EVALUATION KIT MANUAL FOLLOWS DATA SHEET High-Accuracy, Low-Dropout Linear Regulators PART MAX687CUA MAX687ESA MAX687EPA. +3.

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1 19-39; Rev ; 1/94 EALUATION KIT MANUAL FOLLOWS DATA SHEET High-Accuracy, Low-Dropout General Description The low-dropout linear regulators operate with an input-to-output voltage differential limited only by an external PNP transistor. Outputs are fixed at 3.3 (MAX687/MAX688) or 3. (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 1mA, permitting output currents to exceed 1A when using high-gain transistors (β > 1). Output current limiting is implemented by limiting the external transistor s base current. Output voltage monitoring and shutdown functions are included. The 3.3 MAX687 automatically shuts down whenever the output voltage drops below.96. 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. Applications High-Efficiency Linear Regulator Battery-Powered Devices Portable Instruments Portable Telephones Power Supply or Backup Supply for Memory Pin Configuration Features Fixed Outputs: 3.3 (MAX687/MAX688) 3. (MAX689) Directly Drives External PNP Transistor 1mA Min Base-Current Drive for >1A Output Low Dropout oltage: 1m Dropout at 65mA Output (FZT749) 4m Dropout at ma Output (FZT749).8 Dropout at 4A Output Power-Fail Output Monitors the Output oltage Automatic, Latched Shutdown when Output Falls Out of Regulation (MAX687) Precision Threshold Shutdown Control (MAX688/MAX689) Low Supply Current: 15µA Operating <1µA Shutdown.7 to 11. Supply Range 8-Pin DIP/SO/µMAX Packages <m Line Transient with 3.4 to 3.6 Input Output Accuracy <±% Ordering Information PART MAX687CPA MAX687CSA MAX687CUA MAX687EPA MAX687ESA Ordering Information continued at end of data sheet. Typical Operating Circuit +3.5 to +5 INPUT TEMP. RANGE C to +7 C C to +7 C C to +7 C -4 C to +85 C -4 C to +85 C Q1 FZT749 R B 1Ω PIN-PACKAGE 8 Plastic DIP 8 SO 8 µmax 8 Plastic DIP 8 SO 5mA TOP IEW IN (ON) SHDN PFO ( ) ARE FOR MAX MAX687 MAX688 MAX689 DIP/SO/µMAX CC BASE BLIM OUT C1.µF ON IN ON BASE MAX687 BLIM OUT PFO CC C 68µF C3 1nF POWER-FAIL OUTPUT Maxim Integrated Products 1 Call toll free for free samples or literature.

2 ABSOLUTE MAXIMUM RATINGS Input Supply oltage IN to...1 Terminal oltages to PFO (MAX687) to OUT +.3 PFO (MAX688/MAX689) to 1 All Remaining Pins to IN +.3 PFO Sink Current...1mA PFO Source Current (MAX687)...1mA 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 Continuous Power Dissipation (T A = +7 C) Plastic DIP (derate 9.9mW/ C above +7 C)...77mW SO (derate 5.88mW/ C above +7 C)...471mW µmax (derate 4.1mW/ C above +7 C)...33mW Operating Temperature Ranges MAX68_C_A... C to +7 C MAX68_E_A...-4 C to +85 C Storage Temperature Range C to +165 C Lead Temperature (soldering, 1sec)...+3 C ( IN = 3.8, SHDN = IN (MAX688/MAX689), R B = Ω, C1 =.µf, C = 1µF, C3 = 1nF, T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +5 C.) PARAMETER LINEAR REGULATOR Supply oltage Output oltage Dropout oltage (Note ) Line Regulation Load Regulation Supply Current BASE Sink Current SYMBOL IN OUT IN - OUT I I BASE (Note 1) MAX687/MAX688 MAX689 1µA I BASE 1mA IN = 3.8, PNP = FZT749, no load BASE = IN - 1 CONDITIONS IN = 3.8, I BASE = 1mA 3.8 IN 11., 1µA I BASE 1mA IN = 3.5, I BASE = 1mA 3.5 IN 11., 1µA I BASE 1mA PNP = FZT749, I LOAD = ma, C = µf MAX687/MAX688 MAX IN 11., I BASE = 1mA 3.5 IN 11., I BASE = 1mA On Standby, MAX688/MAX689 Shutdown MIN TYP MAX < UNITS m m/ m 11 5 µa ma Base-Current Limit R B is connected from BASE to BLIM (Ω), R B = Ω to 1Ω R B + 5Ω R B + 5Ω R B + 5Ω ma Start-Up Time (Note 3) 3 µs Start-Up Overshoot % Load Capacitance C PNP = FZT749, I LOAD = 1mA (Note 4) 1 µf

