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MAX848ESE Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX848ESE Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 16 page 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters _______________________________________________________________________________________ 9 _______________Detailed Description The MAX848/MAX849 combine a switching regulator, N-channel power MOSFET, P-channel synchronous rectifier, precision reference voltage, power-good indi- cator, and battery voltage monitor, all in a single mono- lithic device. The MAX848/MAX849 are powered directly from the output. The output voltage is factory preset to 3.3V or adjustable from 2.7V to 5V with exter- nal resistors (Dual Mode™ operation). These devices start from a low 1V input voltage and remain opera- tional down to 0.7V. The MAX848/MAX849 operate with either one to three NiCd/NiMH cells or one Li-Ion cell. At power-up, an internal low-voltage oscillator drives the N-channel power switch, and the output voltage slowly builds up. The oscillator has a 25% nominal duty cycle to prevent current build-up in the inductor. An output voltage in excess of the nominal 2.25V lockout voltage activates the error comparator and internal tim- ing circuitry. The device resumes operation in either pulse-frequency-modulation (PFM) low-power mode or pulse-width-modulation (PWM) low-noise mode, select- ed by the logic control, CLK/SEL. Figure 2 shows the standard application circuit for the MAX849 configured in the high-power PWM mode. On/Off Control The MAX848/MAX849 are turned on or off by logic input pins ON1 and ON2 (Table 1). When ON1 = 1 or ON2 = 0, the part is on. When ON1 = 0 and ON2 = 1, the part is off. Both inputs have logic trip points near 0.5 x VOUT with 0.15 x VOUT hysteresis. Operating Modes The MAX848/MAX849 operate in either PFM, PWM, or PWM synchronized to an externally applied clock sig- nal. Table 2 lists each operating mode. ON REF 1.25V RDY EN START-UP OSCILLATOR Q OUT ON1 ON2 REF GND CLK/SEL FB POKIN AINSEL AIN1 AIN2 EN ADC FEEDBACK EN 300kHz OSCILLATOR 2.25V FEEDBACK AND POWER-GOOD SELECT PFM/PWM PCH 0.25 Ω NCH 0.13 Ω POUT LX PGND POK DATA MAX848/MAX849 N Q Q D EN OSC MODE PFM/PWM CONTROLLER Figure 1. Functional Diagram ON1 O ON N2 2 MAX848/MAX849 0 0 On 0 1 Off 1 0 On 1 1 On Table 1. On/Off Logic Control |
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