ZXSC100 DIODES | Alldatasheet

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Technical content

DESCRIPTION

The ZXSC100 series is designed for DC-DC applications where step-up voltage conversion from very low input voltages is required. These applications mainly operate from single nickel cadmium or nickel metal hydride battery cells. The circuit can start up under full load with regulation maintained down to an input voltage of only 0.926 volts. The solution configuration ensures optimum efficiency over a wider range of load currents, several circuit configurations are possible with power dissipation up to 2W. The step up output voltage is easily programmed with external resistors, the non-synchronous architecture and SuperSOT4™ device enabling an output voltage down to the input voltage level. For best performance the ZXSC100 quiescent current is a small 150µA ensuring minimum battery drain in no load conditions. The IC and discrete combination offers the ultimate cost vs performance solution for single cell DC-DC conversion. SINGLE CELL DC-DC CONVERTER SOLUTION

FEATURES

  • Efficiency maintained over a wide range of input voltages and load currents 82% efficiency @ V BATT=1V
  • Startup under full load
  • Minimum operating input voltage VBATT=0.926V
  • Adjustable output voltage down to VBATT
  • Quiescent current typically 150µA referred to input voltage
  • MSOP8 package
  • SO8 package

APPLICATIONS

  • Cordless telephones
  • MP3 players
  • PDA
  • Pagers
  • Battery backup supplies
  • Electronic toothbrush
  • GPS receivers
  • Digital camera
  • Palmtop computers APPLICATIONS(continued)
  • Hand held instruments
  • Portable medical equipment
  • Solar powered equipment FMMT617 L1 D1 ZHCS1000 3.3V/0.1A BAS EM RE VBATT VCC GND FB ISENSE VDRIVE ZXSC100 TYPICAL APPLICATION CIRCUIT

ORDERING INFORMATION

ZXSC100X8 MSOP8 ZXSC100 7” 12mm 1,000 ZXSC100N8 SO8 ZXSC100 7” 12mm 500

ELECTRICAL CHARACTERISTICS (Unless otherwise stated) VCC=1.2V, TA = 25°C Supply voltage 0.3 to 3.5V Maximum voltage other pins 0.3 to V CC+0.3V Power dissipation (25°C) MSOP8 500mW SO8 780mW Operating temperature 0 to 70°C Storage temperature -55 to 150°C Junction temperature 150°C Symbol Parameter Conditions Min. Typ. Max. Units ICC Quiescent current Not switching 150 200 µA IDRIVE Base drive current V RE =V CC 51 0 mA VDRIVE VDRIVE o/p voltage V RE =V CC,I DRIVE =5 m A V CC - 0.17 V VFB Feedback voltage 708 730 752 mV VISENSE Output current reference voltage 12 17.5 24 mV TCVISENSE ISENSE voltage temp co. 0.4 %/°C VDREF Drive current reference voltage Measured with respect to V CC 20 30 40 mV TCVDREF VDREF temp co. 1 %/°C VCC(SRT) Startup voltage Any output load 1.01 1.06 1.1 V VCC(min) Minimum operating input voltage 0.926 0.98 1 V V CC(hys) Supply start up to shutdown hysteresis 80 mV I FB Feedback input current 100 200 nA IISENSE ISENSE input current V ISENSE = 0V 3 4 5.5 µA VO(min) Minimum output voltage VCC V VO(max) Maximum output voltage FMMT617as pass element (1) 20 V TOFF Discharge pulse width 1.7 3 4 µs (1) Depends on breakdown voltage of pass device. See FMMT617 datasheet

Symbol Parameter Conditions Min Typ Max Units FOSC Recommended operating frequency 3 200 kHz 2 These parameters guaranteed by design and characterization3 Operating frequency is application circuit dependant. See applications section FMMT617 For the circuits described in the applications section, Zetex FMMT617 is the recommended pass transistor. The following indicates outline data for the transistor, more detailed information can be found at www.zetex.com ELECTRICAL CHARACTERISTICS (at TA = 25°C unless otherwise stated) PARAMETER SYMBOL MIN. TYP. MAX. UNIT CONDITIONS Collector-emitter breakdown voltage V (BR)CEO 15 18 V I C=10mA* Collector-emitter saturation voltage V CE(sat) 8 150 100 200 mV mV mV I C=0.1A, I B=10mA* IC=1A, I B=10mA* IC=3A, I B=50mA* *Measured under pulsed conditions. Pulse width=300µs. Duty cycle ≤ 2% ZHCS1000 For the circuits described in the applications section Zetex ZHCS1000 is the recommended Schottky diode. The following indicates outline data for the ZHCS, more detailed information is available at www.zetex.com ELECTRICAL CHARACTERISTICS (at Tamb = 25°C unless otherwise stated) PARAMETER SYMBOL MIN. TYP. MAX. UNIT CONDITIONS Forward voltage VF 500 mV I F=1A Reverse current I R 100 µA VR=30V Reverse recovery time t rr 12 ns Switched from IF = 500mA to IR = 500mA. Measured at IR=50mA *Measured under pulsed conditions. Pulse width=300µs. Duty cycle ≤ 2%

