ST755 ADJUSTABLE INVERTING NEGATIVE OUTPUT CURRENT MODE PWM REGULATORS ■ ■ ■ ■ ■ ■ ■ ■ 2.7V TO 11V INPUT TO ADJUSTABLE NEGATIVE OUTPUT CONVERSION 1W GUARANTEED OUTPUT POWER (Vin>4.5V, T≤70oC) 68% TYP. EFFICENCY AT 6V VERY LOW QUIESCENT CURRENT: 1.2mA IN ON MODE 10µA IN SHUT DOWN MODE SOFT START VERY LOW NOISE OUTPUT 160KHz FIXED FREQUENCY OSCILLATOR MIXED BIPOLAR-CMOS TECHNOLOGY DESCRIPTION The ST755 is an adjustable inverting switch-mode DC-DC rergulator with internal Power MOSFET that generaters an adjustable negative output from a voltage input of 2.7V to 11V, output current guaranteed at 200mA (for DIP-8 SO-8 Vin>4.5V, Vout = -5V and 0oC ≤ Ta ≤ 70oC) and 275mA (typical value at Ta = 25 oC, Vout = -5V). A logic controlled shut down pin that interfaces directly with microprocessor reduces supply current to only 10µA. Input to Output differential voltage is limited to Vin+|Vout|<12.7V. No load supply current is 1.2mA. BLOCK DIAGRAM September 1998 1/9 ST755 ABSOLUTE MAXIMUM RATINGS Symbol Vc c SHDN Parameter Value Unit -0.3 to 12 V Shutdown Voltage -0.3 to VCC +0.3 V Other Input Voltage -0.3 to VCC +0.3 V DC Input Voltage to GND I LX Peak Switch Current 2 A Pt ot Power Dissipation (at 70 C) (for DIP-8) (for SO-8) 725 470 mW To p Operating Ambient Temperature Range -40 to 85 o C -55 to 150 o C T stg o Storage Temperature Range Absolute Maximum Rating are those values beyond which damage to the device may occur. Functional operation under these condition is not implied. CONNECTION DIAGRAM AND (top view) PIN CONNECTIONS Pin No Symbol Name and Function 1 SHDN 2 V ref SHUT-DOWN Control (VCC = On, GND=Shutdown) Reference Output Voltage (1.25V) 3 SS Soft Start 4 CC Compensation Input 5 V out Negative Output Voltage 6 G ND Ground 7 LX Switch Output 8 V CC Positive Supply-Voltage Input ORDERING NUMBERS Type ST755 2/9 DIP-8 ST755CN SO-8 (Tube) ST755CD SO-8 (T&R) ST755CD-TR ST755 ELECTRICAL CHARACTERISTICS (Refer to the test circuits, VCC = 5V, Vout = -5.25 to -4.75V, Iload = 0mA, Ta = Tmin to Tmax unless otherwise specified. Typical Value are referred at Ta = 25 oC) Symbol Parameter VI N Input Voltage Vo Output Voltage Io Output Current I SUPPLY Supply Current (Including Switching Current) I OFF Standby Current Test Conditions Io = 0 mA to 200 mA VCC = 4.5 to 6.2 V o 10 100 µA o Reference Voltage Ta = 25 C ∆V REF Reference Dritft Ta = Tmin to Tmax R DSON LX On Resistance Shutdown Input High Threshold fo Oscillator Frequency ν Power Efficency CC mA mA mA mA 175 125 VSHDN = 0V Io = 0 mA to 200 mA Shutdown Input Low Threshold V No Load, Load Regulation V il 275 -4.75 mA ∆V o V ih 200 175 V 3.5 VCC = 4 to 6.2 V Shutdown Pin Current -5 Unit 11 1.2 Line Regulation I SH -5.25 Max. No Load, VSHDN = VCC Short Circuit Current LX Leakage Current o VCC = 4.5 to 6.2 V Ta = 0 C to 70 C o o VCC = 4.5 to 6.2 V Ta = -40 C to 85 C VCC = 4 V Vout = -5 V VCC = 2.7 V Vout = -5 V I SC I LEAK Typ. 2.7 ∆V o V REF Min. 1.18 1.2 A 0.1 %/V 0.003 %/mA 1.25 1.32 VDS = 10 V ppm/ C 0.7 Ω 1 µA 1 0.25 2 Io = 100 mA Compensation Pin Impedance V o 50 µA V V 160 KHz 68 % 7.5 KΩ Do not overload or short the Output to Ground. If the above conditions are observerd, 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 |Vout| ≤ 12.7V-VIN. 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 0.7Ω - 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 = (|Vout|/Vref)*R3 (see fig 1). For R3 can be choosen any value between 2KΩ and 20KΩ. 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 MΩ resistor. Applying an appropiate capacitor at SS input is possible to obtain a soft-start current limitation during power up. Forcing Soft-Start (SS) input to a lower voltage through a resistive voltage driver (R1 and R2), the maximum LX curent limit can be lowered according the diagram showed in figure 9. When SHDN input is low, the total current consumption is reduced to 10µA. 3/9 ST755 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 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 10µH 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 Symbol Pin V CC 1 V out 2 SHDN 3 GND 4 Component Values 4/9 Capacitor Value Unit Resistor Value C1 47 µF R1 130 Unit KΩ C2 100 µF R2 300 KΩ C3 82 pF R3 10 KΩ C4 1 µF R4 40.7 KΩ C5 10 µF R5 10 KΩ C6 47 pF ST755 TYPICAL OPERATING CHARACTERISTICS Figure 3: Load Current vs Supply Voltage Figure 4: Load Current vs Supply Voltage Figure 5: Efficency vs Load Current Figure 6: Peak InductorCurrent vs Load Current Figure 7: Switch ON Resistance vs Supply Voltage Figure 8: Oscillator Frequency vs Temperature & Supply Voltage 5/9 ST755 TYPICAL OPERATING CHARACTERISTICS (continued) Figure 9: Switch Current Limit vs Soft Start Voltage Figure 11: Soft Start Delay Time 6/9 Figure 10: Reference Voltage vs temperature ST755 Plastic DIP-8 MECHANICAL DATA mm DIM. MIN. A TYP. inch MAX. MIN. 3.3 TYP. MAX. 0.130 a1 0.7 B 1.39 1.65 0.055 0.065 B1 0.91 1.04 0.036 0.041 b b1 0.028 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 0.280 I 4.8 0.189 L Z 3.3 0.44 0.130 1.6 0.017 0.063 P001F 7/9 ST755 SO-8 MECHANICAL DATA mm DIM. MIN. TYP. A a1 inch MAX. MIN. TYP. 1.75 0.1 0.068 0.25 a2 MAX. 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 0.188 0.196 E 5.8 6.2 0.228 0.244 e 1.27 0.050 e3 3.81 0.150 F 3.8 4.0 0.14 0.157 L 0.4 1.27 0.015 0.050 M S 0.6 0.023 8 (max.) 0016023 8/9 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. Specification 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. The ST logo is a trademark of STMicroelectronics 1998 STMicroelectronics – Printed in Italy – All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Mexico - Morocco - The Netherlands Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A. . 9/9