ST778ACD

ST777/778/779 LOW VOLTAGE INPUT, 3-3.3V/5V/ADJUSTABLE OUTPUT DC-DC CONVERTER WITH SYNCHRONOUS RECTIFIER ■ ■ ■ ■ ■ ■ ■ ■ ■ 1V TO 6V INPUT GUARANTEES START-UP UNDER LOAD MAXIMUM OUTPUT CURRENT OF 300mA (778 OR 779 ADJUSTED TO 3V) LOAD FULLY DISCONNECTED IN SHUTDOWN TYPICAL EFFICIENCY OF 82% INTERNAL 1A POWER SWITCH AND SYNCHRONOUS RECTIFIER ADJUSTABLE CURRENT LIMIT ALLOWS LOW-COST INDUCTORS SUPPLY CURRENT OF 270µA (NO LOAD) SHUTDOWN SUPPLY CURRENT 20µA PACKAGE AVAILABLE: DIP-8 AND SO-8 DIP-8 c u d ) s ( ct VIN u d o r P e t e l o s b O o r P Unlike others step-up DC-DC converters the ST777/778/779’s Sinchronous Rectifier turns off in the shutdown mode, fully disconnecting the output from the source. This eliminates the current drain associated with conventional step-up converters when off or in shutdown. Supply current is 270µA under no load and only 20µA in stand by mode. DESCRIPTION The ST777/778/779 are dc-dc converters that step-up from low voltage inputs requiring only three external components, an inductor (typically 22µH) and two capacitors. The device include a Sinchronous Rectifier that eliminates the need for an external catch diode, and allows regulation even when the input is greater than the output. SCHEMATIC DIAGRAM ) s t( SO-8 e t le o s b O 22µH 100µF RLIM 1 2 IN ILIM 5 LX DELAY TIMER tOFF ACTIVE RECTIFIER OUT 6 SWITCH DRIVER VO 100µF DELAY TIMER RECTIFIER CONTROL tON PGND 4 1 : N SEL 8 VREF 7 SHDN 1.25V SHUTDOWN CONTROL AGND 3 October 2002 1/11 ST777/778/779 ABSOLUTE MAXIMUM RATINGS Symbol Parameter VCC Value Unit -0.3 to +7 V -0.3 to +7 30 sec short to IN or OUT -0.3 to +7 -0.3 to +0.3 V -0.3 to (OUT+0.3) V DC Input Voltage to GND LX Switch off Pin Voltage Switch on Pin Voltage Output, Shutdown Voltage Analog and Power Ground FB Pin Voltage OUT, SHDN AGND to PGND FB PTOT Continuous Power Dissipation (at TA = 85°C) DIP-8 Continuous Power Dissipation (at TA = 85°C) SO-8 TSTG Storage Temperature Range TOP Operating Ambient Temperature Range 550 V V mW 344 -40 to 150 °C 0 to 85 °C Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these condition is not implied. ORDERING CODES CONNECTION DIAGRAM TYPE DIP-8 SO-8 ST777 ST778 ST779 ST777ACN ST778ACN ST779ACN ST777ACD ST778ACD ST779ACD SYMBOL 1 ILIM 2 3 4 IN AGND PGND 5 6 7 LX OUT SHDN s b O o s b O - NAME AND FUNCTION Sets switch current limit input. Connect to IN for 1A current limit. A resistor from ILIM to IN sets lower peak inductor currents. Input from battery Analog ground. Not internally connected to PGND. Power ground. Must be low impedance; solder directly to ground plane or star ground. Connect to AGND, close to the device. Collector of 1A NPN power switch and emitter of Sinchronous Rectifier PNP. Voltage Output. Connect filter capacitor close to pin. Shutdown input disables power supply when low. Also disconnets load from input. Threshold is set at VIN/2. ) s ( ct u d o r P e t e l o 8 o r P e t le PIN CONNECTIONS Pin No. c u d ) s t( SEL/N.C./FB - Selection pin for 3/3.3V version (778); - Not internally connected for 5V version (777); - Feedback pin for adjustable version (779). THERMAL DATA Symbol Parameter Rthj-amb Thermal Resistance Junction-ambient 2/11 DIP-8 SO-8 Unit 100 160 °C/W ST777/778/779 ELECTRICAL CHARACTERISTICS (VIN=2.5V, CI = 22µF, CO=100µF, SHDN and ILIM connected to IN, AGND connected to PGND, TA=0 to 85°C, unless otherwise specified. Typical values are referred at TA=25°C) Symbol Parameter VSTART Start up Voltage ILOAD < 10mA, TA = 25°C (Note 1) VIN(MAX) Maximum Input Voltage (Note 1,2) Output Voltage ST777 779 (set to 5V), (Note 3) ILOAD≤ 30mA, VIN = 1.1V to 5V or ILOAD≤ 80mA, VIN = 1.8V to 5V or ILOAD≤ 130mA, VIN = 2.4V to 5V 4.8 5.0 5.2 V Output Voltage ST778 (Note 3) SEL=0V ILOAD≤ 50mA,VIN =1.1V to 3.3V or ILOAD≤ 210mA,VIN =1.8V to 3.3V or ILOAD≤ 300mA,VIN =2.4V to 3.3V 3.17 3.30 3.43 V SEL=OPEN ILOAD≤ 30mA, VIN =1.1V to 3V or ILOAD≤ 210mA, VIN =1.8V to 3V or ILOAD≤ 300mA, VIN =2.4V to 3V 2.88 3.00 3.12 V 6.5 ) s t( V 20 35 µA 15 100 nA 12 40 µA VO IIN ISHDN IIN SHDN Test Conditions Output Voltage Range ST779 No Load Supply Current Shutdown Supply Current Shutdown Input Current Min. ILOAD = 0 mA, (Switch ON) (Note 5) SHDN=0V, (Switch OFF) SHDN = 0 to VIN Efficiency ILOAD=100mA Shutdown Input Threshold VIN=1V to 6V ILIM Current Limit tONMAX Maximum Switch ON Time c u d VCESAT NPN Switch saturation Voltage o r P e t e l o VCESAT NPN Rectifier Forward Drop s b O VFB IFB ILX (t s) VIN=2.5V e t le o s b O - VIN=1.8V VIN=1V 1 V c u d 270 o r P 82 % V 1.0 A -0.3 %/°C 1.2 µs 4.5 6.5 15 0.25 ISW=600mA 0.33 ISW=1000mA 0.5 ISW=400mA 0.18 ISW=600mA 0.22 ISW=1000mA µA VIN/2 + 0.25 ISW=400mA Error Comparator Trip Point ST779, over operating input voltage (Note 6) FB Pin Bias Current ST779, VFB=1.3V Switch Off Leakage Current Rectifier Off Leakage Current Unit V 2.7 (Note 4) VIH ILIM TEMPCO Current Limit Temperature Coefficient Minimum Switch Off Time tOFFMIN Max. 6 SHDN = VIN to 5V υ Typ. V V 0.4 1.23±2% V 50 nA 0.1 0.1 µA µA Note 1: Output in regulation, VOUT = VOUT (nominal) ± 4%. Note 2: At hight VIN to VOUT differentials, the maximum load current is limited by the maximum allowable power dissipation in the package. Note 3: Start-up guaranteed under these load conditions. Note 4: Minimum value is production tested. Maximum value is guaranteed by design and is not production tested. Note 5: In the ST779 supply current depends on the resistor divider used to set the output voltage. Note 6: VOUT is set to a target value of +5V by 0.1% external feedback resistors. VOUT is measured to be 5V±2.5% to guarantee the error comparator trip point. 3/11 ST777/778/779 TYPICAL APPLICATION CIRCUIT SEL / N.C. / FB 8 1 ILIM R2 Vin 1÷6V 2 V+ L1 22µH C1 22µF ST777 ST778 ST779 3 AGND ____ R1 SHDN 7 Vout C3 Vo 6 C2 100µF 4 PGND LX 5 APPLICATIONS INFORMATION R1 and R2 must be placed only in ST779 applications to set the output voltage according to the following equation: VOUT = (1.23) [(R1+R2)/R2] and to simplify the resistor selection: R1 = R2 [(VOUT/1.23)-1] It is possible to use a wide range of values for R2 (10KΩ to 50KΩ) with no significant loss of accuracy thanks to the very low FB input current. To have 1% error, the current through R2 must be at least 100 times FB’s bias current. When large values are used for the feedback resistors (R1>50KΩ), stray output impedance at FB can incidentally add "lag" to the feedback response, destabilizing the regulator and creating a larger ripple at the output. Lead lengths and circuit board traces at the FB node should be kept short. Compensate the loop by adding a "lead" compensation capacitor (C3, 100pF to 1nF) in parallel with R1. The typical value of the L1 inductor is 22µH, enough for most applications. However, are also suitable values ranging from 10µF to 47µF with a saturation rating equal to or greater than the peak switch -current limit. ) s ( ct u d o r P e t e l o s b O 4/11 c u d ) s t( Efficiency will be reduced if the inductor works near its saturation limit, while will be maximized using an inductor with a low DC resistance, preferably