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| ST755 ADJUSTABLE INVERTING NEGATIVE OUTPUT CURRENT MODE PWM REGULATORS s s s s s s s s 2.7V TO 11V INPUT TO ADJUSTABLE NEGATIVE OUTPUT CONVERSION 1W GUARANTEED OUTPUT POWER (VI > 4.5V, T 70C) 68% TYP. EFFICENCY AT 6V VERY LOW QUIESCENT CURRENT: 1.2mA IN ON MODE, 10A IN SHUT DOWN MODE SOFT START VERY LOW NOISE OUTPUT 160KHz FIXED FREQUENCY OSCILLATOR MIXED BIPOLAR-CMOS TECHNOLOGY DIP-8 SO-8 DESCRIPTION The ST755 is an adjustable inverting switch-mode DC-DC regulator with internal Power MOSFET that generators an adjustable negative output from a voltage input of 2.7V to 11V, output current guaranteed at 200mA (for VI > 4.5V, VO = -5V and SCHEMATIC DIAGRAM TA = 0C to 70C) and 275mA (typical value at TA = 25C, VO = -5V). A logic controlled shut down pin that interfaces directly with microprocessor reduces supply current to only 10mA. Input to Output differential voltage is limited to VI+|VO|<12.7V. No load supply current is 1.2mA. June 2003 1/10 ST755 ABSOLUTE MAXIMUM RATINGS Symbol VCC VSHDN VLX VFB ILX PTOT Top Tstg Parameter DC Input Voltage to GND (Note1) Shutdown Voltage, SS Voltage, CC Voltage Switch Voltage (LX to VCC) Feedback Voltage (VO to GND) Peak Switch Current Continuous Power Dissipation at TA = 70C (DIP-8) (SO-8) Operating Junction Temperature Range (C series) Storage Temperature Range Value -0.3 to 12 -0.3 to (VCC + 0.3) -12.5 to + 0.3 -11 to + 0.9 2 725 470 -40 to 185 -55 to +150 Unit V V V V A mW C C Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these condition is not implied. Note 1: The input to output differential voltage is limited to VCC+|VO|<12.7V THERMAL DATA Symbol Rthj-amb Parameter Thermal Resistance Junction-ambient (*) SO-8 160 DIP-8 100 Unit C/W (*) This value depends from thermal design of PCB on which the device is mounted. CONNECTION DIAGRAM (top view) PIN DESCRIPTION Pin N 1 2 3 4 5 6 7 8 Symbol SHDN VREF SS CC VO GND LX VCC Name and Function SHUT-DOWN control (VCC = ON, GND = Shutdown) Reference Output Voltage: (1.25V) Soft Start Compensation Input Negative Output Voltage Ground Switch Output Supply Voltage Input. ORDERING CODES TYPE ST755 2/10 DIP8 ST755CN SO-8 ST755CD SO-8 (T&R) ST755CD-TR ST755 ELECTRICAL CHARACTERISTICS (Refer to the test circuits, VCC = 5V, VO = -5.25 to -4.75V, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise specified. Typical value are referred at TA = 25C) Symbol VI VO IO Parameter Input Voltage Output Voltage Output Current VCC = 4.5 to 6.2V VCC = 4.5 to 6.2V VCC = 4.5 to 6.2V VCC = 4V VCC = 2.7V ISUPPLY Supply Current (Including Switching Current) Standby Current) IOFF ISC VO VO VREF VREF RDSON ILEAK ISH VIH VIL fOSC CC Short Circuit Current) Line Regulation Load Regulation Reference Voltage Reference Drift LX On Resistance LX Leakage Current) Shutdown Pin Current) SHDN Input High Threshold SHDN Input Low Threshold Oscillator Frequency Power Efficiency Compensation Pin Impedance IO =100mA 160 68 7.5 2 0.25 VDS = 10V VCC = 4 to 6.2V IO = 0 to 200mA TA = 25C TA = TMIN to TMAX 1.18 No Load No Load IO =0 to 200mA TA = 0 to 70C TA = -40 to 85C VO = -5V VO = -5V VSHDN = VCC VSHDN = 0V Test Conditions Min. 4 4.75 200 175 175 125 1.2 10 1.2 0.1 0.003 1.25 50 0.7 1 1 1.32 3.5 100 mA A A %/V %/mA V ppm/C A A V V KHz % K 5 275 Typ. Max. 11 5.25 Unit V V mA Do not overload or short the Output to Ground. If the above conditions are observed, the device may be damaged. APPLICATION INFORMATION The ST755 is an IC developed for voltage conversion from an input voltage ranging from +2.4V to 11V to a regulated adjustable negative output limited by |VO| 12.7V-VI. The circuit adopts a current-mode PWM control scheme to achieve good efficiency, high stability and low noise performance. The figure in the first page shown the detailed block diagram of the device. ST755 is realized in a BCD technology in order to achieve high temperature stability, the best