ZXSC100 ZETEX | Alldatasheet

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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 ZXSC100 devices are non-synchronous PFM, DC-DC controller ICs which drive an external transistor. Zetex SuperSOT4 ™ switching transistors, with saturation resistance as low as 13m Ω , are recommended as the external switching element. These bipolar transistors are the best switching devices available for this type of DC-DC conversion, enabling high efficiency conversion with input voltages down to below 1 volt. 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. For the best in space saving the ZXSC100 is offered in the MSOP8 package, however the devices are also available in SO8 packaging for applications where space saving is not so critical. 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

  • SuperSOT4™ switching transistor ZXT14N20DX:VCE(sat)45mV max @ 1A load
  • 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
  • Demonstration boards available

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
  • LED Flashlight
  • LED Backlight ZXT14N20DX L1 D1 ZHCS2000 3.3V/0.1A BAS EM RE VBATT VCC GND FB ISENSE VDRIVE ZXSC100 TYPICAL APPLICATION CIRCUIT ISSUE 1 - JANUARY 2001

ELECTRICAL CHARACTERISTICS TEST CONDITIONS (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 MSOP8 500mW SO8 780mW Operating Temperature 0 to 70 °C Storage Temperature -55 to 125 °C Junction Temperature 150 °C Symbol Parameter Conditions Min Typ Max Units I CC Quiescent current Not switching 150 200 µA IDRIVE Base drive current V RE =V CC 51 0 m A VDRIVE VDRIVE o/p voltage V RE =V CC,I DRIVE = 5mA 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 VCC(hys) Supply start up to shutdown hysteresis 80 mV IFB 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 ZXT14N20DX as pass element 1 20 V 1 Depends on breakdown voltage of pass device. See ZXT14N20DX data sheet

ELECTRICAL CHARACTERISTICS: AC PARAMETERS2 TEST CONDITIONS (Unless otherwise stated) ) VCC=1.2V, TA = 25°C Symbol Parameter Conditions Min Typ Max Units TOFF Discharge Pulse Width 1.7 3 4 µs FOSC Recommended operating frequency 3 200 kHz

2 These parameters guaranteed by Design

3 Operating frequency is application circuit dependant. See applications section ZXT14N20DX For the circuits described in the applications section, Zetex ZXT14N20DX is the recommended pass transistor. The following indicates outline data for the ZXT, more detailed information can be found in the Zetex SuperSOT4 data book or 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 20 30 V I C=10mA* Collector-Emitter Saturation Voltage VCE(sat) 4.5 mV mV mV I C=0.1A, I B=10mA* IC=1A, I B=10mA* IC=4A, I B=40mA* *Measured under pulsed conditions. Pulse width=300µs. Duty cycle ≤2% ZHCS2000 For the circuits described in the applications section Zetex ZHCS2000 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 V F 385 500 mV mV IF=1A IF=2A Reverse Current I R 300 µA VR=30V Reverse Recovery Time trr 5.5 ns Switched from I F = 500mA to IR = 500mA. Measured at IR=50mA *Measured under pulsed conditions. Pulse width=300µs. Duty cycle ≤ 2%

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. 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 applications 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 7G ND Ground 8V DRIVE Drive output for external switching transistor. Connect to base of external switching transistor. Also connect to collector of external drive transistor in higher power applications PIN DESCRIPTIONS RE EM BAS VDRIVE VCC ISENSE FB GND REFERENCE DESIGNS Three typical DC-DC step-up converter applications for the ZXSC100 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’si n a flashlight application. Low Power Solution (330mW) Efficiency

Low power solution, VOUT=3.3V, PL=0.33W ZXT14N20DX L1 D1 ZHCS2000 3.3V/0.1A BAS EM RE VBATT VCC GND FB ISENSE VDRIVE ZXSC100 Materials list Ref Value Part Number Manufacturer Comments U1 N/A ZXSC100X8 Zetex Plc Single cell converter, MSOP8 Q1 20V, 13m Ω ,7 A ZXT14N20DX Zetex Plc Low VCE(sat) NPN, MSOP8 D1 0.5V, 2A ZHCS2000 Zetex Plc 2A Shottky diode R1 0Ω * Generic Various 0805 Size R2 33m Ω Generic Various 0805 Size R3 110k Ω Generic Various 0805 Size R4 30k Ω 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.

Higher power solution, VOUT=3.3V, PL=1W ZXT14N20DX L1 D1 ZHCS2000 3.3V/0.33A BAS EM RE ZXSC100 VBATT VCC GND FB ISENSE VDRIVE Materials list Ref Value Part Number Manufacturer Comments U1 N/A ZXSC100X8 Zetex Plc Single cell converter, MSOP8 Q1 20V, 13m Ω ,7 A ZXT14N20DX Zetex Plc Low VCE(SAT) NPN, MSOP8 Q2 N/A 2N2907 Various Small signal transistor D1 0.5V, 2A ZHCS2000 Zetex Plc 2A Shottky diode R1 3.3 Ω * Generic Various 0805 Size R2 33m Ω Generic Various 0805 Size R3 110k Ω Generic Various 0805 Size R4 30k Ω 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.

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. ZXT13N15 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 TQ1 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. The Zetex ZXT14N20DX is an ideal choice of transistor, having the lowest saturation voltage in its class. A data sheet for the ZXT14N20DX 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. ZXT14N20DX Saturation Characteristic. 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 ZHCS2000 meets these needs. A data sheet for the ZHCS2000 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. ZXT14N20DX Saturation Characteristic.

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 ZXSC100. 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. Demonstration board A demonstration board for the 0.33W solution, is available upon request. These can be obtained through your local Zetex office or through Zetex web pages. For all reference designs, Gerber files and bill of materials can be supplied. Actual Size Top Silk Bottom CopperTop Copper Drill Holes 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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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 0.65 NOM 0.0256 NOM e1 0.33 NOM 0.0128 NOM E 2.95 3.05 0.116 0.120 H 4.78 5.03 0.188 0.198 L 0.41 0.66 0.016 0.026 θ° 0° 6° 0° 6° MSOP8 DIM Millimetres 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 K0 ° 8° 0° 8° L 0.41 1.27 0.016 0.050 SO8

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Zetex plc. Fields New Road, Chadderton, Oldham, OL9-8NP, United Kingdom. Telephone: (44)161 622 4422 (Sales), (44)161 622 4444 (General Enquiries) Fax: (44)161 622 4420 Zetex GmbH Zetex Inc. Zetex (Asia) Ltd. These are supported by Streitfeldstraße 19 47 Mall Drive, Unit 4 3701-04 Metroplaza, Tower 1 agents and distributors in D-81673 München Commack NY 11725 Hing Fong Road, major countries world-wide Germany USA Kwai Fong, Hong Kong © Zetex plc 2001 Telefon: (49) 89 45 49 49 0 Telephone: (631) 543-7100 Telephone:(852) 26100 611 Fax: (49) 89 45 49 49 49 Fax: (631) 864-7630 Fax: (852) 24250 494 www.zetex.com 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.