ Low Supply Current: 150µA Operating <1µA Shutdown ♦ 2.7V to 11.0V Supply Range ♦ 8-Pin DIP/SO/µMAX Packages ♦ <2mV Line Transient with 3.4V to 3.6V Input ♦ Output Accuracy <±2% ________________________Applications High-Efficiency Linear Regulator Battery-Powered Devices Portable Instruments Portable Telephones Power Supply or Backup Supply for Memory ______________Ordering Information PART TEMP. RANGE 0°C to +70°C 8 Plastic DIP MAX687CSA MAX687CUA MAX687EPA MAX687ESA 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C 8 SO 8 µMAX 8 Plastic DIP 8 SO Ordering Information continued at end of data sheet. __________Typical Operating Circuit Q1 FZT749 +3.5V to +5V INPUT 3.3V @ 500mA RB 12Ω __________________Pin Configuration TOP VIEW BASE BLIM OUT IN IN 1 (ON) SHDN 2 PFO 3 MAX687 MAX688 MAX689 GND 4 ( ) ARE FOR MAX687 DIP/SO/µMAX 8 CC 7 BASE 6 BLIM 5 OUT PIN-PACKAGE MAX687CPA C2 68µF C1 2.2µF ON MAX687 PFO POWER-FAIL OUTPUT CC ON GND GND C3 10nF ________________________________________________________________ Maxim Integrated Products Call toll free 1-800-998-8800 for free samples or literature. 1 MAX687/MAX688/MAX689 _______________General Description The MAX687/MAX688/MAX689 low-dropout linear regulators operate with an input-to-output voltage differential limited only by an external PNP transistor. Outputs are fixed at 3.3V (MAX687/MAX688) or 3.0V (MAX689). The only external components required are a PNP pass transistor and output, compensation, and bypass capacitors. Base drive to the external transistor is at least 10mA, permitting output currents to exceed 1A when using high-gain transistors (β > 100). Output current limiting is implemented by limiting the external transistor’s base current. Output voltage monitoring and shutdown functions are included. The 3.3V MAX687 automatically shuts down whenever the output voltage drops below 2.96V. An internal power-fail comparator also monitors the output and provides an early warning of low output voltage before the device shuts down. When shut down, the output is latched off until the ON input is pulsed. Turning off the power supply in this way prevents battery damage due to excessive discharge or cell-reversal. Typical applications include portable telephones and other battery-powered equipment where the power supply must be disabled when the battery voltage is low. The MAX688 and MAX689 do not have an automatic shutdown function, and are identical except for their output voltages. Each device has an active-low shutdown-control input, used to turn its output on or off at any time. As SHDN falls, the device enters a standby mode before fully shutting down. When in standby, the reference and comparators are fully operational, permitting the transition from normal mode to standby mode to occur at a precise voltage level on SHDN. MAX687/MAX688/MAX689 High-Accuracy, Low-Dropout Linear Regulators ABSOLUTE MAXIMUM RATINGS Input Supply Voltage IN to GND ............................................12V Terminal Voltages to GND PFO (MAX687) ........................................-0.3V to VOUT + 0.3V PFO (MAX688/MAX689) ......................................-0.3V to 12V All Remaining Pins .....................................-0.3V to VIN + 0.3V PFO Sink Current ...............................................................10mA PFO Source Current (MAX687)...........................................10mA Continuous Power Dissipation (TA = +70°C) Plastic DIP (derate 9.09mW/°C above +70°C) ............727mW SO (derate 5.88mW/°C above +70°C) .........................471mW µMAX (derate 4.1mW/°C above +70°C) ......................330mW Operating Temperature Ranges MAX68_C_A .......................................................0°C to +70°C MAX68_E_A ....................................................