PDF ADP3605 Data sheet ( Hoja de datos )

Número de pieza	ADP3605
Descripción	120 mA Switched Capacitor Voltage Inverter with Regulated Output
Fabricantes	Analog Devices
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No Preview Available ! a 120 mA Switched Capacitor Voltage Inverter with Regulated Output ADP3605 FEATURES Fully Regulated Output Voltage (–3 V and Adjustable) High Output Current: 120 mA Output Accuracy: ؎3% 250 kHz Switching Frequency Low Shutdown Current: 2 ␮A Typical Input Voltage Range from 3 V to 6 V SO-8 and RU-14 Packages –40؇C to +85؇C Ambient Temperature Range APPLICATIONS Voltage Inverters Voltage Regulators Computer Peripherals and Add-On Cards Portable Instruments Battery Powered Devices Pagers and Radio Control Receivers Disk Drives Mobile Phones FUNCTIONAL BLOCK DIAGRAM CP+ CP– VIN S PD S1 ADP3605 SND S2 DNS S3 B DNS S4 VOUT OSC SD CLOCK GEN FEEDBACK CONTROL LOOP VSENSE GND GENERAL DESCRIPTION The ADP3605 is a 120 mA regulated output switched capacitor voltage inverter. It provides a regulated output voltage with minimum voltage loss and requires a minimum number of ex- ternal components. In addition, the ADP3605 does not require the use of an inductor. Pin-for-pin and functionally compatible with the ADP3604, the internal oscillator of the ADP3605 runs at 500 kHz nominal frequency which produces an output switching frequency of 250 kHz. This allows for the use of smaller charge pump and filter capacitors. The ADP3605 provides an accuracy of ± 3% with a typical shut- down current of 2 µA. It can also operate from a single positive input voltage as low as 3 V. The ADP3605 is offered with the regulation fixed at –3 V or adjustable via external resistors over a –3 V to –6 V range. VIN + * CIN 4.7␮F CP + 4.7␮F VIN VOUT CP+ ADP3605-3 –3.0V CO + 4.7␮F CP– OFF SD ON 0 GND VSENSE *FOR BEST PERFORMANCE, 10␮F IS RECOMMENDED CP : SPRAGUE, 293D475X0010B2W CIN, CO: TOKIN, 1E475ZY5UC205F Figure 1. Typical Application Circuit REV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 1999 1 page ADP3605 THEORY OF OPERATION The ADP3605 uses a switched capacitor principle to generate a negative voltage from a positive input voltage. An onboard oscillator generates a two phase clock to control a switching network that transfers charge between the storage capacitors. The switches turn on and off at a 250 kHz rate, which is gener- ated from an internal 500 kHz oscillator. The basic principle behind the voltage inversion scheme is illustrated in Figures 11 and 12. S1 VIN S2 + CP – S3 S4 VOUT CO Figure 11. ADP3605 Switch Configuration Charging the Pump Capacitor During phase one, S1 and S2 are ON, charging the pump ca- pacitor to the input voltage. Before the next phase begins, S1 and S2 are turned OFF as well as S3 and S4 to prevent any overlap. S3 and S4 are turned ON during the second phase (see Figure 12) and charge stored in the pump capacitor is trans- ferred to the output capacitor. S1 VIN S2 + CP – S3 S4 VOUT CO Figure 12. ADP3605 Switch Configuration Charging the Output Capacitor During the second phase, the positive terminal of the pump capacitor is connected to ground through variable resistance switch, S3, and the negative terminal is connected to the out- put, resulting in a voltage inversion at the output terminal. The ADP3605 block diagram is shown on the front page. APPLICATION INFORMATION Capacitor Selection The ADP3605’s high internal oscillator frequency permits the use of small capacitors for both the pump and the output ca- pacitors. For a given load current, factors affecting the output voltage performance are: • Pump (CP) and output (CO) capacitance. • ESR of the CP and CO. When selecting the capacitors, keep in mind that not all manu- facturers guarantee capacitor ESR in the range required by the circuit. In general, the capacitor’s ESR is inversely proportional to its physical size, so larger capacitance values and higher volt- age ratings tend to reduce ESR. Since the ESR is also a function of the operating frequency, when selecting a capacitor, make sure its value is rated at the circuit's operating frequency. Temperature is another factor affecting capacitor performance. Figure 13 illustrates the temperature effect on various capaci- tors. If the circuit has to operate at temperatures significantly different from 25°C, the capacitance and ESR values must be carefully selected to adequately compensate for the change. Various capacitor technologies offer improved performance over temperature; for example, certain tantalum capacitors provide good low-temperature ESR but at a higher cost. Table II pro- vides the ratings for different types of capacitor technologies to help the designer select the right capacitors for the applica- tion. The exact values of CIN and CO are not critical. How- ever, low ESR capacitors such as solid tantalum and multilayer ceramic capacitors are recommended to minimize voltage loss at high currents. Table III shows a partial list of the recommended low ESR capacitor manufacturers. Input Capacitor A small 1 µF input bypass capacitor, preferably with low ESR, such as tantalum or multilayer ceramic, is recommended to reduce noise and supply transients and supply part of the peak input current drawn by the ADP3605. A large capacitor is rec- ommended if the input supply is connected to the ADP3605 through long leads, or if the pulse current drawn by the device might affect other circuitry through supply coupling. Output Capacitor The output capacitor (CO) is alternately charged to the CP volt- age when CP is switched in parallel with CO. The ESR of CO introduces steps in the VOUT waveform whenever the charge pump charges CO, which contributes to VOUT ripple. Thus, ceramic or tantalum capacitors are recommended for CO to minimize ripple on the output. Figure 14 illustrates the output ripple voltage effect for various capacitance and ESR values. Note that as the capacitor value increases beyond the point where the dominant contribution to the output ripple is due to the ESR, no significant reduction in VOUT ripple is achieved by added capacitance. Since output current is supplied solely by the output capacitor, CO, during one-half of the charge-pump cycle, peak-to-peak output ripple voltage is calculated by using the following formula. VRIPPLE = 2× IL FS × CO +2× IL × ESRCO where: IL = Load Current FS = 250 kHz nominal switching frequency CO = 10 µF with an ESR of 0.15 Ω VRIPPLE = 120 mA + 2 × 120 mA × 0.15 = 60 mV 2 × 250 kHz × 10 µF Multiple smaller capacitors can be connected in parallel to yield lower ESR and lower cost. For lighter loads, proportionally smaller capacitors are required. To reduce high frequency noise, bypass the output with a 0.1 µF ceramic capacitor in parallel with the output capacitor. REV. A –5– 5 Page

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