Datasheet

9
Maxim Integrated
MAX1722/MAX1723/MAX1724
1.5µA I
Q
, Step-Up DC-DC Converters in TSOT
Inductor Selection
The control scheme of the MAX1722/MAX1723/
MAX1724 permits flexibility in choosing an inductor. A
10µH inductor value performs well in most applications.
Smaller inductance values typically offer smaller physi-
cal size for a given series resistance, allowing the
smallest overall circuit dimensions. Circuits using larger
inductance values may start up at lower battery volt-
ages, provide higher efficiency, and exhibit less ripple,
but they may reduce the maximum output current. This
occurs when the inductance is sufficiently large to pre-
vent 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:
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:
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 effi-
ciency. 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):
II
V
V
OUT MAX PEAK
BATT
OUT
()
=
⎛
⎝
⎜
⎞
⎠
⎟
1
2
η
I
Vt
L
PEAK
BATT ON MAX
=
()
L
Vt
I
BATT ON MAX
LIM
<
()
MAX1724
GND
BATT
OUTPUT
V
OUT (NOM)
INPUT
0.8V TO V
OUT
10μH
C2
10μF
SHDN
LX
OUT
C1
10μF
OFF
ON
Figure 8. MAX1724 Standard Application Circuit
Table 1. Suggested Inductors and
Suppliers
MAX1722
GND
BATT
OUTPUT
2V TO 5.5
V
INPUT
0.8V TO V
OUT
10μH
LX
OUT
FB
R2
10μF
R1
10μF
Figure 7. Adjustable Output Circuit
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