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_______________General Description The MAX764/MAX765/MAX766 inverting switching regu- lators are highly efficient over a wide range of load cur- rents, delivering up to 1.5W. A unique, current-limited, pulse-frequency-modulated (PFM) control scheme com- bines the benefits of traditional PFM converters with the benefits of pulse-width-modulated (PWM) converters. Like PWM converters, the MAX764/MAX765/MAX766 are highly efficient at heavy loads. Yet because they are PFM devices, they use less than 120µA of supply current (vs. 2mA to 10mA for a PWM device). The input voltage range is 3V to 16V. The output volt- age is preset at -5V (MAX764), -12V (MAX765), or -15V (MAX766); it can also be adjusted from -1V to -16V using two external resistors (Dual ModeTM). The maxi- mum operating VIN - VOUT differential is 20V. These devices use miniature external components; their high switching frequencies (up to 300kHz) allow for less than 5mm diameter surface-mount magnetics. A stan- dard 47µH inductor is ideal for most applications, so no magnetics design is necessary. An internal power MOSFET makes the MAX764/MAX765/ MAX766 ideal for minimum component count, low- and medium-power applications. For increased output drive capabil i ty or higher output voltages, use the MAX774/MAX775/MAX776 or MAX1774, which drive an external power P-channel MOSFET for loads up to 5W. ________________________Applications LCD-Bias Generators Portable Instruments LAN Adapters Remote Data-Acquisition Systems Battery-Powered Applications ____________________________Features ' High Efficiency for a Wide Range of Load Currents ' 250mA Output Current ' 120µA Max Supply Current ' 5µA Max Shutdown Current ' 3V to 16V Input Voltage Range ' -5V (MAX764), -12V (MAX765), -15V (MAX766), or Adjustable Output from -1V to -16V ' Current-Limited PFM Control Scheme ' 300kHz Switching Frequency ' Internal, P-Channel Power MOSFET ______________Ordering Information Ordering Information continued on last page. * Dice are tested at TA = +25°C, DC parameters only. **Contact factory for availability and processing to MIL-STD-883. M A X 7 6 4 /M A X 7 6 5 /M A X 7 6 6 -5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ DC-DC Inverters ________________________________________________________________ Maxim Integrated Products 1 1 2 3 4 8 7 6 5 LX V+ V+ GNDREF SHDN FB OUT MAX764 MAX765 MAX766 DIP/SO TOP VIEW __________________Pin Configuration GND MAX764 SHDN LX OUT ON/OFF REF 47µH OUTPUT -5V INPUT 3V TO 15V V+ FB __________Typical Operating Circuit Call toll free 1-800-998-8800 for free samples or literature. 19-0176; Rev 0; 6/94 PART MAX764CPA MAX764CSA MAX764C/D 0°C to +70°C 0°C to +70°C 0°C to +70°C TEMP. RANGE PIN-PACKAGE 8 Plastic DIP 8 SO Dice* MAX764EPA MAX764ESA -40°C to +85°C -40°C to +85°C 8 Plastic DIP 8 SO MAX764MJA -55°C to +125°C 8 CERDIP** MAX765CPA MAX765CSA MAX765C/D 0°C to +70°C 0°C to +70°C 0°C to +70°C 8 Plastic DIP 8 SO Dice* MAX765EPA MAX765ESA -40°C to +85°C -40°C to +85°C 8 Plastic DIP 8 SO MAX765MJA -55°C to +125°C 8 CERDIP** Eval uatio n Kit Avai lable M A X 7 6 4 /M A X 7 6 5 /M A X 7 6 6 -5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ DC-DC Inverters 2 _______________________________________________________________________________________ ABSOLUTE MAXIMUM RATINGS ELECTRICAL CHARACTERISTICS (V+ = 5V, ILOAD = 0mA, CREF = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°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. V+ to GND..............................................................-0.3V to +17V OUT to GND ...........................................................+0.5V to -17V Maximum Differential (V+ to OUT) ......................................