SP6642EU 查看數據表（PDF） - Signal Processing Technologies

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SP6642EU

Single Alkaline Cell, High Efficiency Step-Up DC-DC Converter

Signal Processing Technologies 

0.88V to

1.65V Input

22µF

100µH

350mA

0.1µF

VBATT

LX

PFI

SP6642

VOUT

100pF*

SHDN

PFO

FB

GND

22µF

R1

VOUT=

2V to 5.2V

0.1µF

*optional compensation

R2

Figure 25. Adjustable Output Voltage Circuitry

synchronous-rectifier body diode from the input

to the output. To disable the shutdown feature,

designers can connect SHDN to V .

BATT

Adjustable Output Voltage

Driving FB to ground (logic LOW) will drive

the output voltage to the fixed-voltage operation

of +3.3V + 4%. Connecting FB to a voltage

divider between VOUT and ground will select an

adjustable output voltage between +2V and

+5.5V. Refer to Figure 25. FB regulates to

+1.23V.

Since the FB leakage current is 10nA maximum,

designers should select the feedback resistor R2

in the 100kΩ to 1MΩ range. R1 can be

determined with the following equation:

R1 = R2 x

VOUT

VREF

-1

where R3 and R4 are the feedback resistors in

Figure 25, VOUT is the output voltage, and VREF

is 1.23V.

Battery Reversal Protection

The SP6642/6643 devices will tolerate single-

cell battery reversal up to the package power-

dissipation limits noted in the ABSOLUTE

MAXIMUM RATINGS section. An internal

diode in series with an internal 5Ω resistor limits

any reverse current to less than 220mA

preventing damage to the devices. Prolonged

operation above 220mA reverse-battery current

can degrade performance of the devices.

The Inductor

It is recommended that designers implement a

100µH inductor for typical application of the

SP6642/6643 devices. Lower inductor values

down to 68µH will increase the maximum

output current. Higher inductor values up to

220µH will reduce peak inductor current and

any consequent ripple and noise. The saturation-

current rating of the inductor selected must

exceed the peak current limit synthesized by the

SP6642/6643 devices' timing algorithms. This

can be calculated with the following equation:

IPEAK =

KMAX

LMIN

where

I

PEAK

is

the

peak

current,

K

MAX

is

35V-µs,

and LMIN is the minimum inductance selected.

The maximum recommended IPEAK is 350mA.

To optimize efficiency, select an inductor with

a series resistance less than 1Ω.

Table 1 lists surface mount inductor information

for the user, including series resistance and

saturation current rating.

Rev. 10-6-00

SP6642/6643 High Efficiency Step-Up DC-DC Converter

13

© Copyright 2000 Sipex Corporation

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