3 ELECTRICAL CHARACTERISTICS (continued) ( IN = 3.8, SHDN = IN (MAX688/MAX689), R B = Ω, C1 =.µf, C = 1µF, C3 = 1nF, T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +5 C.) PARAMETER MAX687: ON, PFO, SHDN PFO Threshold oltage Below NOM (Note 5) PFO Hysteresis Shutdown Threshold oltage Below PFT Shutdown Threshold oltage PFO Output oltage High PFO Output oltage Low ON Threshold oltage ON Input Leakage Current MAX688/MAX689: SHDN, PFO PFO Threshold oltage PFO Hysteresis SHDN Threshold oltages SHDN Hysteresis SHDN Input Current PFO, SHDN Transient Rejection PFO Output oltage Low PFO Off Leakage Current Output Noise oltage SYMBOL NOM - PFT PFT - SD SD OH OL IH IL CONDITIONS Falling OUT, comparators monitor OUT Falling OUT, comparators monitor OUT Falling OUT, comparators monitor OUT I SOURCE = 5µA, part on, IN =.7 I SINK = 1.mA, IN =.7 MIN TYP MAX OUT Output turns on 1. Output remains off.. 1 PFT Falling OUT, comparators monitor OUT MAX MAX SON On, SHDN falling 1.5 SSY Standby SSD Shutdown. Rising SHDN, standby on 7 SHDN = Glitch immunity 1 OL I SINK = 1.mA, IN = PFO = 11, SHDN > e n 1Hz f 1kHz, I LOAD = ma 66 1Hz f 1MHz, I LOAD = ma UNITS m m m na m m na µs µa µ RMS Note 1: Minimum IN for regulated OUT 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 : Dropout voltage is defined as IN - OUT when OUT is 5m below its value at IN = NOM + 1. Note 3: The start-up time specification is the time taken from ON or SHDN rising to BASE sinking current. OUT rise time is longer and is a function of load capacitance, C, and load resistance, R L. Note 4: Minimum load capacitance is a function of R L. Minimum C = 1µF for loads up to 1mA and 1µF/1mA for higher loads. ESR of C should be no larger than 1/1 of R L. Guaranteed by design. Note 5: The nominal output voltage, NOM, is defined under the default conditions of testing: IN = 3.8, I BASE = 1mA, T A = T MIN to T MAX. 3

4 Typical Operating Characteristics (Circuits of Figures 1 and, IN = 5, Q1 = FZT749, T A = +5 C, unless otherwise noted.) OUTPUT OLTAGE () IN - OUT () MAX687 OUTPUT OLTAGE DISTRIBUTION NUMBER OF UNITS Q1 = FZT749 R B = Ω DROPOUT OLTAGE vs. LOAD CURRENT.5 OBSERE MAXIMUM POWER DISSIPATION LIMIT OF EXTERNAL PASS TRANSISTOR LOAD CURRENT (ma) MAX687/9- MAX687/9-5 OUTPUT OLTAGE () IN - OUT () MAX688 OUTPUT OLTAGE DISTRIBUTION NUMBER OF UNITS Q1 = N97 R B = Ω DROPOUT OLTAGE vs. LOAD CURRENT MAX687/ LOAD CURRENT (ma) MAX687/9-5 OUTPUT OLTAGE () CURRENT (ma) MAX689 OUTPUT OLTAGE DISTRIBUTION NUMBER OF UNITS CURRENT vs. LOAD CURRENT LOAD CURRENT (ma) MAX687/9-6 MAX687/9-3 CURRENT (ma) CURRENT vs. DROPOUT OLTAGE 3mA LOAD 1mA LOAD 1mA LOAD IN - OUT () MAX687/9-7 CURRENT (ma) CURRENT vs. DROPOUT OLTAGE 3mA LOAD 1mA LOAD IN - OUT () 1mA LOAD MAX687/9-8 SUPPLY CURRENT (µa) NO-LOAD SUPPLY CURRENT vs. TEMPERATURE TEMPERATURE ( C) MAX687/9-9 4