under 0.2Ω. Connecting ILIM to VIN the maximum LX current limit (1A) is set. If this maximum value is not required is possible to reduce it connecting a resistor between ILIM and VIN (See Figure 16 to choose the right value). The current limit value is misured when the switch current through the inductor begins to flatten and does’nt coincide with the max short circuit current. Even if the device is designed to tolerate a short circuit without any damage, it is strictly recommended to avoid a continuos and durable short circuit of the output to GND. To achieve the best performances from switching power supply topology, particular care to layout drawing is needed, in order to minimize EMI and obtain low noise. Moreover, jitter free operation ensures the full device functionality. Wire lengths must be minimized, filter and by-pass capacitors must be low ESR type, placed as close as possible to the integrated circuit. Solder AGND and PGND pins directly to a ground plane. o s b O - e t le o r P ST777/778/779 TYPICAL CHARACTERISTICS (unless otherwise specified Tj = 25°C, CI=22µF, CO=100µF) Figure 1 : Output Voltage vs Temperature Figure 2 : Output Voltage vs Temperature Figure 4 : Efficiency vs Input Voltage c u d Figure 5 : Efficiency vs Output Current e t le ) s ( ct u d o r P e Figure 3 : Efficiency vs Temperature ) s t( o r P o s b O - Figure 6 : Efficiency vs Low Output Current t e l o s b O 5/11 ST777/778/779 Figure 7 : No Load Supply Current vs Input Voltage Figure 10 : Minimum Switch Off Time vs Temperature Figure 8 : No Load Supply Current vs Temperature Figure 11 : Maximum Switch ON Time vs Temperature c u d e t le ) s ( ct u d o r P e Figure 9 : Shutdown Input Threshold vs Input Voltage t e l o s b O 6/11 ) s t( o r P o s b O - Figure 12 : FB Pin Bias Current vs Temperature ST777/778/779 Figure 13 : Error Comparator Trip Point vs Temperature Figure 15 : Maximum Output Current vs Input Voltage Figure 14 : Maximum Output Current vs Input Voltage Figure 16 : Peak Inductor Current vs Current-Limit Resistor c u d e t le ) s ( ct ) s t( o r P o s b O - u d o r P e t e l o s b O 7/11 ST777/778/779 Figure 17 : Line Transient Figure 19 : Switching Waveform Vin Vout Vout Isw Vin=1.1V Iout=30mA Figure 18 : Load Transient Figure 20 : Switching Waveform c u d ST777/779 Vout (5V) Vout o s b O Isw Iout ) s ( ct Vin=2.5V Iout=10mA to 130mA u d o PRINTED DEMOBOARD (Not in scale) r P e t e l o s b O 8/11 e t le Vin=2.5V Iout=30mA o r P ) s t( ST777/778/779 Plastic DIP-8 MECHANICAL DATA mm. inch DIM. MIN. TYP A MAX. MIN. 3.3 TYP. MAX. 0.130 a1 0.7 0.028 B 1.39 1.65 0.055 0.065 B1 0.91 1.04 0.036 0.041 b b1 0.5 0.38 0.020 0.5 D 0.015 0.020 9.8 0.386 E 8.8 0.346 e 2.54 0.100 e3 7.62 0.300 e4 7.62 0.300 F 7.1 I 4.8 L Z 0.44 1.6 ) s ( ct ro P e let 3.3 o s b O - c u d 0.017 ) s t( 0.280 0.189 0.130 0.063 u d o r P e t e l o s b O P001F 9/11 ST777/778/779 SO-8 MECHANICAL DATA mm. DIM. MIN. TYP A inch MAX. MIN. TYP. MAX. a1 1.75 0.1 0.068 0.25 a2 0.003 0.009 1.65 0.064 a3 0.65 0.85 0.025 0.033 b 0.35 0.48 0.013 0.018 b1 0.19 0.25 0.007 0.010 C 0.25 0.5 0.010 0.019 c1 45˚ (typ.) D 4.8 5.0 0.189 E 5.8 6.2 0.228 0.244 c u d e 1.27 0.050 e3 3.81 0.150 F 3.8 4.0 0.149 L 0.4 1.27 0.015 M e t le 0.6 S 8˚ (max.) ) s ( ct ) s t( 0.196 o r P 0.157 0.050 0.023 o s b O - u d o r P e t e l o s b O 0016023 10/11 ST777/778/779 c u d e t le ) s ( ct ) s t( o r P o s b O - u d o r P e t e l o s b O Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. 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