comparator as shown in Figure 8. Calculate the value of

the external resistors R3 and R4 as follows:

Since the low-battery comparator is noninverting, exter-

nal hysteresis can be added by connecting a resistor

between LBO and LBI as shown in Figure 9. When LBO

is high, the series combination of R2 and R7 source

current into the LBI summing junction.

Applications Information

Inductor Selection

An inductor value of 22µH performs well in most appli-

cations. The MAX1674/MAX1675/MAX1676 will also

work with inductors in the 10µH to 47µH range. Smaller

inductance values typically offer a smaller physical size

for a given series resistance, allowing the smallest

overall circuit dimensions. However, due to higher peak

output filter capacitor ESR) also tends to be higher.

Circuits using larger inductance values exhibit higher

output current capability and larger physical dimen-

sions for a given series resistance. The inductor’s incre-

mental saturation current rating should be greater than

the peak switch-current limit, which is 1A for the

MAX1674, 500mA for the MAX1675, and 1A or 0.5A for

the MAX1676. However, it is generally acceptable to

bias the inductor into saturation by as much as 20%,

although this will slightly reduce efficiency. Table 1 lists

suggested components.

The inductor’s DC resistance significantly affects effi-

ciency. See Table 2 for a comparison of inductor speci-

fications. Calculate the maximum output current as

follows:

L = inductor value in µH

η = efficiency (typically 0.9)

I

V

V

It

VV

xL

OUT MAX

IN

OUT

LIM

OFF

OUT

IN





























–

–

2

η

High-Efficiency, Low-Supply-Current,

Compact, Step-Up DC-DC Converters

10

______________________________________________________________________________________

MAX1674

MAX1675

MAX1676

BATT

(MAX1676)

LBI

REF

GND

R3

R1

200

Ω

R4

22

µH

47

µF

0.1

µF

LX

LBO

FB

R2

100k

SHDN

OUT

CLSEL

(MAX1676)

LOW-

BATTERY

OUTPUT

0.1

µF

47

µF

Figure 8. Setting Resistor Values for the Low-Battery Indicator

MAX1674

MAX1675

MAX1676

LBI

GND

R3

R4

R7

WHERE

R2

100k

LBO

OUT

0.1

µF

47

µF

V

= 1.3V

V

= 1.3V

H

L













−

+













(

.

)

(.

) (

)

1

3

7

3

4

1

3

4

13

3

13

2

7

R

R

R

R

R

R

VV R

VR

R

OUT

Figure 9. Adding External Hysteresis to the Low-Battery

Indicator