MAX1760HEUB+T中文资料(9)

0.8A, Low-Noise, 1MHz, Step-Up DC-DC ConverterMAX1760/MAX1760H

Table 3. Component Selection Guide

External Diode

For output voltages greater than 4V, an externalSchottky diode must be connected from LX to POUT, inparallel with the on-chip synchronous rectifier (Figure6). The diode should be rated for 0.5A. Representativedevices are Motorola MBR0520L, Nihon EP05Q03L, orgeneric 1N5817. This external diode is also recom-mended for applications that must start with input volt-ages at or below 1.8V. The Schottky diode carriescurrent during startup and after the synchronous rectifi-er turns off; thus, its current rating only needs to be500mA. Connect the diode as close to the IC as possi-ble. Do not use ordinary rectifier diodes; their slowswitching speeds and long reverse-recovery times ren-der them unacceptable. For circuits that do not requirestartup with inputs below 1.8V and have an output of 4Vor less, no external diode is needed.

time constant is:

tSS = RSSCSS

where RSS≥470k .

Placing a capacitor across the lower resistor of the cur-rent-limiting resistive divider provides both current-limitand soft-start features simultaneously (Figures 4 and 5).

Input and Output Filter Capacitors

Choose input and output filter capacitors that will ser-vice the input and output peak currents with accept-able voltage ripple. Choose input capacitors withworking voltage ratings over the maximum input volt-

Inductor Selection

The MAX1760’s high switching frequency allows theuse of a small 3.3µH surface-mount inductor. The cho-sen inductor should generally have a saturation currentrating exceeding the N-channel switch current limit;however, it is acceptable to bias the inductor currentinto saturation by as much as 20% if a slight reductionin efficiency is acceptable. Lower current-rated induc-tors may be used if ISET is employed to reduce thepeak inductor current (see the Setting theSwitchCurrent Limit and Soft-Start section). For high efficien-cy, choose an inductor with a high-frequency ferritecore material to reduce core losses. To minimize radiat-ed noise, use a toroid or shielded inductor. See Table 3for suggested components and Table 4 for a list ofcomponent suppliers. Connect the inductor from thebattery to the LX pin as close to the IC as possible.

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Figure 6. Connection with External Schottky Diode for OutputVoltages Greater than 4V, or to Assist Low-Voltage Startup

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