MAX1700EEE 查看數據表（PDF） - Maxim Integrated

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MAX1700EEE

1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters

Maxim Integrated 

1-Cell to 3-Cell, High-Power (1A),

Low-Noise, Step-Up DC-DC Converters

270k

ON/OFF

MAX1701

ONB

OUT

ONA

µC

VDD

I/O

I/O

LX POUT

MAX1700

MAX8865/MAX8866 DUAL OR

MAX8863/MAX8864 SINGLE

LOW-DROPOUT LINEAR REGULATORS

0.1µF

270k

PA

µC

RADIO

Figure 10. Momentary Pushbutton On/Off Switch

Figure 11. Typical Phone Application

Output Diode

Use a Schottky diode, such as a 1N5817, MBR0520L, or

equivalent. The Schottky diode carries current during

start-up, and in PFM mode after the synchronous rectifier

turns off. Thus, its current rating only needs to be 500mA.

Connect the diode between LX and POUT as close to the

IC as possible. Do not use ordinary rectifier diodes since

slow switching speeds and long reverse recovery times

will compromise efficiency and load regulation.

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 with

working voltage ratings over the maximum input volt-

age, and output capacitors with working voltage ratings

higher than the output.

For full output, two 100µF, 100mΩ, low-ESR tantalum out-

put filter capacitors are recommended. For loads below

250mA, a single 100µF output capacitor will suffice. The

input filter capacitor (CIN) reduces peak currents drawn

from the input source and reduces input switching noise.

The input voltage source impedance determines the

required size of the input capacitor. When operating

directly from one or two NiCd cells placed close to the

MAX1700/MAX1701, use a 22µF, low-ESR input filter

capacitor. When operating from a power source placed

farther away, or from higher impedance batteries such as

alkaline or lithium cells, use one or two 100µF, 100mΩ,

low-ESR tantalum capacitors.

Sanyo OS-CON and Panasonic SP/CB-series ceramic

capacitors offer the lowest ESR. Low-ESR tantalum

capacitors are a good choice and generally offer a

good tradeoff between price and performance. Do not

exceed the ripple current ratings of tantalum capaci-

tors. Avoid most aluminum-electrolytic capacitors,

since their ESR is often too high.

Bypass Capacitors

Two ceramic bypass capacitors are required for proper

operation. Bypass REF with a 0.22µF capacitor to GND.

Also connect a 0.22µF ceramic capacitor from OUT to

GND. Each should be placed as close to their respec-

tive pins as possible, within 0.2in. (5mm) of the DC-DC

converter IC. See Table 4 for suggested suppliers.

__________Applications Information

Push-On/Push-Off Control

A momentary pushbutton switch can be used to turn

the MAX1700/MAX1701 on and off. In Figure 10, ONA

is pulled low and ONB is pulled high when the part is

off. When the momentary switch is pressed, ONB is

pulled low and the regulator turns on. The switch must

be pressed long enough for the microcontroller to exit

reset (200ms) and drive ONA high. A small capacitor is

added to help debounce the switch. The controller

issues a logic high to ONA, which holds the part on

regardless of the switch state. To turn the regulator off,

press the switch again, allowing the controller to read

the switch status and pull ONA low. When the switch is

released, ONB is pulled high.

Use in a Typical Wireless

Phone Application

The MAX1700/MAX1701 are ideal for use in digital

cordless and PCS phones. The power amplifier (PA) is

connected directly to the boost-converter output for

maximum voltage swing (Figure 11). Low-dropout linear

regulators are used for post-regulation to generate

14 ______________________________________________________________________________________

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