IC PWR SUPPLY DDR 28-TQFN

MAX8632ETI+T

Manufacturer Part NumberMAX8632ETI+T
DescriptionIC PWR SUPPLY DDR 28-TQFN
ManufacturerMaxim Integrated Products
MAX8632ETI+T datasheet
 


Specifications of MAX8632ETI+T

ApplicationsController, DDRVoltage - Input2 ~ 28 V
Number Of Outputs1Voltage - Output1.8V, 2.5V, 0.7 ~ 5.5 V
Operating Temperature-40°C ~ 85°CMounting TypeSurface Mount
Package / Case28-TQFN Exposed PadOutput Voltage1.8 V, 2.5 V, 0.7 V to 5.5 V
Output Current15 AInput Voltage2 V to 28 V
Mounting StyleSMD/SMTMaximum Operating Temperature+ 85 C
Minimum Operating Temperature- 40 CLead Free Status / RoHS StatusLead free / RoHS Compliant
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Integrated DDR Power-Supply Solution for
Desktops, Notebooks, and Graphic Cards
network (R4 and R5) used for setting the adjustable
current limit as shown in Figure 7.
The following is a procedure for calculating the value of
R4, R5, and R6:
1) Calculate the voltage, V
ILIM(NOM)
when the output voltage is at nominal:
=
×
V
10
I
ILIM NOM
(
)
LOAD MAX
(
×
R
DS ON Q
(
)
2
2) Pick a percentage of foldback, PFB, from 15%
to 40%.
3) Calculate the voltage, V
ILIM(0V)
shorted (0V):
=
×
V
P
V
ILIM V
(
0
)
FB
ILIM NOM
4) The value for R4 can be calculated as:
2
V
-
V
ILIM V
=
R
4
µ
10
A
5) The parallel combination of R5 and R6, denoted
R56, is calculated as:
2
V
=
R
56
-
µ
10
A
REF
C
REF
MAX8632
ILIM
GND
Figure 7. Foldback Current Limit
______________________________________________________________________________________
6) Then R6 can be calculated as:
R
6
, required at ILIM
LIR
7) Then R5 is calculated as:
×
1
-
)
2
, when the output is
A low-current Schottky diode, such as the CMDSH-3
from Central Semiconductor, works well for most appli-
(
)
cations. Do not use large-power diodes, because high-
er junction capacitance can charge up the voltage at
BST to the LX voltage and this exceeds the absolute
maximum rating of 6V. The boost capacitor should be
0.1µF to 4.7µF, depending on the input and output volt-
(
0
)
ages, external components, and PC board layout. The
boost capacitance should be as large as possible to
prevent it from charging to excessive voltage, but small
enough to adequately charge during the minimum low-
side MOSFET conduction time, which happens at maxi-
mum operating duty cycle (this occurs at minimum
R
4
input voltage). In addition, ensure that the boost capac-
itor does not discharge to below the minimum gate-to-
source voltage required to keep the high-side MOSFET
fully enhanced for lowest on-resistance. This minimum
gate-to-source voltage (V
V
OUT
R5
R4
where V
high-side MOSFET, and C
value where C
R6
×
×
V
R
4
R
5
6
OUT
=
(
)
(
)
V
-
V
-
V
OUT
ILIM NOM
(
)
ILIM V
(
0
)
(
(
)
×
V
V
R
56
ILIM NOM
(
)
ILIM V
(
0
)
×
R
6
R
56
=
R
5
R
6
-
R
56
Boost-Supply Diode and
Capacitor Selection (Buck)
) is determined by:
GS(MIN)
Q
G
=
V
V
x
GS MIN
(
)
DD
C
BOOST
is 5V, Q
is the total gate charge of the
DD
G
is the boost-capacitor
BOOST
is C7 in Figure 8.
BOOST
×
R
4 -
)
23