1.0 1.5 2.0 2.5 100 150 200 250 300 -10 0 10 20 30 40 50 60 70 80 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0 50m 100m -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 1.0 1.5 2.0 2.5 -5.0 -2.5 0.0 2.5 5.0 Output Voltage v Temperature Quiescent Current (µA) Input Voltage (V) Line Regulation Output Voltage (%) Temperature (°C) Load Regulation Load Regulation (%) Output Current (A) Quiescent Current v Input Voltage Line Regulation (%) Input Voltage (V) TYPICAL CHARACTERISTICS

The ZXSC100 is non-synchronous PFM, DC-DC controller IC which, when combined with a high performance external transistor, enables the production of a high efficiency boost converter for use in single cell applications. A block diagram is shown for the ZXSC100 in Figure 1. A shutdown circuit turns the device on or off at V CC=1V with a hysteresis of typically 80mV. At start up, comparator Comp1 turns the driver circuit and therefore the external switching transistor on. This circuit will remain active until the feedback voltage at the pin FB rises above V REF, which is set to 730mV. An external resistive divider on the FB pin sets the output voltage level. Comparator Comp2 forces the driver circuit and the external switching transistor off, if the voltage at I SENSE exceeds 25mV. The voltage at I SENSE is taken from a current sense resistor connected in series with the emitter of the switching transistor. A monostable following the output of Comp2 extends the turn-off time of the output stage by a minimum of 2us. This ensures that there is sufficient time to discharge the inductor coil before the next on period. The AND gate between the monostable and Comp1 output ensures that the switching transistor always remains on until the I SENSE threshold is reached and that the minimum discharge period is always asserted. The pulse width is constant, the pulse frequency varies with the output load. The driver circuit supplies the external switching transistor with a defined current, which is programmed by an external resistor connected between the RE pin and V CC. The internal reference voltage for the circuit is 25mV below VCC. To maximise efficiency the external transistor is switched quickly, typically being forced off within 20ns. In higher power applications more current can be supplied to the switching transistor by using a further external component. The driver transistor in the IC can be bypassed with the addition of a discrete PNP. More information on this circuit configuration can be found in the applications section. Shutdown Drive Comp2 EM VCC ISENSE FB R2VREF VDRIVE GND RE BAS Comp1 I Figure 1 ZXSC100 Block Diagram

No. Name Description 1 EM Emitter of internal drive transistor. Connect to RE in lower power applications. Must be unconnected in higher power applications 2 BAS Not connected in lower power applications. Connect to base of external drive transistor in higher power applications 3 RE Drive current sense input. Internal threshold voltage set 25mV below V CC. Connected external sense resistor. Connect emitter of external drive transistor in higher power 4V CC Supply voltage, generally NiMH, NiCd single cell 5I SENSE Inductor current sense input. Internal threshold voltage set to 25mV. Connect external sense resistor 6 FB Feedback sense. Internal threshold set to 730mV. Connect external resistive divider to output voltage ND Ground PIN DESCRIPTIONS RE EM BAS VDRIVE VCC ISENSE FB GND REFERENCE DESIGNS Three typical DC-DC step-up converter applications for the ZXSC300 are shown. Firstly with a maximum output power of 0.33W, secondly with a maximum output power of 1.0W and finally driving white LED’s in a flashlight application. Low power solution (330mW) efficiency

