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MAX1722EZK-T Datasheet(PDF) 10 Page - Maxim Integrated Products |
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MAX1722EZK-T Datasheet(HTML) 10 Page - Maxim Integrated Products |
10 / 12 page For most applications, the peak inductor current equals the current limit. However, for applications using large inductor values or low input voltages, the maximum on- time limits the peak inductor current (see Inductor Selection section). Capacitor Selection Choose input and output capacitors to supply the input and output peak currents with acceptable voltage rip- ple. The input filter capacitor (CIN) reduces peak cur- rents drawn from the battery and improves efficiency. Low equivalent series resistance (ESR) capacitors are recommended. Ceramic capacitors have the lowest ESR, but low ESR tantalum or polymer capacitors offer a good balance between cost and performance. Output voltage ripple has two components: variations in the charge stored in the output capacitor with each LX pulse, and the voltage drop across the capacitor’s ESR caused by the current into and out of the capaci- tor: where IPEAK is the peak inductor current (see Inductor Selection section). For ceramic capacitors, the output voltage ripple is typically dominated by VRIPPLE(C). For example, a 10µF ceramic capacitor and a 10µH induc- tor typically provide 75mV of output ripple when step- ping up from 3.3V to 5V at 50mA. Low input-to-output voltage differences (i.e. two cells to 3.3V) require high- er output capacitor values. Capacitance and ESR variation of temperature should be considered for best performance in applications with wide operating temperature ranges. Table 2 lists suggested capacitors and suppliers. PC Board Layout Considerations Careful PC board layout is important for minimizing ground bounce and noise. Keep the IC’s GND pin and the ground leads of the input and output capacitors less than 0.2in (5mm) apart using a ground plane. In addition, keep all connections to FB (MAX1722/MAX1723 only) and LX as short as possible. VV V V V L VV C I RIPPLE RIPPLE C RIPPLE ESR RIPPLE ESR RIPPLE C OUT BATT OUT =+ ≈ ≈ () () () ( ) () ( ) () PEAK ESR COUT PEAK OUT I R - I- 2 1 2 2 1.5µA IQ, Step-Up DC-DC Converters in Thin SOT23-5 10 ______________________________________________________________________________________ Table 2. Suggested Surface-Mount Capacitors and Manufacturers (C1 and C2) MANUFACTURER CAPACITOR VALUE DESCRIPTION PHONE WEBSITE 1 µF to 10µF X7R Ceramic AVX 10 µF to 330µF TAJ Tantalum Series TPS Tantalum Series 843-448-9411 www.avxcorp.com 1 µF to 22µF X5R/X7R Ceramic 10 µF to 330µF T494 Tantalum Series Kemet 68 µF to 330µF T520 Tantalum Series 864-963-6300 www.kemet.com Sanyo 33 µF to 330µF TPC Polymer Series 408-749-9714 www.secc.co.jp Taiyo Yuden 33 µF to 330µF X5R/X7R Ceramic 800-368-2496 www.t-yuden.org TDK 1 µF to 10µF X7R Ceramic 847-803-6100 www.tdk.com Vishay Sprague 10 µF to 330µF 594D Tantalum Series 595D Tantalum Series 203-452-5664 www.vishay.com Chip Information TRANSISTOR COUNT: 863 |
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