спасибо ... датащит посматрю тчательней ...
я уж думал я один тут сижу (
Setting the Output Voltage
The MAX8815A has a preset output voltage of 5V. To set
other output voltages, use external feedback resistors.
To set the output voltage between 3.3V and 5V, connect
FB to the center of an external resistor voltagedivider
between POUT and GND, as shown in Figure
1b. Select the value of R2 no more than 500kΩ, and
then calculate the value for R1 as follows:
R1 = R2 (VOUT/VFB - 1)
where VFB is the FB regulation voltage, 1.265V (typ).
In most step-up converter designs, a reasonable inductor
value can be derived from the following equation.
This equation sets peak-to-peak inductor current at 1/2
the DC inductor current:
L = (2 x VBATT x D x (1 - D))/(IOUT(MAX) x fSW)
where fSW is the switching frequency (2MHz), and D is
the duty factor given by D = 1 - (VBATT/VOUT). Using L
from the equation above results in a peak-to-peak
inductor current ripple of 0.5 x IOUT/(1 - D), and a peak
inductor current of 1.25 x IOUT/(1 - D). Ensure that the
peak (saturation) current rating of the inductor meets or
exceeds this requirement. The recommended inductance
range for the MAX8815A is 1μH to 2.2μH. See
Table 1 for recommended inductors.
INDUCTOR L(μH) DCR (mΩ) ISAT (A) SIZE (mm)
A1101AS-1R0M 1 45 3.3 4 x 4 x 1.2
A1101AS-2R2M 2.2 60 2.8 4 x 4 x 1.2
1072AS-1R0M 1 40 2.8 2.8 x 2.8 x 1.8
про таблицу непонял (
Output capacitor C2 in Figures 1a and 1b is required to
keep the output voltage ripple small and to ensure regulation
loop stability. The output capacitors must have
low impedance at the switching frequency. Make sure
the output capacitors maintain their capacitance over
DC bias and the desired operating temperature range.
One 22μF tantalum capacitor is recommended.
Input capacitor C1 reduces the current peaks drawn
from the battery or input power source and reduce
switching noise in the IC. The impedance of the input
capacitor at the switching frequency should be kept
very low. A ceramic capacitor is highly recommended
due to their small size and low ESR. Make sure the
input capacitors maintain their capacitance over DC
bias and the desired operating temperature range.
Ceramic capacitors with X5R or X7R dielectric temperature
characteristics generally perform well. Two 4.7μF
or one 10μF ceramic capacitors are recommended.