Datasheet
For most applications, the peak inductor current equals
the current limit. However, for applications using large
inductor values or low input voltages, the maximum
ontime limits the peak inductor current (see Inductor
Selection section).
Capacitor Selection
Choose input and output capacitors to supply the input
and output peak currents with acceptable voltage ripple.
The input filter capacitor (C
IN
) reduces peak currents
drawn from the battery and improves efficiency. Low
equivalent series resistance (ESR) capacitors are recom-
mended. Ceramic capacitors have the lowest ESR, but
low ESR tantalum or polymer capacitors offer a good bal-
ance between cost and performance.
Output voltage ripple has two components: variations in
the charge stored in the output capacitor with each LX
pulse, and the voltage drop across the capacitor’s ESR
caused by the current into and out of the capacitor:
( ) ( )
( ) ( )
( )
( )
(
)
22
RIPPLE
RIPPLE C RIPPLE ESR
PEAK
RIPPLE ESR ESR COUT
RIPPLE C
PEAK OUT
OUT BATT OUT
VV V
V I R
1L
V I -I
2 V -V C
= +
≈
≈
where I
PEAK
is the peak inductor current (see Inductor
Selection section). For ceramic capacitors, the output
voltage ripple is typically dominated by V
RIPPLE(C)
. For
example, a 10μF ceramic capacitor and a 10μH inductor
typically provide 75mV of output ripple when stepping up
from 3.3V to 5V at 50mA. Low input-to-output voltage
differences (i.e. two cells to 3.3V) require higher output
capacitor values.
Capacitance and ESR variation of temperature should be
considered for best performance in applications with wide
operating temperature ranges. Table 2 lists suggested
capacitors and suppliers.
PC Board Layout Considerations
Careful PC board layout is important for minimizing
ground bounce and noise. Keep the IC’s GND pin and the
ground leads of the input and output capacitors less than
0.2in (5mm) apart using a ground plane. In addition, keep
all connections to FB (MAX1722/MAX1723 only) and LX
as short as possible.
Table 2. Suggested Surface-Mount Capacitors and Manufacturers (C1 and C2)
MANUFACTURER
CAPACITOR
VALUE
DESCRIPTION
PHONE
WEBSITE
AVX
1µF to 10µF X7R Ceramic
843-448-9411
www.avxcorp.com
10µF to 330µF
TAJ Tantalum Series
TPS Tantalum Series
Kemet
1µF to 22µF X5R/X7R Ceramic
864-963-6300
www.kemet.com
10µF to 330µF T494 Tantalum Series
68µF to 330µF T520 Tantalum Series
Sanyo 33µF to 330µF TPC Polymer Series
408-749-9714
www.secc.co.jp
Taiyo Yuden 33µF to 330µF X5R/X7R Ceramic
800-368-2496
www.t-yuden.org
TDK 1µF to 10µF X7R Ceramic
847-803-6100
www.tdk.com
Vishay Sprague 10µF to 330µF
594D Tantalum Series
595D Tantalum Series
203-452-5664
www.vishay.com
MAX1722/MAX1723/
MAX1724
1.5μA I
Q
, Step-Up DC-DC
Converters in TSOT and µDFN
www.maximintegrated.com
Maxim Integrated
│
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