MAX5025(2001) Ver la hoja de datos (PDF) - Maxim Integrated
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MAX5025 Datasheet PDF : 13 Pages
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500kHz, 36V Output, SOT23, PWM Step-Up
DC-DC Converters
For a design in which VIN = 5V, VOUT = 30V, IOUT =
4mA, η = 0.5, and TS = 2µs,
LUPPER = 87µH
and
LLOWER = 12µH.
For a worst-case scenario in which VIN = 4.75V, VOUT
= 29V, IOUT = 4.4mA, η = 0.5, and TS = 1.25µs,
LUPPER = 46µH
and
LLOWER = 9µH.
The choice of 47µH as the recommended inductance
value is reasonable given the worst-case scenario
above. In general, the higher the inductance, the lower
the switching noise. Load regulation is also better with
higher inductance.
Diode Selection
The MAX5025–MAX5028’s high switching frequency
demands a high-speed rectifier. Schottky diodes are
recommended for most applications because of their
fast recovery time and low forward-voltage drop.
Ensure that the diode’s peak current rating is greater
than or equal to the peak inductor current. Also, the
diode reverse breakdown voltage must be greater than
VOUT. Table 2 lists diode vendors.
Capacitor Selection
Output Filter Capacitor
The output filter capacitor should be 1µF or greater. To
achieve low output ripple, a capacitor with low ESR, low
ESL, and high capacitance value should be selected.
For very low output ripple applications, the output of the
boost converter can be followed by an RC filter to fur-
ther reduce the ripple. Figure 3 shows a 100Ω, 1µF fil-
ter used to reduce the switching output ripple to
1mVp-p.
X7R ceramic capacitors are better for this boost appli-
cation because of their low ESR and tighter tolerance
over temperature than the Y5V ceramic capacitors.
Table 3 below lists manufacturers of recommended
capacitors.
Input Capacitor
Bypass VCC with a 4.7µF ceramic capacitor as close to
the IC as is practical.
Applications Information
Layout Considerations
The MAX5025–MAX5028 switch at high speed, man-
dating careful attention to layout for optimum perfor-
mance. Protect sensitive analog grounds by using a
star ground configuration. Minimize ground noise by
connecting GND, PGND, the input bypass-capacitor
ground lead, and the output-filter ground lead to a sin-
gle point (star ground configuration). Also, minimize
Table 2. Schottky Diode Vendors
VENDOR
Comchip
Panasonic
ST-Microelectronics
Vishay-Telefunken
Zetex
PHONE
510-657-8671
408-942-2912
602-485-6100
402-563-6866
631-360-2222
FAX
510-657-8921
408-946-9063
602-486-6102
402-563-6296
631-360-8222
PART NUMBERS
CDBS1045
MA2Z785
TMMBAT48
BAS382
ZHCS500
Table 3. Capacitor Table
COMPANY
PHONE
Murata
814-237-1431
Taiyo Yuden
408-573-4150
TDK
847-803-6100
FAX
814-238-0490
408-573-4159
847-803-6296
PART NUMBERS
GRM42-2X7R105K050AD (1µF capacitor)
GRM32-1210R71C475R (4.7µF capacitor)
UMK325BJ105KH (1µF capacitor)
EMK316BJ475ML (4.7µF capacitor)
C3225X7R1H155K (1.5µF capacitor)
C3225X7R1H105K (1µF capacitor)
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