5 Typical Operating Characteristics (continued) (Circuits of Figures 1 and, IN = 5, Q1 = FZT749, T A = +5 C, unless otherwise noted.) SHUTDOWN SUPPLY CURRENT (µa) SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE TEMPERATURE ( C) LINE-TRANSIENT RESPONSE MAX687/9-1 OUT 3.3 1m/div OUTPUT OLTAGE () OUTPUT OLTAGE vs. TEMPERATURE TEMPERATURE ( C) LINE-TRANSIENT RESPONSE MAX687/9-11 OUT 3.3 1m/div RIPPLE REJECTION (db) MAX687/MAX688 RIPPLE REJECTION vs. FREQUENCY IN = 3.6 Min I LOAD = ma C = µf IN = 4.3 Min I LOAD = ma 1 1 1k 1k 1k FREQUENCY (Hz) MAX687/MAX688 POWER-UP AND EXIT FROM SHUTDOWN MAX687/9-16 IN 5/div IN 3.6 IN 3.4 IN 3.6 IN 3.4 OUT 1/div SHDN 5/div I LOAD = 7mA C1 =.µf C = µf C3 = 1nF ms/div I LOAD = ma C1 =.µf C = µf C3 = 1nF ms/div I LOAD = 5mA C1 =.µf C = 68µF C3 = 1nF 1ms/div LOAD-TRANSIENT RESPONSE LOAD-TRANSIENT RESPONSE OUT 3.3 1m/div OUT 3.3 1m/div 5mA 5mA I LOAD ma/div I LOAD ma/div ma ma IN = 3.4 1µs/div IN = 3.5 1µs/div 5

6 Pin Description PIN NAME 1 IN Positive input voltage,.7 to 11. ON (MAX687) SHDN (MAX688/ MAX689) 3 PFO 4 Ground FUNCTION ON activates the regulator when pulsed high. In order for the regulator to remain on, ON must remain high until OUT exceeds the internal shutdown threshold voltage. The MAX687 is shut down when OUT <.96, 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 IN if not used. SHDN is a three-level input that controls the mode of operation. The device is on when SHDN > 1.5. The output is disabled and the supply current is reduced (I IN < 5µA, standby mode) when SHDN < 1., and is fully off (I IN < 1µA, shutdown mode) when SHDN <.. Connect SHDN to IN if the shutdown function is not used. PFO is low when SHDN is low (below.). Power-Fail Output. PFO trips when OUT is 17m below nominal OUT at I BASE = 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. 5 OUT Regulator Output. MAX687/MAX688, 3.3; MAX689, BLIM Base current limit. A resistor (R B) connected between BASE and BLIM sets the maximum base drive to the PNP transistor: I BASE.1 / (R B + 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 (h FE) is controlled. Connect to BASE if not used. 7 BASE Base drive for the external PNP transistor. Current limiting is controlled using a resistor (R B) connected between BASE and BLIM. For maximum output current, connect BASE to BLIM. 8 CC Compensation Capacitor. Connect a non-polarized capacitor (1nF to 1nF) from CC to. Detailed Description The are precision lowdropout linear regulators employing external PNP transistors to achieve a wide range of output currents at voltages of 3. or 3.3. 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 CE(SAT). The Power-Fail Output (PFO) goes low when the output voltage drops 17m 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). Table 1. Device Functions FUNCTION MAX687 MAX688 MAX689 OUT Shutdown Control Automatic at low OUT. 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 OUT 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 11m below the nominal OUT, and shutdown occurs by.96. PFO is guaranteed to trip before the device 6

7 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 The values shown in Figure 1 for C4 and R1 (.1µF and 1kΩ) 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 3.3 MAX688 and the 3. MAX689 incorporate the same PFO warning whenever 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 (<5µA). The threshold at which standby mode is entered is precisely controlled (±%) so the output can be turned off at a well-defined point. 7m 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 IN. When SHDN is less than 1., the output is off. The device is fully shut down (<1µA) when SHDN is pulled below m. 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 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 = 1Ω, BLIM limits base current to 6mA (IBASE =.1 / (RB + 5Ω)). See Base- Current Limiting section. The PFO comparators on all three devices, and the internal shutdown comparator on the MAX687, reject high-speed spikes (<1µs). 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 h FE influences the maximum output current the circuit can deliver. The largest guaranteed output current +5 INPUT Q1 FZT749 5mA +5 INPUT Q1 FZT / 5mA C4.1µF C1.µF R1 1kΩ R B 1Ω BASE BLIM IN OUT ON MAX687 PFO CC C 68µF C3 1nF POWER FAIL ON CAN BE DRIEN DIRECTLY FROM LOGIC WHEN R1 AND C4 ARE NOT USED. Figure 1. MAX687 Operating Circuit C1.µF ON / OFF IN BASE SHDN R B 1Ω MAX688 MAX689 BLIM CC OUT PFO C3 1nF Figure. MAX688/MAX689 Operating Circuit C 68µF R 1k POWER FAIL 7