-40°C to +85°C Storage Temperature Range .............................-65°C to +165°C Lead Temperature (soldering, 10sec) .............................+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 = 3.8V, SHDN = VIN (MAX688/MAX689), RB = 0Ω, C1 = 2.2µF, C2 = 10µF, C3 = 10nF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 11.0 V LINEAR REGULATOR Supply Voltage VIN (Note 1) MAX687/MAX688 Output Voltage VOUT MAX689 Dropout Voltage (Note 2) 2.7 VIN = 3.8V, IBASE = 1mA 3.2 3.3 3.4 3.8V ≤ VIN ≤ 11.0V, 1µA ≤ IBASE ≤ 10mA 3.13 3.3 3.47 VIN = 3.5V, IBASE = 1mA 2.9 3.0 3.1 3.5V ≤ VIN ≤ 11.0V, 1µA ≤ IBASE ≤ 10mA 2.85 3.0 3.15 VIN - VOUT PNP = FZT749, ILOAD = 200mA, C2 = 20µF 40 MAX687/MAX688 0.4 1.4 MAX689 3.5V ≤ VIN ≤ 11.0V, IBASE = 1mA 0.4 1.4 45 60 On 150 250 Standby, MAX688/MAX689 11 25 mV/V 1µA ≤ IBASE ≤ 10mA Load Regulation Supply Current IGND VIN = 3.8V, PNP = FZT749, no load BASE Sink Current IBASE VBASE = VIN - 1V Shutdown Base-Current Limit RB is connected from BASE to BLIM (Ω), RB = 0Ω to 100Ω Start-Up Time (Note 3) 10 2 < 0.02 1 20 40 PNP = FZT749, ILOAD = 100mA (Note 4) µA mA mA 300 µs 2 C2 mV 70 100 130 RB + 5Ω RB + 5Ω RB + 5Ω Start-Up Overshoot Load Capacitance mV 3.8V ≤ VIN ≤ 11.0V, IBASE = 1mA Line Regulation V 10 _______________________________________________________________________________________ % µF High-Accuracy, Low-Dropout Linear Regulators (VIN = 3.8V, SHDN = VIN (MAX688/MAX689), RB = 0Ω, C1 = 2.2µF, C2 = 10µF, C3 = 10nF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 110 170 mV 7 mV 70 mV MAX687: ON, PFO, SHDN PFO Threshold Voltage Below VNOM (Note 5) VNOM VPFT Falling VOUT, comparators monitor VOUT PFO Hysteresis Shutdown Threshold Voltage Below VPFT VPFT - VSD Falling VOUT, comparators monitor VOUT Shutdown Threshold Voltage VSD Falling VOUT, comparators monitor VOUT PFO Output Voltage High VOH ISOURCE = 50µA, part on, VIN = 2.7V PFO Output Voltage Low VOL ISINK = 1.2mA, VIN = 2.7V VIH Output turns on VIL Output remains off ON Threshold Voltage 20 2.96 V VOUT - 0.3 V 0.06 0.3 V 1.0 V 0.2 ON Input Leakage Current 0.2 100 nA MAX688/MAX689: SHDN, PFO PFO Threshold Voltage MAX688 3.07 3.13 3.19 MAX689 2.77 2.85 2.89 VPFT Falling VOUT, comparators monitor VOUT VSON On, SHDN falling 1.25 VSSY Standby 1.0 VSSD Shutdown PFO Hysteresis 7 SHDN Threshold Voltages Rising SHDN, standby→on V SHDN = 1.23V PFO, SHDN Transient Rejection Glitch immunity 100 ISINK = 1.2mA, VIN = 2.7V 0.06 PFO Off Leakage Current Output Noise Voltage 70 -25 mV 25 V PFO = 11V, V SHDN > 1.25V en V 0.2 SHDN Input Current VOL mV 1.2 SHDN Hysteresis PFO Output Voltage Low V 10Hz ≤ f ≤ 10kHz, ILOAD = 200mA 66 10Hz ≤ f ≤ 1MHz, ILOAD = 200mA 105 nA µs 0.3 V 1 µA µVRMS Note 1: Minimum VIN for regulated VOUT depends on the characteristics of the external PNP transistor, and on the load. The reference and comparators are functional down to the minimum voltage specified, but the output may not be in regulation. Note 2: Dropout voltage is defined as VIN - VOUT when VOUT is 50mV below its value at VIN = VNOM + 1V. Note 3: The start-up time specification is the time taken from ON or SHDN rising to BASE sinking current. VOUT rise time is longer and is a function of load capacitance, C2, and load resistance, RL. Note 4: Minimum load capacitance is a function of RL. Minimum C2 = 10µF for loads