Low power solution, VOUT=3.3V, PL=0.33W FMMT617 L1 D1 ZHCS1000 3.3V/0.1A BAS EM RE VBATT VCC GND FB ISENSE VDRIVE ZXSC100 Ref Value Part Number Manufacturer Comments U1 N/A ZXSC100X8 Zetex Plc Single cell converter, MSOP8 Q1 20V, 13mΩ ,7 A FMMT617 Zetex Plc Low VCE(sat) NPN, SOT23 D1 0.5V, 2A ZHCS1000 Zetex Plc 1A Shottky diode R1 0Ω* Generic Various 0805 Size R2 33mΩ Generic Various 0805 Size R3 110kΩ Generic Various 0805 Size R4 30kΩ Generic Various 0805 Size C1 220µF TPSD227M010R0100 AVX Low ESR tantalum capacitor C2 220µF TPSD227M010R0100 AVX Low ESR tantalum capacitor C3 1nF Generic Various 0805 Size L1 22µH D01608C-223 D03316P-223 Coilcraft Low profile SMT * Note: Refer to External Transistor base drive selection in the Applications Section. MATERIALS LIST

Higher power solution, VOUT=3.3V, PL=1W FMMT617 L1 D1 ZHCS1000 3.3V/0.33A BAS EM RE ZXSC100 VBATT VCC GND FB ISENSE VDRIVE Ref Value Part Number Manufacturer Comments U1 N/A ZXSC100X8 Zetex Plc Single cell converter, MSOP8 Q1 20V, 13mΩ ,7 A FMMT617 Zetex Plc Low VCE(SAT) NPN, SOT23 Q2 N/A 2N2907 Various Small signal transistor D1 0.5V, 2A ZHCS1000 Zetex Plc 1A Shottky diode R1 3.3Ω * Generic Various 0805 Size R2 33mΩ Generic Various 0805 Size R3 110kΩ Generic Various 0805 Size R4 30kΩ Generic Various 0805 Size C1 220µF TPSD227M010R0100 AVX Low ESR tantalum capacitor C2 220µF TPSD227M010R0100 AVX Low ESR tantalum capacitor C3 1nF Generic Various 0805 Size L1 22µH D01608C-223 D03316P-223 Coilcraft Low profile SMT * Note: Refer to External Transistor base drive selection in the Applications Section. MATERIALS LIST

Driving white LED’s in a flashlight application The ZXSC100 solution is ideal for LED lamp driving applications operating from a single cell. In principal conversion from 1.2V to the 3.6V, typically required by white LEDs, is necessary. Load currents in the region of 20mA to 50mA being required for a single LED element. To minimise size, weight and cost, single cell operation is an advantage. The ZXSC is well matched to single cell NiCd and NiMH characteristics. The circuit will turn on at 1.06V, to maximise the life the battery can offer, the converter does not turn off until the battery voltage falls to 0.93V. The circuit itself is very simple, a minimum number of components are used and they are all small size. The ZXSC uses the very small MSOP8 package, the pass transistor is SOT23. No capacitors are required as the circuit is stable under all conditions. The inductor recommended is a low cost miniature component. No compromise is made on efficiency however. In a standard configuration efficiency well over 80% can be achieved. With careful inductor selection efficiency over 90% is possible. The inherent flexibility of the ZXSC circuit means that parallel or series LEDs can be driven depending on application needs. A simple modification to the application circuit means that the maximum pulse current can be programmed to match the characteristics of the chosen LED load, pulse current in the range 10mA to 3A and beyond can be easily achieved. An application note (AN33) is available describing various circuits for driving white LEDs. This application note includes details of circuits that optimise battery life, maximise brightness and can be constructed for minimal cost. Contact your local Zetex office for further details. FMMT617 0.22R 100µH BAS EM RE ZXSC100 WHITE LED VBATT VCC GND FB ISENSE VDRIVE

The following section is a design guide for optimum converter performance. Switching transistor selection The choice of switching transistor has a major impact on the DC-DC converter efficiency. For optimum performance, a bipolar transistor with low V CE(SAT) and high gain is required. The majority of losses in the transistor are, ‘on-state’ and can be calculated by using the formula below: P ((I xV I x V ))xT (T T AV CE(SAT) B BE(SAT) ON ON OFF) = + where I I 2AV PK From the calculations above the impact on converter efficiency can be seen. External drive transistor selection For higher power applications an external transistor is required to provide the additional base drive current to the main switching transistor. For this, any small signal PNP transistor is sufficient. Please see reference designs for recommended part numbers. Schottky diode selection As with the switching transistor the Schottky rectifier diode has a major impact on the DC-DC converter efficiency. A Schottky diode with a low forward voltage and fast recovery time should be used for this application. The majority of losses in the diode are, ‘on-state’ and can be calculated by using the formula below: P Ix V x T (T TD1 AV F(MAX) DIS On OFF = + ) where I I 2AV PK The diode should be selected so that the maximum forward current is greater or equal to the maximum peak current in the inductor, and the maximum reverse voltage is greater or equal to the output voltage. The Zetex ZHCS1000 meets these needs. A data sheet for the ZHCS1000 is available on the Zetex web site or through your local Zetex sales office. Outline information is included in the characteristics section of this data sheet. Inductor selection

