Rainbow Electronics MAX1672 - Manual (Page 9)

MAX1672
Step-Up/Down DC-DC Converter
in QSOP Package
_______________________________________________________________________________________ 9
Capacitor Selection
The equivalent series resistance (ESR) of both bypass
and filter capacitors affects efficiency and output rip-
ple. Output voltage ripple is the product of peak induc-
tor current and filter capacitor ESR. Use low-ESR
capacitors for best performance, or connect two or
more filter capacitors in parallel.
A 100µF, 16V, input bypass capacitor (C1) with low
ESR reduces peak battery currents and reflected noise
due to inductor current ripple. Smaller ceramic capaci-
tors may also be used for light loads or in applications
that can tolerate higher input ripple.
A 100µF, 16V, surface-mount (SMT) tantalum PS filter
capacitor (C2) with 0.1
Ω
ESR typically exhibits 20mV
output ripple (at OUT) when stepping up from 2V to 5V
at 100mA load. Smaller capacitors (down to 10µF with
higher ESR) are acceptable for light loads or in applica-
tions that can tolerate higher output ripple.
Only 4.7µF is needed at OUT (C4) to maintain linear
regulator stability. During boost operation, this capaci-
tor reduces output voltage spikes from the step-up con-
verter by forming an R-C lowpass filter along with the
P-channel MOSFET on-resistance. Output ripple can be
further reduced by increasing C4.
See Tables 4 and 5 for a list of suggested capacitors
and suppliers.
Diode Selection
The MAX1672’s high switching frequency demands a
high-speed rectifier. Schottky diodes, such as the
1N5817 or MBRS130T3, are recommended. Make sure
the diode’s current rating exceeds the maximum load
current. See Tables 4 and 5 for a list of suggested
diodes and suppliers.
Table 3. Suggested Inductor Values Table 4. Suggested Components
ILIM
INDUCTOR VALUE
(µH)
0 (5V) 0 (0.5A) 10 to 22
0 (5V) 1 (0.8A) 10
3/ 5 5
1 (3.3V) 0 (0.5A) 10
1 (3.3V) 1 (0.8A) 4.7 to 10
INDUCTORS
Sumida
CD43-100 (1.04A, 0.182
Ω
)
CD54-100 (1.44A, 0.100
Ω
)
CDRH73-100 (1.68A, 0.072 Ω )
L1
10µH
Coilcraft
DT1608C-103 (0.7A, 0.095
Ω
)
CAPACITORS
AVX
TPSE Series
Sprague
593D or 595D Series
Tantalum
DIODES
Motorola
MBRS130LT3 (1.0A, 30V)
MBR0520LT3 (0.5A, 20V)
Schottky
1N5817 Equivalent
International Rectifier
10BQ40 (1.0A, 40V)
Table 5. Component Suppliers
PHONE
AVX (803) 946-0690
Coilcraft (847) 639-6400
SUPPLIER
International
Rectifier
(310) 322-3331
Motorola (602) 303-5454
FAX
(803) 626-3123
(847) 639-1469
(310) 322-3332
(602) 994-6430
Sanyo (619) 661-6835 (619) 661-1055
Sprague (603) 224-1961 (603) 224-1430
Sumida (847) 956-0666 (847) 956-0702