ZXSC410 ZXSC420 VOLTAGE MODE BOOST CONVERTER DESCRIPTION The ZXSC410 is voltage mode boost converter in SOT23-6 package. Its excellent load and line regulation means that for the full supply range from lithium Ion cells, the output voltage will typically change by less than 1%. Using high efficiency Zetex switching transistors allow output voltages of tens of volts depending on the selected transistor. The ZXSC420 includes a battery low indicator. This operates by indicating when the converter is no longer able to maintain the regulated output voltage rather than setting a preset threshold, thereby making it suitable for various battery options and load currents. FEATURES • 1.65V to 8V supply range SOT23-6 • Typical output regulation of ±1% • Over 85% typical efficiency • Output currents up to 300mA ORDERING INFORMATION • 4.5A typical shutdown current ZXSC410 DEVICE • End of regulation output ZXSC420 APPLICATIONS • System power for battery portable products REEL SIZE TAPE WIDTH QUANTITY PER REEL ZXSC410E6TA 7” 8mm 3000 units ZXSC420E6TA 7” 8mm 3000 units • LCD bias • Local voltage conversion TYPICAL APPLICATIONS DIAGRAM L1 D1 VOUT VIN ZHCS1000 C1 Q1 FMMT617 U1 VCC R2 C2 DRIVE STDN SENSE GND VFB ZXSC410 R1 R3 DEVICE MARKING • C410 ZXSC410 • C420 ZXSC420 ISSUE 2 - May 2003 1 SEMICONDUCTORS ZXSC410 ZXSC420 ABSOLUTE MAXIMUM RATINGS VCC DRIVE EOR STDN VFB, SENSE Operating Temp. Storage Temp. Power Dissipation -0.3V to -0.3V to -0.3V to -0.3V to -0.3V to -40°C to -55°C to 450mW +10V VCC + 0.3V VCC + 0.3V The lower of (+5.0V) or (VCC + 0.3V) The lower of (+5.0V) or (VCC + 0.3V) +85°C +125°C * (ZXSC420 only) * (ZXSC410 only) ELECTRICAL CHARACTERISTICS Test Conditions VCC= 3V, T= -40°C to 85°C unless otherwise stated. Symbol Parameter Conditions Limits Min Typ Units Max Supply parameters V CC V CC Range Iq 1 Quiescent Current 1.8 I STDN Shutdown Current Eff 2 Efficiency 50mA > I OUT > 300mA Acc REF Reference tolerance 1.8V < V CC < 8V TCO REF Reference Temp Co T DRV Discharge pulse width F OSC Operating Frequency 8 V CC = 8V 220 A 4.5 85 -3.0 % 3.0 0.005 1.8V < V CC < 8V V A % %/⬚C s 1.7 200 kHz Input parameters V SENSE sense voltage I SENSE sense input current V FB =0V;V SENSE =0V 22 28 34 mV -1 -7 -15 A V FB Feedback voltage I FB 2 Feedback input current T A = 25°C 291 300 V FB =0V;V SENSE =0V -1.2 V IH Shutdown high voltage 1.5 V IL Shutdown low voltage 0 dV LN Line voltage regulation 1 309 mV -4.5 A V CC V 0.55 V 0.5 %/V Output parameters I OUT 3 Output current V IN > 2V, V OUT = V IN I DRIVE Transistor drive current V DRIVE = 0.7V 2 V DRIVE Transistor voltage drive 1.8V < V CC < 8V 0 C DRIVE Mosfet gate drive cpbty VOH EOR EOR Flag output high VOL EOR EOR Flag output low I EOR = 1mA T EOR EOR delay time T A = 25°C dI LD Load current regulation 300 mA 3.4 5 V V CC V 300 I EOR = -300nA 2.5 0 70 195 mA V CC -0.4 pF 1.15 V 250 s 0.01 %mA Note 1 2 Excluding gate/base drive current. 3 IFB is typically half of these values at 3V System not device spec, including recommended transistors. ISSUE 2 - May 2003 SEMICONDUCTORS 2 ZXSC410 ZXSC420 TYPICAL CHARACTERISTICS ISSUE 2 - May 2003 3 SEMICONDUCTORS ZXSC410 ZXSC420 DEVICE DESCRIPTION Block Diagrams Bandgap Reference All threshold voltages and internal currents are derived from a temperature compensated bandgap reference circuit with a reference voltage of 1.22V nominal. VCC STDN Bandgap Reference Shutdown Dynamic Drive Output Depending on the input signal, the output is either “LOW” or “HIGH”. In the high state a 2.5mA current source (max drive voltage = VCC-0.4V) drives the base or gate of the external transistor. In order to operate the external switching transistor at optimum efficiency, both output states are initiated with a short transient current in order to quickly discharge the base or the gate of the switching transistor. Bias Generator R1 + Comp 1 _ R2 + Comp 2 _ Switching Circuit The switching circuit consists of two comparators, Comp1 and Comp2, a gate U1, a monostable and the drive output. Normally the DRIVE output is “HIGH”; the external switching transistor is turned on. Current ramps up in the inductor, the switching transistor and external current sensing resistor. This voltage is sensed by comparator, Comp2, at input ISENSE. Once the current sense voltage across the sensing resistor exceeds 20mV, comparator Comp2 through gate U1 triggers a re-triggerable monostable and turns off the output drive stage for 2µs. The inductor discharges to the load of the application. After 2µs a new charge cycle begins, thus ramping the output voltage. When the output voltage reaches the nominal value and VFB gets an input voltage of more than 300mV, the monostable is forced “on” from Comp1 through gate U1, until the feedback voltage falls below 300mV. The above action continues to maintain regulation. U1 Monostable 2µs Dynamic Drive DRIVE R3 GND VFB SENSE Fig. 1 ZXSC410 EOR, End of Regulation Detector The EOR circuit is a retriggerable 120µs monostable, which is re-triggered by every down regulating action of comparator Comp1. As long as regulation takes place, output EOR is “HIGH“ (high impedance, 100K to VCC). Short dips of the output voltage of less than 120µs are ignored. If the output voltage falls below the nominal value for more than 120µs, output EOR goes ”LOW“. The reason for this to happen is usually a slowly progressing drop of input voltage from the discharging battery. Therefore the output voltage will also start to drop slowly. With the EOR detector, batteries can be used to the ultimate end of discharge, with enough time left for a safe shutdown. Fig. 1 ZXSC420 ISSUE 2 - May 2003 SEMICONDUCTORS 4 ZXSC410 ZXSC420 PIN DESCRIPTIONS Pin No. Name Description 1 V CC Supply voltage, 1.8V to 8V. 2 GND Ground 3 STDN/EOR Shutdown ZXSC410 / End of regulation ZXSC420 4 SENSE Inductor current sense input. Internal threshold voltage set to 28mV. Connect external sense resistor. 5 V FB Reference voltage. Internal threshold set to 300mV. Connect external resistor network to set output voltage. 6 DRIVE Drive output for external switching transistor. Connect to base or gate of external switching transistor. APPLICATIONS INFORMATION Switching transistor selection Inductor Selection The choice of switching transistor has a major impact on the converter efficiency. For optimum performance, a bipolar transistor with low VCE(SAT) and high gain is required. The VCEO of the switching transistor is also an important parameter as this sees the full output voltage when the transistor is switched off. Zetex SuperSOT™ transistors are an ideal choice for this application. The inductor value must be chosen to satisfy performance, cost and size requirements of the overall solution. Schottky diode selection A list of recommended inductors is listed in the table below: Inductor selection has a significant impact on the converter performance. For applications where efficiency is critical, an inductor with a series resistance of 500m⍀ or less should be used. As with the switching transistor, the Schottky rectifier diode has a major impact on the converter efficiency. A Schottky