+21V REF, SHDN, FB to GND ...............................-0.3V to (V+ + 0.3V) LX to V+..................................................................+0.3V to -21V LX Peak Current ...................................................................1.5A 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 CERDIP (derate 8.00mW/°C above +70°C) .................640mW Operating Temperature Ranges MAX76_C_A ........................................................0°C to +70°C MAX76_E_A .....................................................-40°C to +85°C MAX76_MJA ..................................................-55°C to +125°C Maximum Junction Temperatures MAX76_C_A/E_A ..........................................................+150°C MAX76_MJA .................................................................+175°C Storage Temperature Range ............................-65°C to +160°C Lead Temperature (soldering, 10sec) ............................+300°C 3V ≤ V+ ≤ 16V V+ = 16V, SHDN = 0V or V+ V+ = 16V, SHDN < 0.4V 4V ≤ V+ ≤ 6V 0mA ≤ ILOAD ≤ 100mA MAX76_M 3V ≤ V+ ≤ 16V MAX76_C/E 0µA ≤ IREF ≤ 100µA MAX76_M MAX765C/E, -11.52V ≤ VOUT ≤ 12.48V MAX764, -4.8V ≤ VOUT ≤ 5.2V MAX76_E MAX76_C MAX76_M MAX76_E V+ = 16V, SHDN > 1.6V V+ = 10V, SHDN > 1.6V 3V ≤ V+ ≤ 16V MAX766, -14.40V ≤ VOUT ≤ -15.60V MAX76_C MAX765M, -11.52V ≤ VOUT ≤ 12.48V CONDITIONS V1.6VIHSHDN Input Voltage High µA±1SHDN Leakage Current 80 %/V0.12Line Regulation (Note 2) %/mA0.008Load Regulation (Note 2) µV/V40 100REF Line Regulation 4 15 mV 4 10 REF Load Regulation 1.4550 1.5 1.5450 1.4625 1.5 1.5375 V 1.4700 1.5 1.5300 VREFReference Voltage 35 105 50 120 µA 90 120ISSupply Current 3.5 V+ V 3.0 16.0 V+ Input Voltage Range 68 120 mA 150 260 IOUT Output Current and Voltage (Note 1) ±90 ±70 2 ISHDNShutdown Current 1 5 mV-10 10FB Trip Point nA ±50 IFBFB Input Current UNITSMIN TYP MAXSYMBOLPARAMETER MAX76_C/E MAX76_M VOUT = -5V 82VOUT = -15V Efficiency (Note 2) 10mA ≤ ILOAD ≤ 100mA, VIN = 5V % 3V ≤ V+ ≤ 16V V0.4VILSHDN Input Voltage Low M A X 7 6 4 /M A X 7 6 5 /M A X 7 6 6 -5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ DC-DC Inverters _______________________________________________________________________________________ 3 Note 1: See Maximum Output Current vs. Supply Voltage graph in the Typical Operating Characteristics. Guarantees are based on correlation to switch on-time, switch off-time, on-resistance, and peak current rating. Note 2: Circuit of Figure 2. ELECTRICAL CHARACTERISTICS (continued) (V+ = 5V, ILOAD = 0mA, CREF = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) IVOUTI + (V+) ‡ 10V ILXI + (V+) ≤ 20V IVOUTI + (V+) ‡ 10V CONDITIONS µs1.8 2.3 2.8tOFFMinimum Switch Off-Time µs12 16 20tONMaximum Switch On-Time A0.5 0.75IPEAKPeak Current at LX ±30 ±10 µA ±5 LX Leakage Current Ω1.4 2.5LX On-Resistance UNITSMIN TYP MAXSYMBOLPARAMETER MAX76_C MAX76_E MAX76_M __________________________________________Typical Operating Characteristics (V+ = 5V, VOUT = -5V, TA = +25°C, unless otherwise noted.) 100 0 0.1 10 1000 MAX764 EFFICIENCY vs. LOAD CURRENT M AX 76 4- 01 LOAD CURRENT (mA) EF FI CI EN CY (% ) 90 80 70 60 50 40 30 20 10 1 100 CIRCUIT OF FIGURE 2 VOUT = -5V ±4% V+ = 5V V+ = 10V V+ = 15V 100 0 0.1 10 1000 MAX765 EFFICIENCY vs. LOAD CURRENT M AX 76 4- 02 LOAD CURRENT (mA) EF FI CI EN CY (% ) 90 80 70 60 50 40 30 20 10 1 100 V+ = 8V V+ = 5V CIRCUIT OF FIGURE 2 VOUT = -12V ±4% 100 0 0.1 10 1000 MAX766 EFFICIENCY vs. LOAD CURRENT M AX 76 4- 03 LOAD CURRENT (mA) EF FI CI EN CY (% ) 90 80 70 60 50 40 30 20 10 1 100 V+ = 5V CIRCUIT OF FIGURE 2 VOUT = -15V ±4% M A X 7 6 4 /M A X 7 6 5 /M A X 7 6 6 -5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ DC-DC Inverters 4 _______________________________________________________________________________________ ____________________________Typical Operating Characteristics (continued) (V+ = 5V, VOUT = -5V, TA = +25°C, unless otherwise noted.) 