Step-up dc-dc converters in thin sot23-5, Table 1. suggested inductors and suppliers – Rainbow Electronics MAX1724 User Manual
Page 9
MAX1722/MAX1723/MAX1724
1.5µA I
Q
, Step-Up DC-DC Converters
in Thin SOT23-5
_______________________________________________________________________________________
9
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):
I
I
V
V
OUT MAX
PEAK
BATT
OUT
(
)
=
1
2
η
I
V
t
L
PEAK
BATT ON MAX
=
(
)
L
V
t
I
BATT ON MAX
LIM
<
(
)
MAX1724
GND
BATT
OUTPUT
V
OUT (NOM)
INPUT
0.8V TO V
OUT
10
µH
C2
10
µF
SHDN
LX
OUT
C1
10
µF
OFF
ON
Figure 8. MAX1724 Standard Application Circuit
Table 1. Suggested Inductors and
Suppliers
MAX1722
GND
BATT
OUTPUT
2V TO 5.5V
INPUT
0.8V TO V
OUT
10
µH
LX
OUT
FB
R2
10
µF
R1
10
µF
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
+81 (06) 6355-5733
www.daidoo.co.jp
Toko
3DF Type
D412F Type
847-297-0070
www.toko.com