up to 100mA and 1µF/10mA for higher loads. ESR of C2 should be no larger than 1/100 of RL. Guaranteed by design. Note 5: The nominal output voltage, VNOM, is defined under the default conditions of testing: VIN = 3.8V, IBASE = 1mA, TA = TMIN to TMAX. _______________________________________________________________________________________ 3 MAX687/MAX688/MAX689 ELECTRICAL CHARACTERISTICS (continued) __________________________________________Typical Operating Characteristics (Circuits of Figures 1 and 2, VIN = 5V, Q1 = FZT749, TA = +25°C, unless otherwise noted.) 3.31219 OUTPUT VOLTAGE (V) 3.30862 3.30505 3.30149 3.29792 3.29435 3.30800 3.30576 3.30352 3.30128 3.29904 3.29679 3.29455 3.29231 3.29007 3.28783 3.29078 3.28722 3.28365 50 100 150 NUMBER OF UNITS 200 50 100 150 NUMBER OF UNITS 250 Q1 = 2N2907 RB = 0Ω 0.9 0.10 0.6 0.5 0.4 0.3 0.2 OBSERVE MAXIMUM POWER DISSIPATION LIMIT OF EXTERNAL PASS TRANSISTOR. 600 1000 1400 MAX687/9-03 4 3 2 1 0 0 0 1800 200 600 400 1000 800 0 200 400 600 800 1000 1200 LOAD CURRENT (mA) LOAD CURRENT (mA) LOAD CURRENT (mA) GND CURRENT vs. DROPOUT VOLTAGE GND CURRENT vs. DROPOUT VOLTAGE NO-LOAD SUPPLY CURRENT vs. TEMPERATURE 4 3 300mA LOAD 2 4 3 300mA LOAD 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 VIN - VOUT (V) 140 138 136 134 132 130 100mA LOAD 1 10mA LOAD 0 MAX687/9-9 142 5 2 100mA LOAD 144 SUPPLY CURRENT (µA) 5 6 GND CURRENT (mA) 6 146 MAX687/9-8 7 MAX687/9-7 7 250 0.1 0 200 200 6 GND CURRENT (mA) 0.15 150 5 0.7 0.20 100 GND CURRENT vs. LOAD CURRENT 0.8 0 50 0 NUMBER OF UNITS 1.0 MAX687/9-05 Q1 = FZT749 RB = 0Ω VIN - VOUT (V) VIN - VOUT (V) 200 DROPOUT VOLTAGE vs. LOAD CURRENT 0.30 0.05 3.00023 2.99848 2.99674 2.99150 2.98975 DROPOUT VOLTAGE vs. LOAD CURRENT 0.25 3.00198 2.99499 2.99324 0 250 3.01071 3.00896 3.00721 3.00547 3.00372 MAX687/9-06 0 4 3.01595 3.01420 3.01245 MAX687/9-5 OUTPUT VOLTAGE (V) 3.31576 3.32145 3.31920 3.31696 3.31472 3.31248 3.31024 OUTPUT VOLTAGE (V) 3.31932 MAX687/9-01 MAX687/9-02 3.32289 1 MAX689 OUTPUT VOLTAGE DISTRIBUTION MAX688 OUTPUT VOLTAGE DISTRIBUTION MAX687 OUTPUT VOLTAGE DISTRIBUTION GND CURRENT (mA) MAX687/MAX688/MAX689 High-Accuracy, Low-Dropout Linear Regulators 128 10mA LOAD 126 0 0 1 2 3 4 5 VIN - VOUT (V) 6 7 8 -55 -25 0 25 50 75 TEMPERATURE (°C) _______________________________________________________________________________________ 100 125 High-Accuracy, Low-Dropout Linear Regulators 3.310 0.1500 0.1000 3.305 3.300 3.295 3.290 0.0500 3.285 0 3.280 VIN = 4.3V Min ILOAD = 20mA 70 RIPPLE REJECTION (dB) 0.2000 80 MAX687/9-11 MAX687/9-10 0.2500 MAX687/MAX688 RIPPLE REJECTION vs. FREQUENCY 3.315 OUTPUT VOLTAGE (V) SHUTDOWN SUPPLY CURRENT (µA) 0.3000 OUTPUT VOLTAGE vs. TEMPERATURE MAX687/9-16 SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE 60 VIN = 3.6V Min ILOAD = 200mA 50 40 30 20 10 C2 = 20µF -55 -25 0 25 50 75 100 125 0 -55 -25 TEMPERATURE (°C) 0 25 50 75 TEMPERATURE (°C) 100 VIN 3.6V 100k VIN 5V/div VOUT 1V/div VIN 3.4V ILOAD = 200mA C1 = 2.2µF C2 = 20µF C3 = 10nF 2ms/div SHDN 5V/div ILOAD = 500mA C1 = 2.2µF C2 = 68µF C3 = 10nF LOAD-TRANSIENT RESPONSE 1ms/div LOAD-TRANSIENT RESPONSE VOUT 3.3V 10mV/div VOUT 3.3V 10mV/div 500mA 500mA ILOAD 200mA/div ILOAD 200mA/div 0mA 100µs/div 1k 10k FREQUENCY (Hz) VIN 3.6V VIN 3.4V VIN = 3.4V 100 VOUT 3.3V 1mV/div VOUT 3.3V 1mV/div 2ms/div 10 MAX687/MAX688 POWER-UP AND EXIT FROM SHUTDOWN LINE-TRANSIENT RESPONSE LINE-TRANSIENT RESPONSE ILOAD = 70mA C1 = 2.2µF C2 = 20µF C3 = 10nF 125 0mA VIN = 3.5V 100µs/div _______________________________________________________________________________________ 