ST755 STMICROELECTRONICS | Alldatasheet
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ADJUSTABLE INVERTING NEGATIVE OUTPUT CURRENT MODE PWM REGULATORS September 1998 n 2.7V TO 11V INPUT TO ADJUSTABLE NEGATIVE OUTPUT CONVERSION n 1W GUARANTEED OUTPUT POWER (Vin>4.5V, T≤70oC) n 68% TYP. EFFICENCY AT 6V n VERY LOW QUIESCENT CURRENT: 1.2mA IN ON MODE 10µA IN SHUT DOWN MODE n SOFT START n VERY LOW NOISE OUTPUT n 160KHz FIXED FREQUENCY OSCILLATOR n 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 BLOCK DIAGRAM DIP-8 SO-8 V in>4.5V, Vout = -5V and 0oC ≤ Ta ≤ 70oC) and 275mA (typical value at Ta =2 5oC, 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 V in+|Vout|<12.7V. No load supply current is 1.2mA.
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 SHUT-DOWN Control (V CC = On, GND=Shutdown)
2V ref Reference Output Voltage (1.25V)
3 SS Soft Start
4 CC Compensation Input
out Negative Output Voltage
6 GND Ground
7 LX Switch Output
CC Positive Supply-Voltage Input ORDERING NUMBERS Type DIP-8 SO-8 (Tube) SO-8 (T&R) ST755 ST755CN ST755CD ST755CD-TR ABSOLUTE MAXIMUM RATINGS Symbol Parameter Value Unit V cc DC Input Voltage to GND -0.3 to 12 V SHDN Shutdown Voltage -0.3 to V CC +0.3 V Other Input Voltage -0.3 to V CC +0.3 V ILX Peak Switch Current 2 A Ptot Power Dissipation (at 70oC) (forDIP-8) (forSO-8) 725 470 mW Top Operating Ambient Temperature Range -40 to 85 oC Tstg Storage Temperature Range -55 to 150 oC ST755
ELECTRICAL CHARACTERISTICS (Refer to the test circuits, VCC = 5V, Vout= -5.25 to -4.75V, Iload= 0mA, Ta =T min to Tmax unless otherwise specified. Typical Value are referred at Ta =2 5oC) Symbol Parameter Test Conditions Min. Typ. Max. Unit V IN Input Voltage 2.7 11 V Vo Output Voltage I o =0m At o2 0 0m A VCC = 4.5 to 6.2 V -5.25 -5 -4.75 V Io Output Current V CC = 4.5 to 6.2 V Ta =0 oCt o7 0oC VCC = 4.5 to 6.2 V Ta = -40oCt o8 5oC VCC =4V V out=- 5V VCC = 2.7 V Vout=- 5V 200 175 275 175 125 mA mA mA mA ISUPPLY Supply Current (Including Switching Current) No Load, VSHDN =V CC 1.2 3.5 mA IOFF Standby Current No Load, V SHDN = 0V 10 100 µ A ISC Short Circuit Current 1.2 A Δ V o Line Regulation V CC = 4 to 6.2 V 0.1 %/V Δ V o Load Regulation I o = 0 mA to 200 mA 0.003 %/mA V REF Reference Voltage T a =2 5oC 1.18 1.25 1.32 V Δ V REF Reference Dritft T a =T min to Tmax 50 ppm/ oC R DSON LX On Resistance 0.7 Ω ILEAK LX Leakage Current V DS =1 0V 1 µ A ISH Shutdown Pin Current 1 µ A V il Shutdown Input Low Threshold 0.25 V V ih Shutdown Input High Threshold fo Oscillator Frequency 160 KHz ν Power Efficency I o = 100 mA 68 % CC Compensation Pin Impedance 7.5 K Ω 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 |V out| ≤ 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 R 3 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 V ref 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 (R 1 and R 2), 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. ST755
DIM. mm inch A 3.3 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 0.5 0.020 b1 0.38 0.5 0.015 0.020 D 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 3.3 0.130 Z 0.44 1.6 0.017 0.063 P001F Plastic DIP-8 MECHANICAL DATA ST755
DIM. mm inch A 1.75 0.068 a1 0.1 0.25 0.003 0.009 a2 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 0.6 0.023 S 8 (max.) 0016023 SO-8 MECHANICAL DATA ST755
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