Abstract: Impact or vibration can cause momentary interruptions when batteries lose contact. To ensure continuity of power in battery-powered systems, add this three-IC circuit. When you drop a battery-powered device, the impact can open internal contacts for as long as 10ms, producing a momentary loss of power that can cause a false low-battery indication. (There is sometimes a similar momentary effect on the device's owner, especially if the device is expensive, but that's beyond the scope of this application note). You can insure continuity of power by adding a large capacitor across the battery. The capacitor must provide a certain amount of voltage headroom as margin against the discharge of load current. The capacitor voltage varies with discharge current as dV = Idt/C, so insufficient headroom calls for an even larger capacitor. Another problem is that large capacitors tend to be leaky. Capacitor leakage is usually not a problem during normal operation, but during "sleep mode" it can be a substantial fraction of the total quiescent current and can cause a significant reduction in battery life. The circuit of Figure 1 solves all these problems. Two AA batteries provide 3V power, which is boosted to 3.3V by a stepup dc-dc converter (U3). The large reserve capacitor of 2mF or 4mF is charged from the 3.3V output via a SPST CMOS analog switch (U1). The output of this 175 switch charges the reserve capacitor and drives the input of a low-dropout linear regulator (U2). Figure 1. This circuit removes discontinuities in power by backing up the battery (two AA cells) with charge on a reserve capacitor. U2's output is set to provide 1.68V when the battery is removed. The output is also divided down by the 80k/120k divider to trip an internal comparator connected to the low-battery input (LBI). The comparator's open-drain output (LBO) feeds back to U1's digital input (DIN), which turns the switch on (high) and off (low). Figures 2-5 show the circuit performance for different values of reserve capacitor and load current. Figures 5-6 remove switch-response time by wiring the switch in the ON position. Figure 2. Figure 1 circuit with 4mF reserve capacitor and 100µA load: after removing the battery, power remains for 8.7s. Figure 3. Figure 1 circuit with 4mF reserve capacitor and 100mA load: after removing the battery, power remains for 10.8ms. Figure 4. Figure 1 circuit with 2mF reserve capacitor and 100µA load: after removing the battery, power remains for 1.48s. Figure 5. Figure 1 circuit with 2mF reserve capacitor and 100mA load: after removing the battery, power remains for 920µs. Figure 6. Figure 1 circuit with 2mF reserve capacitor, 100µA load, and switch wired closed: after removing the battery, power remains for 544ms. Figure 7. Figure 1 circuit with 2mF reserve capacitor, 100mA load, and switch wired closed: after removing the battery, power remains for 1.08ms. 의견을 보내주세요! 위 내용이 도움이 되셨나요? 여러분의 의견을 기다립니다 — Maxim은 보내주신 정정이나 제안사항을 반영하고 있습니다. 이 페이지를 평가하고 의견을 보내주십시오. 자동 업데이트 관심있는 분야의 애플리케이션 노트가 나올 때 자동으로 업데이트 받고 싶으세요? 그렇다면 EE-Mail™을 신청하십시오. 추가 정보   APP 3209: Jun 21, 2004 MAX1674 고효율, 저소비전류, 콤팩트, 스텝 업 DC-DC 컨버터 전체 데이터 시트 (PDF, 536kB) 무료 샘플 MAX4501 저전압, SPST, CMOS 아날로그 스위치 전체 데이터 시트 (PDF, 328kB) 무료 샘플 MAX882 5V/3.3V 또는 가변, 저전압강하, Low-IQ, 대기 모드를 가진 200mA 선형 레귤레이터 전체 데이터 시트 (PDF, 364kB) 무료 샘플   다운로드, PDF 형식 (136kB)  AN3209, AN 3209, APP3209, Appnote3209, Appnote 3209