GND (Figure 1). Choose R2 to be less than 50kΩ:
where V
REF
= 1.25V.
Inductor Selection
The MAX1733/MAX1734 are optimized to use a 10µH
inductor over the entire operating range. A 300mA
rated inductor is enough to prevent saturation for out-
put currents up to 250mA. Saturation occurs when the
inductor’s magnetic flux density reaches the maximum
level the core can support and inductance falls.
Choose a low DC-resistance inductor to improve effi-
ciency. Tables 1 and 3 list some suggested inductors
and suppliers.
Capacitor Selection
The MAX1733/MAX1734 require output voltage ripple
(approximately 30mVp-p) for stable switching behavior.
Use a 10µF to 47µF tantalum output capacitor with
about 200mΩ to 300mΩ ESR to provide stable switch-
ing while minimizing output ripple. Choose input and
output capacitors to filter inductor currents for accept-
able voltage ripple. The input capacitor reduces peak
currents and noise at the voltage source. Input capaci-
tors must meet the input ripple requirements and volt-
age rating. Use the following equation to calculate the
maximum RMS input current:
Tables 2 and 3 list some suggested capacitors and
suppliers.
Using Ceramic C
OUT
with MAX1733
The circuit of Figure 3 is designed to allow the use of
ceramic output capacitors with the MAX1733.
Feedback is derived from the LX pin instead of the out-
put to remove the effects of phase lag in the feedback
loop. Compared to the standard applications circuit,
there are three benefits: 1) availability of ceramic vs.
tantalum; 2) size of 2.2µF 0805 vs. 22µF A-case; 3) out-
put ripple less than 10mVp-p vs. greater than 30mVp-p.
Increase the output capacitance to 4.7µF to further
reduce the output ripple. Note that this circuit exhibits
load regulation equal to the series resistance of the
inductor multiplied by the load current. This small
amount of load regulation is helpful in reducing over-
shoot of the output voltage during load transients.
