MAX15020EVKIT+ Maxim Integrated Products, MAX15020EVKIT+ Datasheet - Page 12

• Manufacturer Part Number: MAX15020EVKIT+
• Description: EVAL KIT FOR MAX15020
• Manufacturer: Maxim Integrated Products

Specifications of MAX15020EVKIT+

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 30V
• Current - Output: 2A
• Voltage - Input: 7.5 ~ 40V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: MAX15020
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

When the voltage at ON/OFF rises above 1.225V, the
MAX15020 turns on. Connect a resistive divider from IN
to ON/OFF to GND to set the turn-on voltage (see
Figure 2). First select the ON/OFF to the GND resistor
(R2), then calculate the resistor from IN to ON/OFF (R1)
using the following equation:
where V
turns on, V
less than 600kΩ.
If ON/OFF is connected to IN directly, the UVLO feature
monitors the supply voltage at IN and allows operation
to start when V
Connect a resistor-divider from OUT to FB to GND to
set the output voltage (see Figure 2). First calculate the
resistor (R7) from OUT to FB using the guidelines in the
Compensation Design section. Once R7 is known, cal-
culate R8 using the following equation:
where V
The output-voltage rising slew rate tracks the V
rate, given that the control loop is relatively fast com-
pared with the V
upswing slew rate is controlled by the soft-start current
charging the capacitor connected from SS to GND
according to the formula below:
when driving V
REFIN, V
slew rate.
2A, 40V Step-Down DC-DC Converter with
Dynamic Output-Voltage Programming
12
______________________________________________________________________________________
Setting the Output-Voltage Slew Rate
dV
FB
IN
OUT
dt
OUT
= REFIN and REFIN = 0 to 3.6V.
is the input voltage at which the converter
ON/OFF
will slowly rise according to the V
IN
Applications Information
=
SS
R
Setting the ON/ OFF Threshold
rises above 7.2V.
1
R
with a slow-rising voltage source at
=
7
SS
R
R
= 1.225V and R2 is chosen to be
R
+
Setting the Output Voltage
8
8
2
R
slew rate. The maximum V
=
×
8
⎡
⎢
⎣
⎡
⎢
⎢
⎣
×
V
V
V
OUT
dV
ON OFF
FB
R
dt
V
7
SS
IN
/
−
1
=
⎤
⎥
⎦
R
−
7
1
R
⎤
⎥
⎥
⎦
+
8
R
8
C
I
SS
SS
SS
REFIN
slew
SS
The output-voltage falling slew rate is limited to the dis-
charge rate of C
rent to discharge the output capacitor at this rate. The
C
the output voltage falls at a slower rate based upon
leakage and additional current drain from C
Three key inductor parameters must be specified for
operation with the MAX15020: inductance value (L),
peak inductor current (I
current (I
function of operating frequency, input-to-output voltage
differential, and the peak-to-peak inductor current
(∆I
a lower ∆I
inductor value minimizes size and cost and improves
large-signal and transient response, but reduces effi-
ciency due to higher peak currents and higher peak-to-
peak output voltage ripple for the same output
capacitor. Higher inductance increases efficiency by
reducing the ripple current. Resistive losses due to
extra wire turns can exceed the benefit gained from
lower ripple current levels especially when the induc-
tance is increased without also allowing for larger
inductor dimensions. A good compromise is to choose
∆I
Calculate the inductor using the following equation:
V
optimum for typical conditions. The switching frequen-
cy (f
between 100kHz and 500kHz when synchronized to an
external clock (see the Oscillator/Synchronization Input
(SYNC) section). The peak-to-peak inductor current,
which reflects the peak-to-peak output ripple, is worst
at the maximum input voltage. See the Output
Capacitor Selection section to verify that the worst-case
output ripple is acceptable. The inductor saturating
current (I
rent during continuous output short circuit. Select an
inductor with an I
imum peak current limit of 4.5A.
IN
SS
P-P
L
). Higher ∆I
and V
discharge current is 15µA. If there is no load, then
SW
equal to 40% of the full load current.
) is fixed at 300kHz or 500kHz and can vary
SAT
SAT
L
OUT
requires a higher inductor value. A lower
). The minimum required inductance is a
) is also important to avoid runaway cur-
L
L
are typical values so that efficiency is
SS
allows for a lower inductor value while
SAT
=
(
assuming there is enough load cur-
V
IN
specification higher than the max-
V
IN
−
PEAK
V
×
OUT
f
SW
), and inductor saturation
)
×
Inductor Selection
×
∆
V
OUT
I
L
OUT
.