0 -60 SHUTDOWN CURRENT vs. TEMPERATURE M AX 76 4 -0 7 TEMPERATURE (°C) SH UT DO W N CU RR EN T (µ A) -40 -20 0 20 40 60 80 100 120 140 V+ = 15V 0.5 1.0 1.5 2.0 2.5 3.0 4.0 3.5 V+ = 8V V+ = 4V 15.0 -60 MAXIMUM SWITCH ON-TIME vs. TEMPERATURE M AX 76 4 -0 8 TEMPERATURE (°C) M AX IM UM S W IT CH O N- TI M E (µ s) -40 -20 0 20 40 60 80 100 120 140 V+ = 15V V+ = 5V 15.2 15.4 15.6 15.8 16.0 16.2 16.4 16.6 16.8 17.0 2.20 -60 MINIMUM SWITCH OFF-TIME vs. TEMPERATURE M AX 76 4 -0 9 TEMPERATURE (°C) M IN IM UM S W IT CH O FF -T IM E (µ s) -40 -20 0 20 40 60 80 100 120 140 2.25 2.30 2.35 2.40 2.45 2.50 2.60 2.55 V+ = 5V V+ = 15V 6.2 -60 SWITCH ON/OFF-TIME RATIO vs. TEMPERATURE M AX 76 4 -1 0 TEMPERATURE (°C) SW IT CH O N/ OF F- TI M E RA TI O (µ s/ µs ) -40 -20 0 20 40 60 80 100 120 140 V+ = 5V 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7.0 7.1 7.2 0 START-UP SUPPLY VOLTAGE vs. OUTPUT CURRENT M AX 76 4 -1 1 OUTPUT CURRENT (mA) ST AR T- UP S UP PL Y VO LT AG E (V ) 0 1 2 3 4 5 6 8 7 50 100 150 200 250 300 CIRCUIT OF FIGURE 2 10,000 1 20 LX LEAKAGE CURRENT vs. TEMPERATURE 10 100 M AX 76 4- 12 TEMPERATURE (°C) LX L EA KA GE C UR RE NT (n A) 1000 30 40 50 60 70 80 90 100 110 120 130 IVOUTI + (V+) = 20V MAXIMUM OUTPUT CURRENT vs. SUPPLY VOLTAGE M AX 76 4 -0 4 SUPPLY VOLTAGE (V) M AX IM UM O UT PU T CU RR EN T (m A) 3 600 4 5 6 7 8 9 10 11 12 13 14 15 16 500 400 300 200 100 0 VOUT = -5V VOUT = -12V VOUT = -15V CIRCUIT OF FIGURE 2 60 NO-LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE M AX 76 4 -0 5 SUPPLY VOLTAGE (V) NO -L OA D SU PP LY C UR RE NT (µ A) 3 65 70 75 80 85 90 100 95 4 5 6 7 8 9 10 11 12 13 14 15 16 50 -60 NO-LOAD SUPPLY CURRENT vs. TEMPERATURE 55 M AX 76 4 -0 6 TEMPERATURE (°C) NO -L OA D SU PP LY C UR RE NT (µ A) -40 -20 0 20 40 60 80 100 120 140 60 65 70 75 80 85 90 95 100 105 110 V+ = 15V V+ = 5V M A X 7 6 4 /M A X 7 6 5 /M A X 7 6 6 -5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ DC-DC Inverters _______________________________________________________________________________________ 5 1000 0.01 0 2 4 6 10 12 148 16 SUPPLY CURRENT vs. SUPPLY VOLTAGE 0.1 M AX 76 4- 17 SUPPLY VOLTAGE (V) SU PP LY C UR RE NT (m A) 1 10 100 ILOAD = 100mA ILOAD = 0mA CIRCUIT OF FIGURE 2 -60 REFERENCE OUTPUT RESISTANCE vs. TEMPERATURE M AX 76 4 -1 5 TEMPERATURE (°C) RE FE RE NC E OU TP UT R ES IS TA NC E (Ω ) -40 -20 0 20 40 60 80 100 120 140 0 50 100 150 200 250 IREF = 10µA IREF = 50µA IREF = 100µA ____________________________Typical Operating Characteristics (continued) (V+ = 5V, VOUT = -5V, TA = +25°C, unless otherwise noted.) 0.8 -60 LX ON-RESISTANCE vs. TEMPERATURE M AX 76 4 -1 3 TEMPERATURE (°C) LX O N- RE SI ST AN CE (Ω ) -40 -20 0 20 40 60 80 100 120 140 IVOUTI + (V+) = 10V 1.0 1.2 1.4 1.6 1.8 2.0 2.2 IVOUTI + (V+) = 15V IVOUTI + (V+) = 20V -60 PEAK CURRENT AT LX vs. TEMPERATURE M AX 76 4 -1 4 TEMPERATURE (°C) CU RR EN T A T LX (A ) -40 -20 0 20 40 60 80 100 120 140 0.65 0.70 0.75 0.80 0.85 0.90 0.95 IVOUTI + (V+) = 20V IVOUTI + (V+) = 15V IVOUTI + (V+) = 10V -60 REFERENCE OUTPUT vs. TEMPERATURE M AX 76 4 -1 6 TEMPERATURE (°C) RE FE RE NC E OU TP UT (V ) -40 -20 0 20 40 60 80 100 120 140 1.506 1.504 1.502 1.500 1.498 1.496 1.494 1.492 M A X 7 6 4 /M A X 7 6 5 /M A X 7 6 6 -5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ DC-DC Inverters 6 _______________________________________________________________________________________ CIRCUIT OF FIGURE 2, VOUT = -5V, ILOAD = 100mA A: VOUT, 50mV/div, AC-COUPLED B: V+, 5V TO 10V, 5V/div 5ms/div LINE-TRANSIENT RESPONSE A