5 MAX687/MAX688/MAX689 ____________________________Typical Operating Characteristics (continued) (Circuits of Figures 1 and 2, VIN = 5V, Q1 = FZT749, TA = +25°C, unless otherwise noted.) MAX687/MAX688/MAX689 High-Accuracy, Low-Dropout Linear Regulators ______________________________________________________________Pin Description PIN NAME 1 IN FUNCTION Positive input voltage, 2.7V to 11.0V ON (MAX687) ON activates the regulator when pulsed high. In order for the regulator to remain on, ON must remain high until VOUT exceeds the internal shutdown threshold voltage. The MAX687 is shut down when VOUT < 2.96V, and remains latched off until ON is pulsed high. When powered up, the MAX687 does not start up until ON is pulsed high. Connect to VIN if not used. 2 SHDN (MAX688/ MAX689) SHDN is a three-level input that controls the mode of operation. The device is on when V SHDN > 1.25V. The output is disabled and the supply current is reduced (IIN < 25µA, standby mode) when V SHDN < 1.2V, and is fully off (IIN < 1µA, shutdown mode) when V SHDN < 0.2V. Connect SHDN to IN if the shutdown function is not used. PFO is low when SHDN is low (below 0.2V). 3 PFO Power-Fail Output. PFO trips when VOUT is 170mV below nominal VOUT at IBASE = 1mA. PFO sources and sinks current in the MAX687, but is an open drain in the MAX688/MAX689. When shut down, PFO is always low and sinks current. Leave PFO open if not used. 4 GND Ground 5 OUT Regulator Output. MAX687/MAX688, 3.3V; MAX689, 3.0V. 6 BLIM Base current limit. A resistor (RB) connected between BASE and BLIM sets the maximum base drive to the PNP transistor: IBASE ≤ 0.1V / (RB + 5Ω). This limits quiescent current rise during dropout and also provides current limiting without using a current-sense resistor in the collector of the external PNP, thus not impacting dropout. Output current limiting accuracy depends on how well the external PNP beta (hFE) is controlled. Connect to BASE if not used. 7 BASE Base drive for the external PNP transistor. Current limiting is controlled using a resistor (RB) connected between BASE and BLIM. For maximum output current, connect BASE to BLIM. 8 CC 2 Compensation Capacitor. Connect a non-polarized capacitor (10nF to 100nF) from CC to GND. _______________Detailed Description The MAX687/MAX688/MAX689 are precision lowdropout linear regulators employing external PNP transistors to achieve a wide range of output currents at voltages of 3.0V or 3.3V. The maximum base current for the PNP can be limited using a resistor. Limiting the base drive keeps high currents from being wasted when the device is in dropout (e.g., at low input voltages), and limits the regulator’s output current. The dropout voltage is limited only by the PNP transistor’s VCE(SAT). The Power-Fail Output (PFO) goes low when the output voltage drops 170mV below the nominal level. The three devices differ in their output voltages, in their shutdown-control functions, and in PFO’s output drive (see Table 1). 6 Table 1. Device Functions FUNCTION MAX687 MAX688 MAX689 VOUT 3.3V 3.3V 3.0V Shutdown Control Automatic at low VOUT. Latched. Use ON to start. External SHDN External SHDN PFO Sources & Sinks Open Drain Open Drain The MAX687’s output voltage is internally monitored; a falling VOUT is signaled by PFO going low. As the output falls further, the MAX687 automatically enters a lowpower shutdown mode, where the base drive to the external PNP is cut off. PFO trips at a minimum of 110mV below the nominal VOUT, and shutdown occurs by 2.96V. PFO is guaranteed to trip before the