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ST755
ADJUSTABLE INVERTING NEGATIVE OUTPUT CURRENT MODE PWM REGULATORS
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2.7V TO 11V INPUT TO ADJUSTABLE NEGATIVE OUTPUT CONVERSION 1W GUARANTEED OUTPUT POWER (Vin>4.5V, T70oC) 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 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
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 10A. Input to Output differential voltage is limited to Vin+|Vout|<12.7V. No load supply current is 1.2mA.
September 1998
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ABSOLUTE MAXIMUM RATINGS
Symbol Vc c SHDN I LX Pt ot To p T stg DC Input Voltage to GND Shutdown Voltage Other Input Voltage Peak Switch Current Power Dissipation (at 70 C) (for DIP-8) (for SO-8) Operating Ambient Temperature Range Storage Temperature Range
o
Parameter
Value -0.3 to 12 -0.3 to VCC +0.3 -0.3 to VCC +0.3 2 725 470 -40 to 85 -55 to 150
Unit V V V A mW
o o
C C
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 1 2 3 4 5 6 7 8 Symbol SHDN V ref SS CC V out G ND LX V CC 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 Positive Supply-Voltage Input
ORDERING NUMBERS
Type ST755 ST755CN DIP-8 SO-8 (Tube) ST755CD SO-8 (T&R) ST755CD-TR
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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 VI N Vo Io Parameter Input Voltage Output Voltage Output Current Io = 0 mA to 200 mA VCC = 4.5 to 6.2 V 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 No Load, VSHDN = VCC No Load, VSHDN = 0V
o o
Test Conditions
Min. 2.7 -5.25 200 175
Typ. -5 275 175 125 1.2 10 1.2 0.1 0.003
Max. 11 -4.75
Unit V V mA mA mA mA
I SUPPLY Supply Current (Including Switching Current) I OFF I SC V o V o V REF V REF R DSON I LEAK I SH V il V ih fo CC Standby Current Short Circuit Current Line Regulation Load Regulation Reference Voltage Reference Dritft LX On Resistance LX Leakage Current Shutdown Pin Current Shutdown Input Low Threshold Shutdown Input High Threshold Oscillator Frequency Power Efficency Compensation Pin Impedance
3.5 100
mA A A %/V %/mA
VCC = 4 to 6.2 V Io = 0 mA to 200 mA Ta = 25 C Ta = Tmin to Tmax VDS = 10 V
o
1.18
1.25 50 0.7 1
1.32
V ppm/ C A
o
1 0.25 2 160 Io = 100 mA 68 7.5
A V V KHz % K
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 0.7 - 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 = (|Vout|/Vref)*R3 (see fig 1). For R3 can be choosen 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 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 10A.
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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 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
Symbol V CC V out SHDN GND Pin 1 2 3 4
Component Values
Capacitor C1 C2 C3 C4 C5 C6 4/9 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 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
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TYPICAL OPERATING CHARACTERISTICS (continued) Figure 9: Switch Current Limit vs Soft Start Voltage Figure 10: Reference Voltage vs temperature
Figure 11: Soft Start Delay Time
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Plastic DIP-8 MECHANICAL DATA
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 mm TYP. 3.3 0.028 0.055 0.036 0.020 0.020 0.386 0.065 0.041 MAX. MIN. inch TYP. 0.130 MAX.
P001F
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SO-8 MECHANICAL DATA
DIM. MIN. A a1 a2 a3 b b1 C c1 D E e e3 F L M S 3.8 0.4 4.8 5.8 1.27 3.81 4.0 1.27 0.6 8 (max.) 0.14 0.015 5.0 6.2 0.65 0.35 0.19 0.25 0.1 mm TYP. MAX. 1.75 0.25 1.65 0.85 0.48 0.25 0.5 45 (typ.) 0.188 0.228 0.050 0.150 0.157 0.050 0.023 0.196 0.244 0.025 0.013 0.007 0.010 0.003 MIN. inch TYP. MAX. 0.068 0.009 0.064 0.033 0.018 0.010 0.019
0016023
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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 (c) 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. .
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