Datasheet

MAX17501 60V, 500mA, Ultra-Small, High-Efciency,
Synchronous Step-Down DC-DC Converter
www.maximintegrated.com
Maxim Integrated │ 15
Figure 1. Setting the Output Voltage Figure 2. Adjustable EN/UVLO Network
Soft-Start Capacitor Selection
The MAX17501 implements adjustable soft-start opera-
tion to reduce inrush current. A capacitor con nected from
theSSpintoGNDprogramsthesoft-startperiod.
The soft-start time (t
SS
) is related to the capacitor con-
nected at SS (C
SS
) by the following equation:
SS SS
C 5.55 t= ×
where t
SS
is in milliseconds and C
SS
is in nanofarads. For
example, to program a 600μs soft-start time, a 3300pF
capacitorshouldbeconnectedfromtheSSpintoGND.
Ensure that (C
SEL
x V
OUT
/t
SS
) is less than 150mA,
where C
SEL
is the selected output capacitance.
Adjusting Output Voltage
TheMAX17501A/EandMAX17501B/Fhavepresetout-
putvoltagesof3.3Vand5.0V,respectively.ConnectFB/
VO directly to the positive terminal of the output capacitor
(see the Typical Applications Circuits).
The MAX17501G/H offer an adjustable output voltage
from 0.9V to 92%V
IN
. Set the output voltage with a resis-
tive voltage-divider connected from the positive terminal
of the output capacitor (V
OUT
) to GND (see Figure 1).
Connect the center node of the divider to FB/VO. To
optimizeefficiencyandoutputaccuracy,usethefollowing
proceduretochoosethevaluesofR4andR5:
For MAX17501G, select the parallel combination of R4
andR5,Rptobelessthan15kΩ.FortheMAX17501H,
selecttheparallel combination ofR4andR5, Rp tobe
lessthan30kΩ.OnceRpisselected,calculateR4as:
OUT
Rp V
R4
0.9
×
=
CalculateR5asfollows:
OUT
R4 0.9
R5
(V - 0.9)
×
=
Setting the Input Undervoltage Lockout Level
The device offers an adjustable input undervoltage-
lockout level. Set the voltage at which the device turns
on with a resistive voltage-divider connected from V
IN
toGND(seeFigure 2). Connect the center node of the
divider to EN/UVLO.
ChooseR1tobe3.3MΩ,andthencalculateR2as:
INU
R1 1.218
R2
(V -1.218)
×
=
where V
INU
is the voltage at which the device is required
to turn on. For adjustable output voltage devices, ensure
that V
INU
is higher than 0.8 x V
OUT
.
R5
R4
FB/VO
GND
V
OUT
R2
R1
EN/UVLO
GND
V
IN