diode with a low forward voltage and fast recovery time should be used for this application. Part No. The diode should be selected so that the maximum forward current rating 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 ZHCS Series meet these needs. Combination devices Manufacture L I PK R DC (A) ( ) CMD4D11-100MC Sumida 10µH 0.5 0.457 CMD4D11-220MC Sumida 22µH 0.4 0.676 LPO2506OB-103 Coilcraft 10µH 1.0 0.24 ST2006103 Standex Electronics Inc 10µH 0.6 0.1 Peak current definition To minimise the external component count Zetex recommends the ZX3CDBS1M832 combination of NPN transistor and Schottky diode in a 3mm x 2mm MLP package. This device is recommended for use in space critical applications. In general, the IPK value must be chosen to ensure that the switching transistor, Q1, is in full saturation with maximum output power conditions, assuming worse-case input voltage and transistor gain under all operating temperature extremes. The IC is also capable of driving MOSFETs. Zetex recommends the ZXMNS3BM832 combination of low threshold voltage N-Channel MOSFET and Schottky diode in a 3mm x 2mm MLP package. This device is recommended for use in space critical applications. Once IPK is decided the value of RSENSE can be determined by: RSENSE = VSENSE IPK ISSUE 2 - May 2003 5 SEMICONDUCTORS ZXSC410 ZXSC420 Sense Resistor A low value sense resistor is required to set the peak current. Power in this resistor is negligible due to the low sense voltage threshold, VSENSE. Below is a table of recommended sense resistors: Manufacture Series R DC (⍀) Range Size Tolerance URL Cyntec RL1220 0.022 - 10 0805 ±5% http://www.cyntec.com IRC LR1206 0.010 - 1.0 1206 ±5% http://www.ictt.com Output power calculation Output capacitors By making the above assumptions for inductance and peak current the output power can be determined by: Output capacitors are a critical choice in the overall performance of the solution. They are required to filter the output and supply load transient currents. There are three parameters which are paramount in the selection of the output capacitors, capacitance, IRIPPLE and ESR. The capacitance value is selected to meet the load transient requirements. The capacitors IRIPPLE rating must meet or exceed the current ripple of the solution. POUT = IAV x VIN x = (Watts) where IAV = IPK (TON + T DIS) X 2 (TON + T OFF ) The ESR of the output capacitor can also affect loop stability and transient performance. The capacitors selected for the solutions, and indicated in the reference designs, are optimised to provide the best overall performance. and TON = IPK x L VIN Input capacitors and The input capacitor is chosen for its voltage and RMS current rating. The use of low ESR electrolitic or tantalum capacitors is recommended. Capacitor values for optimum performance are suggested in the reference design section IPK x L TDIS = VOUT - VIN and Also note that the ESR of the input capcitor is effectively in series with the input and hence contributes to efficiency losses in the order of IRMS2 . ESR. TOFF ≅ 1.7µs (internally set by ZXSC410) and = efficiency i.e. 100% = 1 Operating frequency can be derived by: F= 1 TON + TOFF ISSUE 2 - May 2003 SEMICONDUCTORS 6 ZXSC410 ZXSC420 Output voltage adjustment Layout issues The ZXSC410/420 are adjustable output converters allowing the end user the maximum flexibilty. For adjustable operation a potential divider network is connected as follows: Layout is critical for the circuit to function in the most efficient manner 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, RSENSE 