8 is given by ILOAD(MAX) = 1mA 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 (IN(MAX) - OUT). The rated transistor collector current must exceed the maximum load current. Suitable transistors include the Zetex FZT749, and the N97A (see Table ). 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 ma due to an internal 5Ω resistor in series with the external resistance. Choose the base-current-limiting resistor, RB, so the drop across it at rated load is approximately 5m. ( 5m ) x hfe(min) R B = 5Ω ILOAD(MAX) The base drive is controlled so the voltage on BLIM is limited to 1m below the voltage on BASE; with a 5m 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. 4.7µF makes the circuit insensitive to layout, and is sufficient for any load. Smaller values may be used down to.33µf with low-esr capacitors, good board layout, and a low-impedance incoming supply. 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 (C) The output filter capacitor must be at least 1µF. For currents above 1mA, use 1µF of capacitance for every 1mA of load current (e.g., µf for ma load, 5µF for 5mA). 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 for a list of manufacturers. Sanyo OS-CON capacitors are recommended for applications operating at temperatures below C. Compensation Capacitor (C3) Connect a compensation capacitor from CC to. 1nF is recommended, although higher values (up to 1nF) 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 5nA. Aluminum and tantalum electrolytic capacitors are unsuitable because of their high leakage currents. Power-Fail Output The PFO output trips when OUT is 17m below nominal OUT 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. 8

9 Applications Information High-Power Output Circuit 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 (IN - OUT) voltage required to maintain regulation for different load currents. Figure 5 shows an oscilloscope plot of the transient response of a ma to 4A load step. +5 INPUT ON / OFF 1kΩ C1 µf Q1 T1P4 Q N443 IN BASE SHDN 1Ω MAX688 MAX689 BLIM OUT PFO CC C3 1nF 3.3/ 4A C 47µF x3 POWER FAIL R 1kΩ IN - OUT () DROPOUT OLTAGE vs. LOAD CURRENT Q1 = TIP4 Q = N443 BASE = BLIM LOAD CURRENT (ma) Figure 4. Dropout oltage vs. Load Current of Figure 3 LOAD-TRANSIENT RESPONSE MAX687/9-4 OUT +3.3, m/div I OUT 1A/div 5µs/div Figure 3. 4A Low-Dropout Circuit Figure 5. Transient Response for a ma to 4A Load Step Using Circuit of Figure 3 9

10 Table a. Component Suppliers DEICE CAPACITORS 67 series Matsuo F95 Tantalum series MANUFACTURER Nichicon 595 Tantalum series Sprague OS-CON series low-esr organic Sanyo semiconductor LXF series United Chemi-Con BIPOLAR TRANSISTORS ZTX749 T1P4 N443 N97A CMPT97A PZT97AT1 FZT749 Zetex Motorola Motorola Motorola Central Semiconductor Motorola Zetex PRODUCTION METHOD Surface Mount Through-Hole Through-Hole Surface Mount Table b. Manufacturers Phone and Fax Numbers MANU- FACTURER Central Semiconductor COUNTRY TELEPHONE FAX USA (516) (516) Matsuo USA (714) (714) Motorola USA (6) (6) Nichicon Sanyo USA (78) (78) Japan USA (619) (619) Japan Sprague USA (63) (63) United Chemi-Con Zetex USA (714) (714) USA (516) (516) UK

11 _Ordering Information (continued) PART TEMP. RANGE PIN-PACKAGE MAX688CPA MAX688CSA MAX688CUA C to +7 C C to +7 C C to +7 C 8 Plastic DIP 8 SO 8 µmax MAX688EPA -4 C to +85 C 8 Plastic DIP MAX688ESA -4 C to +85 C 8 SO MAX689CPA C to +7 C 8 Plastic DIP MAX689CSA MAX689CUA C to +7 C C to +7 C 8 SO 8 µmax MAX689EPA -4 C to +85 C 8 Plastic DIP MAX689ESA -4 C to +85 C 8 SO 11

12 Package Information e D B E A A1 H.11mm.4 in C L α DIM A A1 B C D E e H L α 8-PIN µmax MICROMAX SMALL OUTLINE PACKAGE MIN INCHES.56 MAX MILLIMETERS MIN MAX 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. 1 Maxim Integrated Products, 1 San Gabriel Drive, Sunnyvale, CA 9486 (48) Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.