The input capacitor is chosen for its voltage and RMS current rating. The use of low ESR electrolytic or tantalum capacitors is recommended. Capacitor values for optimum performance are suggested in the reference design section. Also note that the ESR of the input capacitor is effectively in series with the input and hence contributes to efficiency losses in the order of I RMS2 x ESR. Output voltage adjustment The ZXSC100 is an adjustable converter allowing the end user the maximum flexibility in output voltage selection. For adjustable operation a potential divider network is connected as indicated in the diagram. The output voltage is determined by the equation: V OUT= VFB (1 + RA / RB), where VFB=730mV The resistor values, RA and RB, should be maximised to improve efficiency and decrease battery drain. Optimisation can be achieved by providing a minimum current of I FB(MAX)=200nA to the VBATT pin. The output is adjustable from V FB to the (BR)VCEO of the switching transistor, Q1. Note: For the reference designs, RA is assigned the label R3 and RB the label R4. External transistor base drive selection Optimisation of the external switching transistor base drive may be necessary for improved efficiency in low power applications. This can be achieved by introducing an external resistor between the supply and the RE pin of the ZXSC300. The resistor value can be determined by: R V DREF B RB RA VOUT VFB

Layout is critical for the circuit to function optimally in terms of electrical efficiency, thermal considerations and noise. For ‘step-up converters’ there are four main current loops, the input loop, power-switch loop, rectifier loop and output loop. The supply charging the input capacitor forms the input loop. The power-switch loop is defined when Q1 is ‘on’, current flows from the input through the inductor, Q1, R SENSE and to ground. When Q1 is ‘off’, the energy stored in the inductor is transferred to the output capacitor and load via D1, forming the rectifier loop. The output loop is formed by the output capacitor supplying the load when Q1 is switched back off. To optimise for best performance each of these loops should be kept separate from each other and interconnections made with short, thick traces thus minimising parasitic inductance, capacitance and resistance. Also the sense resistor R2 should be connected, with minimum trace length, between emitter lead of Q1 and ground, again minimising stray parasitics. The layout for the 0.33W solution is shown below. Top silk Drill holes Actual Size Bottom CopperTop Copper 0.33W solution demo board layout

Figure 8. Output voltage ripple for 3.3V/100mA pulse cycle, giving excellent response characteristic. measurements were taken using this technique.

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Hauppauge, NY 11788 USA Telephone: (1) 631 360 2222 Fax: (1) 631 360 8222 usa.sales@zetex.com Asia Pacific Zetex (Asia) Ltd 3701-04 Metroplaza Tower 1 Hing Fong Road, Kwai Fong Hong Kong Telephone: (852) 26100 611 Fax: (852) 24250 494 asia.sales@zetex.com Corporate Headquaters Zetex plc Fields New Road, Chadderton Oldham, OL9 8NP United Kingdom Telephone (44) 161 622 4444 Fax: (44) 161 622 4446 hq@zetex.com These offices are supported by agents and distributors in major countries world-wide. This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. The Company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. For the latest product information, log on to www.zetex.com © Zetex plc 2004 RE EM BAS VDRIVE VCC ISENSE FB GND CONNECTION DIAGRAMS H E D e X 6 A A LC 1 234 5 6 7 8 B DIM Millimeters Inches MIN MAX MIN MAX A 0.91 1.11 0.036 0.044 A1 0.10 0.20 0.004 0.008 B 0.25 0.36 0.010 0.014 C 0.13 0.18 0.005 0.007 D 2.95 3.05 0.116 0.120 e 0.65NOM 0.0256NOM e1 0.33NOM 0.0128NOM E 2.95 3.05 0.116 0.120 H 4.78 5.03 0.188 0.198 MSOP8 DIM Millimeters Inches MIN MAX MIN MAX A 4.80 4.98 0.189 0.196 B 1.27 BSC 0.05 BSC C 0.53 REF 0.02 REF D 0.36 0.46 0.014 0.018 E 3.81 3.99 0.15 0.157 F 1.35 1.75 0.05 0.07 G 0.10 0.25 0.004 0.010 J 5.80 6.20 0.23 0.24 SO8