Datasheet

Inductor Selection
The control scheme of the MAX1722/MAX1723/MAX1724
permits flexibility in choosing an inductor. A 10μH induc-
tor value performs well in most applications. Smaller
inductance values typically offer smaller physical size for
a given series resistance, allowing the smallest overall
circuit dimensions. Circuits using larger inductance val-
ues may start up at lower battery voltages, provide higher
efficiency, and exhibit less ripple, but they may reduce
the maximum output current. This occurs when the induc-
tance is sufficiently large to prevent the maximum current
limit (I
LIM
) from being reached before the maximum on-
time (t
ON(MAX)
) expires.
For maximum output current, choose the inductor value
so that the controller reaches the current-limit before the
maximum on-time is triggered:
BATT ON(MAX)
LIM
Vt
L
I
<
where the maximum on-time is typically 5μs, and the
current limit (I
LIM
) is typically 500mA (see Electrical
Characteristics table).
For larger inductor values, determine the peak inductor
current (I
PEAK
) by:
BATT ON(MAX)
PEAK
Vt
I
L
=
The inductor’s incremental saturation current rating should
be greater than the peak switching current. 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 inductors and suppliers.
Maximum Output Current
The maximum output current depends on the peak induc-
tor current, the input voltage, the output voltage, and the
overall efficiency (η):
( )
BATT
PEAK
OUT MAX
OUT
V
1
II
2V

= η


Figure 7. Adjustable Output Circuit
Figure 8. MAX1724 Standard Application Circuit
Table 1. Suggested Inductors and
Suppliers
MANUFACTURER INDUCTOR
PHONE
WEBSITE
Coilcraft
DO1608 Series
DO1606 Series
847-639-2361
www.coilcraft.com
Murata LQH4C Series
770-436-1300
www.murata.com
Sumida
CDRH4D18 Series
CR32 Series
CMD4D06 Series
847-545-6700
www.sumida.com
Sumitomo/
Daidoo Electronics
CXLD140 Series
[phone]
www.daidoo.co.jp
Toko
3DF Type
D412F Type
847-297-0070
www.toko.com
MAX1722
GND
BATT
OUTPUT
2V TO 5.5V
INPUT
0.8V TO V
OUT
10µH
LX
OUT
FB
R2
10µF
R1
10µF
MAX1724
GND
BATT
OUTPUT
V
OUT (NOM)
INPUT
0.8V TO V
OUT
10µH
C2
10µF
SHDN
LX
OUT
C1
10µF
OFF
ON
MAX1722/MAX1723/
MAX1724
1.5μA I
Q
, Step-Up DC-DC
Converters in TSOT and µDFN
www.maximintegrated.com
Maxim Integrated │ 10