Applications Note 34 Issue1 August 2001 ZXSC100 Power Supply for Digital Still Camera. The ZXSC100 is a DC-DC boost converter designed for single or multi-cell portable equipment. A typical application is shown in Figure 1. The application is for a digital still camera DSP power supply, providing a regulated 3.3V/250mA supply from two cell input. Other typical applications for this reference design are MP3 players and PDA’s where high efficiency step-up conversion is required. L1 D1 47uH ZHCS1000 VBATT U1 EM Vdrive BAS Isense Q1 R2 C1 FMMT617 110k 1nF C2 2V to 3V RE 100uF/80mR FB Vcc Gnd ZXSC100 R1 R3 0.033R 30k Figure 1. Digital still camera power supply solution. Materials List Ref Value Part Number Manufacture Comments U1 ZXSC100X8 Zetex DC-DC boost converter Q1 FMMT617 Zetex SuperSOT D1 ZHCS1000 Zetex 1A Schottky diode in SOT23 TM NPN transistor R1 33m⍀ Generic R2 110k Generic R3 30k Generic C1 1nF C2 100uF TPSD107M010R0080 AVX 100uF/80mohm SMT L1 47uH DO3316P-473 Coilcraft 47uF/500mohm SMT Generic AN 33 - 1 Applications Note 34 Issue1 August 2001 The ZXSC100 is an adjustable converter allowing the end user maximum flexibility in output voltage selection. The output voltage is determined by: VOUT = VFB (1+R2/R3), where VFB=730mV. The solution achieves a peak efficiency of 85%. The graphs are shown below in figures 2 and 3. Line and load regulation are also shown in figures 4 and 5 respectively. Figures 6 and 7 show waveforms of the output voltage ripple at 2V and 3V input. Figure 4. Line Regulation Figure 2. Efficiency v Input Voltage. Figure 5. Load Regulation Figure 3. Efficiency v Load Current. AN 34 - 2 Applications Note 34 Issue1 August 2001 Low Battery Detect. In many portable equipment applications a low battery flag is necessary. Two cost-effective solutions, to be used with the ZXSC100 power supply, are given below. Both solutions have been designed for low battery indication between 2.1V and 2.3V. Figure 8 shows a simple linear low battery detect circuit. This circuit would be ideal for driving an LED to indicate low power. Figure 6. Output ripple at 2V input, IOUT=250mA. Figure 8. Low Battery Detect using BC858. Figure 7. Output ripple at 3V input, IOUT=250mA. Materials List Ref Value Q2 Part Number Manufacture Comments BC858C Generic Small signal PNP transistor R4 1M Generic R5 100k Generic R6 1M Generic C3 1nF Generic AN 34 - 3 Applications Note 34 Issue1 August 2001 Low Battery Detect cont. Figure 9 shows a solution using the ZR431L configured as a comparitor. The ZR431L is an adjustable Zener shunt regulator with a 1.25V reference voltage. When the batteries voltage is above the 2.2V threshold the low battery flag is set to the reference voltage of the ZR431L, 1.25V. As the battery discharges and approaches the 2.2V threshold the low battery flag pulls up to the output voltage. This type of flag is best suited for use with a microprocessor. Another alternative to the circuits in figure 9 are supply voltage monitors such as the ZXCM series for Zetex. The ZXCM209 are reset low and the ZXCM210 are reset high. They are available in a range of threshold voltages from 4.63V to 2.63V. Figure 9 . Low Battery Detect using ZR431L. Materials List Ref Value U2 Part Number Manufacture Comments ZR431LF01 Zetex 1.25V adjustable voltage reference - 1% tol R1 100K Generic R2 130k Generic R3 1k Generic C1* 1uF Generic *Optional - used for noise suppression © Zetex plc 2001 Zetex plc Fields New Road Chadderton Oldham, OL9 8NP United Kingdom Telephone (44) 161 622 4422 Fax: (44) 161 622 4420 Zetex GmbH Streitfeldstraße 19 D-81673 München Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 Zetex Inc Suite 315 700 Veterans Memorial Highway Hauppauge NY11788 USA Telephone: (631) 360 2222 Fax: (631) 360 8222 Zetex(Asia)Ltd 3701-04 Metroplaza, Tower 1 Hing Fong Road Kwai Fong, Hong Kong China Telephone: (852) 26100 611 Fax: (852) 24250 494 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 AN 34 - 4 Applications Note 34 Issue1 August 2001 © Zetex plc 2001 Zetex plc Fields New Road Chadderton Oldham, OL9 8NP United Kingdom Telephone (44) 161 622 4422 Fax: (44) 161 622 4420 Zetex GmbH Streitfeldstraße 19 D-81673 München Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 Zetex Inc Suite 315 700 Veterans Memorial Highway Hauppauge NY11788 USA Telephone: (631) 360 2222 Fax: (631) 360 8222 Zetex(Asia)Ltd 3701-04 Metroplaza, Tower 1 Hing Fong Road Kwai Fong, Hong Kong China Telephone: (852) 26100 611 Fax: (852) 24250 494 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 AN 34 - 5