device _______________________________________________________________________________________ High-Accuracy, Low-Dropout Linear Regulators Q1 FZT749 +5V INPUT 3.3V @ 500mA 70mV of hysteresis between the standby and on states prevents chatter between the two modes. The voltage applied to the SHDN pin can be derived from a resistive divider from VIN. When VSHDN is less than 1.2V, the output is off. The device is fully shut down (<1µA) when SHDN is pulled below 200mV. SHDN is not latched, and as SHDN is raised, the MAX688/MAX689 exit shutdown and enter the standby mode. At the higher SHDN threshold, the output is turned on. Figure 1 shows a typical circuit for the MAX687, and Figure 2 shows the same circuit configured for the MAX688/MAX689. The accuracy of the output current limit depends on accurate knowledge of the PNP pass transistor’s current gain (hFE). With RB = 12Ω, BLIM limits base current to 6mA (IBASE = 0.1V / (RB + 5Ω)). See BaseCurrent Limiting section. The PFO comparators on all three devices, and the internal shutdown comparator on the MAX687, reject high-speed spikes (<100µs). This reduces the PFO output’s noise sensitivity, and stops the MAX687 from being shut down inadvertently when there is noise on the input supply. _______________Transistor Selection Specifications The PNP pass transistor must meet specifications for • current gain, • power dissipation, and • collector current. The hFE influences the maximum output current the circuit can deliver. The largest guaranteed output current +5V INPUT RB 12Ω BASE C4 0.1µF BASE OUT POWER FAIL PFO ON CC GND C3 10nF C1 2.2µF ON / OFF R2 100k BLIM OUT IN C2 68µF MAX687 C1 2.2µF R1 10kΩ RB 12Ω BLIM IN 3.3V/ 3.0V @ 500mA Q1 FZT749 MAX688 MAX689 SHDN GND C2 68µF PFO POWER FAIL CC C3 10nF GND ON CAN BE DRIVEN DIRECTLY FROM LOGIC WHEN R1 AND C4 ARE NOT USED. Figure 1. MAX687 Operating Circuit GND Figure 2. MAX688/MAX689 Operating Circuit _______________________________________________________________________________________ 7 MAX687/MAX688/MAX689 shuts down. Once the MAX687 is shut down, it can only be turned on again when (a) the ON pin is pulsed high, and (b) the conditions that triggered shutdown have changed (e.g., the load has been reduced or the input voltage has increased). In order for the MAX687 to latch into its on state, the ON pulse must remain high until the output voltage has risen above the shutdown threshold. The internal shutdown can be used to prevent deep discharge of a battery, for example, to provide “self backup” of CMOS RAM or to protect the battery itself. The RC circuit attached to the ON input in Figure 1 achieves automatic start-up at power-on by delivering a brief pulse whenever the input voltage is suddenly applied. This circuit is not suitable for applications where the input voltage rises slowly. The RC values should be chosen to keep ON high until the output rises above about 3.13V. The values shown in Figure 1 for C4 and R1 (0.1µF and 10kΩ) are suitable for most applications. To ensure start-up when the input voltage is very close to the circuit’s dropout voltage, when the circuit is used to drive a very large capacitive load, or for high-power circuits (ILOAD > 3A), increase the value of R1 to increase the ON pulse width. The 3.3V MAX688 and the 3.0V MAX689 incorporate the same PFO warning whenever V OUT droops. However, the MAX688/MAX689 do not automatically shut down when the output voltage drops even further. Instead, the SHDN input controls external shutdown. As SHDN is pulled low, the chip first enters a low-current