Datasheet

Frequency Selection
Jumper JU3 selects the MAX15020 operating switching
frequency between 300kHz or 500kHz. See Table 3 for
switching frequency selection.
Configuring the Output Voltage (OUT)
The MAX15020 EV kit step-down regulator output volt-
age is configured to 30V by resistors R7 and R8, and
with REFIN = REFOUT. The EV kit’s output voltage
(OUT) can be reconfigured in the range of 0.8V to 36V
by replacing resistors R7 and R8. To select a new value
for resistor R8, refer to the
Compensation Design sec-
tion in the MAX15020 IC data sheet. Use the following
equation to reconfigure the output voltage to the
desired value:
where V
OUT
is the desired output voltage in volts,
V
REFIN
is the voltage supplied by REFOUT or
REFIN_EXT, and R7 is typically 10kΩ.
The MAX15020 output voltage can also be adjusted
dynamically by driving REFIN_EXT between 0 and
3.6V. To use the REFIN_EXT input, place a shunt
across pins 2-3 of jumper JU2.
Reconfiguring the MAX15020 EV kit for a new output
voltage may require replacing inductor L1 and capaci-
tors C1 and/or C6 . To select a new value for inductor
L1 and capacitors C1 and C6, refer to the
Inductor
Selection , Output Capacitor Selection, and Input
Capacitor Selection sections, respectively, in the
MAX15020 IC data sheet.
Configuring the ON/ OFF Threshold
The MAX15020 EV kit turn-on threshold is configured to
32V with resistors R1 and R2. The MAX15020 turns on
when the input voltage (V
IN
) is approximately above
32V and ON/OFF is ≥ 1.23V. The ON/OFF threshold can
be reconfigured to a desired value by appropriately
selecting resistors R1 and R2. Refer to
Setting the
ON/OFF Threshold
section in the MAX15020 IC data
sheet. To reconfigure the UVLO threshold, use the fol-
lowing equation:
where resistor R1 should be in the range of 100kΩ and
V
UVLO
is the desired UVLO threshold in volts.
Place a shunt across pins 1-2 of jumper JU1 for always-
on operation, which bypasses the on/off threshold.
Resistor R11 is utilized to prevent excessive power dis-
sipation in resistor R2 when the shunt at jumper JU1 is
installed on pins 1-2.
Synchronization Input (SYNC)
The MAX15020 EV kit circuit features a selectable
300kHz or 500kHz switching frequency. Jumper JU3
sets the internal switching frequency. The EV kit’s SYNC
PCB pad can be used to synchronize the MAX15020
with an external digital clock in the range of 300kHz to
500kHz. When SYNC is driven with an external digital
clock, the MAX15020 synchronizes to the rising edge of
the external clock.
The digital square-wave clock source must provide the
following signal qualities:
• Output voltage: Logic-low = 0 to 0.8V, logic-high =
2V to 5.5V
• Input frequency = 300kHz to 500kHz (refer to the
MAX15020 IC data sheet for more information on
the SYNC input)
• Minimum pulse width = 200ns
To use external synchronization, connect the external
square-wave clock to the SYNC and GND pads.
RR
V
UVLO
12
123
1=× −
⎡
⎣
⎢
⎤
⎦
⎥
.
R
R
V
V
OUT
REFIN
8
7
1
=
−
⎡
⎣
⎢
⎤
⎦
⎥
Evaluates: MAX15020
MAX15020 Evaluation Kit
_______________________________________________________________________________________ 3
Table 3. Jumper JU3 Frequency Selection
*Default position. When operating the MAX15020 with an exter-
nal clock signal at SYNC, place the shunt on pins 1-2. Refer to
the
Oscillator/Sychronization Input section of the MAX15020 IC
data sheet for more information.
SHUNT
LOCATION
FSEL PIN
MAX15020 SWITCHING
FREQUENCY
1-2* Connects to VREG 300kHz
2-3 Connects to GND 500kHz