REFERENCE precision, a very low quiescent current and jitter free operations. The final stage is built around a 0.7 - 2A P-Channel Power MOS. A fraction of the output current is splitted out for current detection.Internal clock frequency is fixed to 160KHz. Error amplifier drives the PWM comparator in order to keep 0V on the CC input. So R3 and R4 resistors are calculated by the following formulae R4 = (|VO|/ VREF)*R3 (see fig 1). For R3 can be choose any value between 2K and 20K. Soft-Start (SS) input is a voltage dependent-output current limit (see figure 9, Switch Current Limit vs. SS Input Voltage). SS pin is internally pulled to VREF through a 1.2 M resistor. Applying an appropriate capacitor at SS input is possible to obtain a soft-start current imitation during power up. Forcing Soft-Start (SS) input to a lower voltage through a resistive voltage driver (R1 and R2), the maximum LX current limit can be lowered according the diagram showed in figure 9. When SHDN input is low, the total current consumption is reduced to 10A. APPLICATION CIRCUIT 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, jitter free operation moreover, it ensures the full device functionality. Layout design proposed on demoboard (see picture 2) helps to lower the developing 3/10 ST755 time. Wire lengths must be minimized, filter and by-pass capacitors C1, C2 and C3 must be low ESR type, placed as close possible to the integrated circuit. The 10H inductor must be chosen built on a core, taking care that saturation current should be higher than the peak LX switch current. See the PEAK INDUCTOR CURRENT vs. LOAD CURRENT graph (figure 6). Figure 1 : TYPICAL APPLICATION CIRCUIT (*) R1 and R2 can be omitted for Iout<200mA. (**) C6: Very low noise but poor transient and load response speed. (***) C3 (alternative to C6): faster transient and load response. Figure 2 : PRINTED DEMOBOARD PIN 1 PIN 2 PIN 3 PIN 4 = VCC = VO = SHDN = GND Note: Drawings not in scale Component Values Capacitor C1 C2 C3 C4 C5 C6 4/10 Value 47 100 82 1 10 47 Unit F F pF F F pF Resistor R1 R2 R3 R4 R5 Value 130 300 10 40.7 10 Unit K K K K K ST755 TYPICAL PERFORMANCE CHARACTERISTICS (unless otherwise specified Tj = 25C Figure 3 : Load Current vs Supply Voltage Figure 6 : Peak Inductor Current vs Load Current Figure 4 : Load Current vs Supply Voltage Figure 7 : Switch ON Resistance vs Supply Voltage Figure 5 : Efficiency vs Load Current Figure 8 : Oscillator Frequency vs Temperature & Supply Voltage 5/10 ST755 Figure 9 : Switch Current Limit vs Soft Start Voltage Figure 11 : Soft Start Delay Time Figure 10 : Reference Voltage Vs Temperature 6/10 ST755 Plastic DIP-8 MECHANICAL DATA mm. DIM. MIN. A a1 B B1 b b1 D E e e3 e4 F I L Z 0.44 3.3 1.6 0.017 8.8 2.54 7.62 7.62 7.1 4.8 0.130 0.063 0.38 0.7 1.39 0.91 0.5 0.5 9.8 0.346 0.100 0.300 0.300 0.280 0.189 0.015 1.65 1.04 TYP 3.3 0.028 0.055 0.036 0.020 0.020 0.386 0.065 0.041 MAX. MIN. TYP. 0.130 MAX. inch P001F 7/10 ST755 SO-8 MECHANICAL DATA DIM. A A1 A2 B C D E e H h L k ddd 0.1 5.80 0.25 0.40 mm. MIN. 1.35 0.10 1.10 0.33 0.19 4.80 3.80 1.27 6.20 0.50 1.27 8 (max.) 0.04 0.228 0.010 0.016 TYP MAX. 1.75 0.25 1.65 0.51 0.25 5.00 4.00 MIN. 0.053 0.04 0.043 0.013 0.007 0.189 0.150 0.050 0.244 0.020 0.050 inch TYP. MAX. 0.069 0.010 0.065 0.020 0.010 0.197 0.157 0016023/C 8/10 ST755 Tape & Reel SO-8 MECHANICAL DATA mm. DIM. MIN. A C D N T Ao Bo Ko Po P 8.1 5.5 2.1 3.9 7.9 12.8 20.2 60 22.4 8.5 5.9 2.3 4.1 8.1 0.319 0.216 0.082 0.153 0.311 TYP MAX. 330 13.2 0.504 0.795 2.362 0.882 0.335 0.232 0.090 0.161 0.319 MIN. TYP. MAX. 12.992 0.519 inch 9/10 ST755 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. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. (c) The ST logo is a registered trademark of STMicroelectronics (c) 2003 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom - United States. (c) http://www.st.com 10/10 |
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