standby state (<25µA). The threshold at which standby mode is entered is precisely controlled (±2%) so the output can be turned off at a well-defined point. MAX687/MAX688/MAX689 High-Accuracy, Low-Dropout Linear Regulators is given by ILOAD(MAX) = 10mA x hFE(MIN). The transistor’s rated power dissipation must exceed the actual power dissipated in the transistor. The power dissipated (PD) equals the maximum load current (ILOAD(MAX)) times the maximum input to output voltage differential: PD = ILOAD(MAX) x (VIN(MAX) - VOUT). The rated transistor collector current must exceed the maximum load current. Suitable transistors include the Zetex FZT749, and the 2N2907A (see Table 2). Base-Current Limiting A comparator monitors the voltage across the external base-current-limiting resistor (between BASE and BLIM). This sets the maximum base current. If BASE and BLIM are shorted, base current is limited nominally to 20mA due to an internal 5Ω resistor in series with the external resistance. Choose the base-current-limiting resistor, R B , so the drop across it at rated load is approximately 50mV. RB = (50mV) x hFE(MIN) ILOAD(MAX) − 5Ω The base drive is controlled so the voltage on BLIM is limited to 100mV below the voltage on BASE; with a 50mV nominal drop across RB + 5Ω, base-current drive is limited to twice the nominal. This limits base current when the external PNP is heavily saturated, such as when the regulator is in dropout due to low input voltage. In addition, if the external PNP’s hFE is defined within reasonable limits, base-current control effectively limits output current without a dropout voltage penalty. ________________Capacitor Selection Bypass Capacitor (C1) Connect a bypass capacitor from IN to GND. 4.7µF makes the circuit insensitive to layout, and is sufficient for any load. Smaller values may be used—down to 0.33µF—with low-ESR capacitors, good board layout, and a low-impedance incoming supply. 8 Connect the bypass capacitor directly between pins 1 and 4 of the IC, using short leads. Connect the emitter of the PNP transistor directly to the bypass capacitor using a very short trace. Output Capacitor (C2) The output filter capacitor must be at least 10µF. For currents above 100mA, use 1µF of capacitance for every 10mA of load current (e.g., 20µF for 200mA load, 50µF for 500mA). Low-ESR capacitors give best stability and transient response. Ensure that the capacitor’s ESR is less than 1% of the load resistance. See Table 2 for a list of manufacturers. Sanyo OS-CON capacitors are recommended for applications operating at temperatures below 0°C. Compensation Capacitor (C3) Connect a compensation capacitor from CC to GND. 10nF is recommended, although higher values (up to 100nF) may also be used. Higher C3 values eliminate power-on overshoot, but extend power-up times. Current flowing into or out of CC causes the regulator’s reference voltage to change, resulting in shifted output voltage and trip thresholds. Use non-polarized capacitors (e.g., ceramic, polyester, etc.) to keep leakage currents below 25nA. Aluminum and tantalum electrolytic capacitors are unsuitable because of their high leakage currents. __________________Power-Fail Output The PFO output trips when VOUT is 170mV below nominal VOUT at IBASE = 1mA. PFO sources and sinks current in the MAX687, but is an open drain in the MAX688/MAX689 and only sinks current. When shut down, PFO is always low regardless of the voltage at OUT. Leave PFO open if it is not used. _______________________________________________________________________________________ High-Accuracy, Low-Dropout Linear Regulators DROPOUT VOLTAGE vs. LOAD CURRENT High-Power Output Circuit MAX687/9-04 1.0 Q1 = TIP42 Q2 = 2N4403 BASE = BLIM 0.9 0.8 VIN - VOUT (V) Figure 3 shows a pseudo-Darlington transistor configuration to increase load-current capability and maintain a low dropout voltage with a 4A load. A heatsink must be added when high power is dissipated in the pass transistor. Figure 4 shows the (VIN - VOUT) voltage required to maintain regulation for different load currents. Figure 5 shows an oscilloscope plot of the transient response of a 200mA to 4A load step. MAX687/MAX688/MAX689 __________Applications Information 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 1000 2000 3000 4000 LOAD CURRENT (mA) Q1 T1P42 +5V INPUT 3.3V/ 3.0V @ 4A Q2 2N4403 LOAD-TRANSIENT RESPONSE 1kΩ 10Ω BASE IN C1 220µF ON / OFF Figure 4. Dropout Voltage vs. Load Current of Figure 3 C2 470µF x3 MAX688 MAX689 SHDN GND VOUT +3.3V, 20mV/div R2 100kΩ BLIM OUT PFO IOUT 1A/div POWER FAIL CC C3 10nF 50µs/div Figure 3. 4A Low-Dropout Circuit Figure 5. Transient Response for a 200mA to 4A Load Step Using Circuit of Figure 3 _______________________________________________________________________________________ 9 MAX687/MAX688/MAX689 High-Accuracy, Low-Dropout Linear Regulators Table 2a. Component Suppliers DEVICE MANUFACTURER PRODUCTION METHOD CAPACITORS 267 series Matsuo F95 Tantalum series Nichicon Surface Mount Table 2b. Manufacturers’ Phone and Fax Numbers MANUFACTURER COUNTRY Central Semiconductor USA (516) 435-1110 (516) 435-1824 Matsuo USA (714) 969-2491 (714) 960-6492 Motorola USA (602) 244-3370 (602) 244-4015 USA (708) 843-7500 (708) 843-2798 TELEPHONE FAX 595 Tantalum series Sprague OS-CON series low-ESR organic semiconductor Sanyo LXF series United Chemi-Con Through-Hole Nichicon Japan BIPOLAR TRANSISTORS ZTX749 Zetex T1P42 Motorola 2N4403 Motorola USA Sanyo Japan Through-Hole 2N2907A Motorola CMPT2907A Central Semiconductor PZT2907AT1 Motorola FZT749 Zetex 10 Surface Mount +81-7-52318461 +81-7-52564158 (619) 661-6835 (619) 661-1055 +81-7-20706306 +81-7-20701174 Sprague USA (603) 224-1961 (603) 224-1430 United Chemi-Con USA (714) 255-9500 (714) 255-9400 USA (516) 543-7100 (516) 864-7630 Zetex UK +44-61-6275105 ______________________________________________________________________________________ +44-61-6275467 High-Accuracy, Low-Dropout Linear Regulators PART TEMP. RANGE MAX687/MAX688/MAX689 _Ordering Information (continued) PIN-PACKAGE MAX688CPA 0°C to +70°C 8 Plastic DIP MAX688CSA MAX688CUA MAX688EPA MAX688ESA MAX689CPA 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C 0°C to +70°C 8 SO 8 µMAX 8 Plastic DIP 8 SO 8 Plastic DIP MAX689CSA MAX689CUA MAX689EPA MAX689ESA 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C 8 SO 8 µMAX 8 Plastic DIP 8 SO ______________________________________________________________________________________ 11 MAX687/MAX688/MAX689 High-Accuracy, Low-Dropout Linear Regulators ________________________________________________________Package Information DIM C α A 0.101mm 0.004 in e B A1 E L A A1 B C D E e H L α INCHES MAX MIN 0.044 0.036 0.008 0.004 0.014 0.010 0.007 0.005 0.120 0.116 0.120 0.116 0.0256 0.198 0.188 0.026 0.016 6° 0° MILLIMETERS MIN MAX 0.91 1.11 0.10 0.20 0.25 0.36 0.13 0.18 2.95 3.05 2.95 3.05 0.65 4.78 5.03 0.41 0.66 0° 6° H 8-PIN µMAX MICROMAX SMALL OUTLINE PACKAGE D 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. 12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 1994 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.