MAX8632ETI+ Maxim Integrated Products, MAX8632ETI+ Datasheet - Page 23

• Manufacturer Part Number: MAX8632ETI+
• Description: IC PWR SUPPLY DDR 28-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8632ETI+

• Applications: Controller, DDR
• Voltage - Input: 2 ~ 28 V
• Number Of Outputs: 1
• Voltage - Output: 1.8V, 2.5V, 0.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TQFN Exposed Pad
• Output Voltage: 1.8 V or 2.5 V or 0.7 V to 5.5 V
• Output Current: 15 A
• Input Voltage: 2 V to 28 V
• Supply Current: 25 uA
• Switching Frequency: 600 KHz
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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
2) Pick a percentage of foldback, PFB, from 15%
3) Calculate the voltage, V
4) The value for R4 can be calculated as:
5) The parallel combination of R5 and R6, denoted
Figure 7. Foldback Current Limit
when the output voltage is at nominal:
to 40%.
shorted (0V):
R56, is calculated as:
V
ILIM NOM
(
MAX8632
V
ILIM V
Integrated DDR Power-Supply Solution for
Desktops, Notebooks, and Graphic Cards
)
(
=
R
R
______________________________________________________________________________________
0
4
56
10
)
GND
ILIM
=
×
REF
=
=
R
×
2



DS ON Q
P
V
10
I
FB
LOAD MAX
2
(
-
ILIM(0V)
ILIM(NOM)
V
10
µ
V
A
×
ILIM V
µ
C
)



REF
(
A
V
2
ILIM NOM
-
(
0
, when the output is
R
4
)
(
)
, required at ILIM
R4
R6
×



V
1
)
OUT
-
LIR
R5
2



6) Then R6 can be calculated as:
7) Then R5 is calculated as:
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-
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
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
where V
high-side MOSFET, and C
value where C
R
6
=
DD





(
(
(
V
is 5V, Q
V
V
OUT
GS MIN
ILIM NOM
BOOST
(
(
-
(
V
R
)
V
ILIM NOM
Capacitor Selection (Buck)
G
is C7 in Figure 8.
5
OUT
)
=
=
is the total gate charge of the
(
−
Boost-Supply Diode and
R
GS(MIN)
R
V
BOOST
6
DD
6
V
×
ILIM V
×
-
)
R
-
R
4
R
x
V
(
56
0
56
ILIM V
) is determined by:
×
C
is the boost-capacitor
)
BOOST
)
R
Q
(
0
5
×
G
6
)
R
)
)
56
×
)
R
4 -





23