B 0V CIRCUIT OF FIGURE 2, V+ = 5V, VOUT = -5V, ILOAD = 140mA A: OUTPUT RIPPLE, 100mV/div B: INDUCTOR CURRENT, 500mA/div C: LX WAVEFORM, 10V/div 5µs/div DISCONTINUOUS CONDUCTION AT HALF AND FULL CURRENT LIMIT A B 0A C0V CIRCUIT OF FIGURE 2, V+ = 5V, ILOAD = 100mA, VOUT = -5V A: VOUT, 2V/div B: SHUTDOWN PULSE, 0V TO 5V, 5V/div 2ms/div TIME TO ENTER/EXIT SHUTDOWN A B 0V 0V CIRCUIT OF FIGURE 2, V+ = 5V, VOUT = -5V A: VOUT, 50mV/div, AC-COUPLED B: ILOAD, 0mA TO 100mA, 100mA/div 5ms/div LOAD-TRANSIENT RESPONSE A B 0mA ____________________________Typical Operating Characteristics (continued) (V+ = 5V, VOUT = -5V, TA = +25°C, unless otherwise noted.) M A X 7 6 4 /M A X 7 6 5 /M A X 7 6 6 -5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ DC-DC Inverters _______________________________________________________________________________________ 7 CIRCUIT OF FIGURE 2, V+ = 5V, VOUT = -5V, ILOAD = 80mA A: OUTPUT RIPPLE, 100mV/div B: INDUCTOR CURRENT, 500mA/div C: LX WAVEFORM, 10V/div 5µs/div DISCONTINUOUS CONDUCTION AT HALF CURRENT LIMIT A B 0A C0V CIRCUIT OF FIGURE 2, V+ = 5V, VOUT = -5V, ILOAD = 240mA A: OUTPUT RIPPLE, 100mV/div B: INDUCTOR CURRENT, 500mA/div C: LX WAVEFORM, 10V/div 5µs/div CONTINUOUS CONDUCTION AT FULL CURRENT LIMIT A B 0A C0V ______________________________________________________________Pin Description GroundGND5 Positive Power-Supply Input. Must be tied together. Place a 0.1µF input bypass capacitor as close to the V+ and GND pins as possible.V+6, 7 Drain of the Internal P-Channel Power MOSFET. LX has a peak current limit of 0.75A.LX8 1.5V Reference Output that can source 100µA for external loads. Bypass to ground with a 0.1µF capacitor.REF4 Active-High Shutdown Input. With SHDN high, the part is in shutdown mode and the supply current is less than 5µA. Connect to ground for normal operation. SHDN3 PIN Feedback Input. Connect FB to REF to use the internal voltage divider for a preset output. For adjustable- output operation, use an external voltage divider, as described in the section Setting the Output Voltage.FB2 Sense Input for Fixed-Output Operation (VFB = VREF). OUT must be connected to VOUT.OUT1 FUNCTIONNAME ____________________________Typical Operating Characteristics (continued) (V+ = 5V, VOUT = -5V, TA = +25°C, unless otherwise noted.) M A X 7 6 4 /M A X 7 6 5 /M A X 7 6 6 -5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ DC-DC Inverters 8 _______________________________________________________________________________________ _______________Detailed Description Operating Principle The MAX764/MAX765/MAX766 are BiCMOS, inverting, switch-mode power supplies that provide fixed outputs of -5V, -12V, and -15V, respectively; they can also be set to any desired output voltage using an external resistor divider. Their unique control scheme combines the advantages of pulse-frequency modulation (pulse skipping) and pulse-width modulation (continuous puls- ing). The internal P-channel power MOSFET allows peak currents of 0.75A, increasing the output current capability over previous pulse-frequency-modulation (PFM) devices. Figure 1 shows the MAX764/MAX765/ MAX766 block diagram. The MAX764/MAX765/MAX766 offer three main improvements over prior solutions: 1) They can operate with miniature (less than 5mm diameter) surface-mount inductors, because of their 300kHz switching frequency. 2) The current-limited PFM control scheme allows efficien- cies exceeding 80% over a wide range of load currents. 