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. VOUT RA VFB RB To optimise for best performance each of these loops kept separate from each other and interconnected with short, thick traces thus minimising parasitic inductance, capacitance and resistance. Also the RSENSE resistor should be connected, with minimum trace length, between emitter lead of Q1 and ground, again minimising stray parasitics. GND The output voltage is determined by the equation: RA VOUT = VFB 1+ RB where VFB=300mV 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 IFB(MAX)=200nA to the VFB pin. Output is adjustable from VFB to the (BR)VCEO of the switching transistor, Q1. Note: For the reference designs, RA is assigned the label R2 and RB the label R3. CONNECTION DIAGRAMS ZXSC410 ZXSC420 SOT23-6 SOT23-6 VCC GND DRIVE VFB VCC GND DRIVE VFB STDN SENSE EOR SENSE ISSUE 2 - May 2003 7 SEMICONDUCTORS ZXSC410 ZXSC420 REFERENCE DESIGNS ZXSC410 DC-DC Controller VIN=2.5V to 4.2V VOUT=5V; ILOAD=100mA Bill of Materials Ref Part Number Manufacture Comments U1 Value ZXSC410E6 Zetex DC-DC converter IC U2 ZX3CDBS1M832 Zetex Low sat NPN + 1A Schottky L1 22µH CMD4D11-220 Sumida 1mm height profile R1 100mΩ LR1206 / RL1220 IRC / Cyntec 1206 / 0805 size R2 16kΩ Generic Generic 0603 size R3 1kΩ Generic Generic 0603 size C1 22µF/6V3 GRM Series Murata 1206 size C2 22µF/6V3 GRM Series Murata 1206 size C3 1nF Generic Generic 0603 size ISSUE 2 - May 2003 SEMICONDUCTORS 8 ZXSC410 ZXSC420 Performance Graphs V=1V/DIV; T=10µS/DIV V=50mV/DIV; T=10µS/DIV Switching Waveform Output Ripple ISSUE 2 - May 2003 9 SEMICONDUCTORS ZXSC410 ZXSC420 ZXSC410 as Triple Output TFT Bias AVDD=9V/180mA VON=18V/10mA VOFF=9V/10mA ZXSC410 as Triple Output TFT Bias AVDD=9V/180mA VON=27V/10mA VOFF=9V/10mA ISSUE 2 - May 2003 SEMICONDUCTORS 10 ZXSC410 ZXSC420 Sequencing AVDD and VON By adding the circuit below to the LCD bias output (VON) of the converter a 10ms delay can be achieved between AVDD power up and VON power up. The circuit operates by a delay in turning the PMOS transistor on, which transfers to a 10ms delay between input and output of the circuit. The delay is set by the RC time constant of R1 and C1. The diode, D1, discharges the gate of the PMOS when the main system supply is turned off, guaranteeing a delay every turn on cycle. ISSUE 2 - May 2003 11 SEMICONDUCTORS ZXSC410 ZXSC420 PACKAGE OUTLINE PAD LAYOUT DETAILS e b L 2 E1 E DATUM A a e1 D C A A2 A1 CONTROLLING DIMENSIONS IN MILLIMETRES APPROX CONVERSIONS INCHES. PACKAGE DIMENSIONS Millimetres Inches DIM Millimetres Inches DIM Min Max Min Max Min Max Min Max A 0.90 1.45 0.35 0.057 E 2.60 3.00 0.102 0.118 A1 0.00 0.15 0 0.006 E1 1.50 1.75 0.059 0.069 A2 0.90 1.30 0.035 0.051 L 0.10 0.60 0.004 0.002 b 0.35 0.50 0.014 0.019 e 0.95 REF 0.037 REF C 0.09 0.20 0.0035 0.008 e1 1.90 REF 0.074 REF D 2.80 3.00 0.110 0.118 L 0° 10° 0° 10° © Zetex plc 2003 Americas Asia Pacific Zetex GmbH Streitfeldstraße 19 D-81673 München Zetex Inc 700 Veterans Memorial Hwy Hauppauge, NY 11788 Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 [email protected] USA Telephone: (1) 631 360 2222 Fax: (1) 631 360 8222 [email protected] Zetex (Asia) Ltd 3701-04 Metroplaza Tower 1 Hing Fong Road Kwai Fong Hong Kong Telephone: (852) 26100 611 Fax: (852) 24250 494 [email protected] Europe Zetex plc Fields New Road Chadderton Oldham, OL9 8NP United Kingdom Telephone (44) 161 622 4444 Fax: (44) 161 622 4446 [email protected] 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 ISSUE 2 - May 2003 SEMICONDUCTORS 12