3) Maximum quiescent supply current is only 120µA. Figures 2 and 3 show the standard application circuits for these devices. In these configurations, the IC is powered from the total differential voltage between the input (V+) and output (VOUT). The principal benefit of this arrangement is that it applies the largest available signal to the gate of the internal P-channel power MOS- FET. This increased gate drive lowers switch on-resis- tance and increases DC-DC converter efficiency. Since the voltage on the LX pin swings from V+ (when the switch is ON) to IVOUTI plus a diode drop (when the MAX764 MAX765 MAX766 P TRIG Q ONE-SHOT TRIGQ ONE-SHOT S R Q CURRENT CONTROL CIRCUITS 1.5V REFERENCE N FROM OUT FROM V+ FROM V+ 0.1V (HALF CURRENT) 0.2V (FULL CURRENT) GND LX V+ OUT V+ REF SHDN ERROR COMPARATOR COMPARATOR CURRENT COMPARATOR FB Figure 1. Block Diagram switch is OFF), the range of input and output voltages is limited to a 21V absolute maximum differential voltage. When output voltages more negative than -16V are required, substitute the MAX764/MAX765/MAX766 with Maxim’s MAX774/MAX775/MAX776 or MAX1774, which use an external switch. PFM Control Scheme The MAX764/MAX765/MAX766 use a proprietary, cur- rent-limited PFM control scheme that blends the best features of PFM and PWM devices. It combines the ultra-low supply currents of traditional pulse-skipping PFM converters with the high full-load efficiencies of current-mode pulse-width modulation (PWM) convert- ers. This control scheme allows the devices to achieve high efficiencies over a wide range of loads, while the current-sense function and high operating frequency allow the use of miniature external components. As with traditional PFM converters, the internal power MOSFET is turned on when the voltage comparator senses that the output is out of regulation (Figure 1). However, unlike traditional PFM converters, switching is accomplished through the combination of a peak cur- rent limit and a pair of one-shots that set the maximum on-time (16µs) and minimum off-time (2.3µs) for the switch. Once off, the minimum off-time one-shot holds the switch off for 2.3µs. After this minimum time, the switch either 1) stays off if the output is in regulation, or 2) turns on again if the output is out of regulation. The MAX764/MAX765/MAX766 limit the peak inductor current, which allows them to run in continuous-con- duction mode and maintain high efficiency with heavy loads. (See the photo Continuous Conduction at Full Current Limit in the Typical Operating Characteristics.) This current-limiting feature is a key component of the control circuitry. Once turned on, the switch stays on until either 1) the maximum on-time one shot turns it off (16µs later), or 2) the current limit is reached. To increase light-load efficiency, the current limit is set to half the peak current limit for the first two pulses. If those pulses bring the output voltage into regulation, the volt- age comparator holds the MOSFET off and the current limit remains at half the peak current limit. If the output voltage is still out of regulation after two pulses, the cur- rent limit is raised to its 0.75A peak for the next pulse. (See the photo Discontinuous Conduction at Half and Full Current Limit in the Typical Operating Characteristics.) Shutdown Mode When SHDN is high, the MAX764/MAX765/MAX766 enter a shutdown mode in which the supply current drops to less than 5µA. In this mode, the internal biasing circuitry (including the reference) is turned off and OUT discharges to ground. SHDN is a TTL/CMOS-logic level input. Connect SHDN to GND for normal operation. With a current-limited supply, power-up the device while unloaded or in shutdown mode (hold SHDN high until V+ exceeds 3.0V) to save power and reduce power-up cur- rent surges. (See the Supply Current vs. Supply Voltage graph in the Typical Operating Characteristics.) M A X 7 6 4 /M A X 7 6 5 /M A X 7 6 6 -5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ DC-D