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
The overshoot during a full-load to no-load transient
due to stored inductor energy can be calculated as:
I
LOAD MAX
(
=
V
SOAR
×
×
2
C
OUT
Applications Information
Dropout Performance (Buck)
The output-voltage adjustable range for continuous-
conduction operation is restricted by the nonadjustable
minimum off-time one-shot. For best dropout perfor-
mance, use the slower (200kHz) on-time setting. When
working with low input voltages, the duty-factor limit
must be calculated using worst-case values for on- and
off-times. Manufacturing tolerances and internal propa-
gation delays introduce an error to the TON K-factor.
This error is greater at higher frequencies (see Table
1). Also, keep in mind that transient-response perfor-
mance of buck regulators operated too close to
dropout is poor, and bulk output capacitance must
often be added (see the V
equation in the Design
SAG
Procedure section).
The absolute point of dropout is when the inductor cur-
rent ramps down during the minimum off-time (∆I
as much as it ramps up during the on-time (∆I
ratio h = ∆I
/ ∆I
indicates the controller’s ability
UP
DOWN
to slew the inductor current higher in response to
increased load, and must always be greater than 1. As
h approaches 1, the absolute minimum dropout point,
the inductor current cannot increase as much during
each switching cycle, and V
SAG
unless additional output capacitance is used.
A reasonable minimum value for h is 1.5, but adjusting
this up or down allows trade-offs between V
capacitance, and minimum operating voltage. For a
given value of h, the minimum operating voltage can be
calculated as:
+
V
V
OUT
DROP
1
=
V
IN MIN
(
)
×
h
t
OFF MIN
(
)
1 -
K
where V
and V
are the parasitic voltage
DROP1
DROP2
drops in the discharge and charge paths (see the On-
Time One-Shot (TON) section), t
Electrical Characteristics, and K is taken from Table 1.
The absolute minimum input voltage is calculated with
h = 1.
______________________________________________________________________________________
If the calculated V
minimum input voltage, then the operating frequency
must be reduced or output capacitance added to
2
×
L
obtain an acceptable V
)
anticipated, calculate V
V
OUT
transient response.
A dropout design example follows:
V
= 2.5V
OUT
f
= 600kHz
SW
K = 1.7µs
t
OFF(MIN)
V
DROP1
h = 1.5
V
IN MIN
(
In applications where fast-load transients occur, the
output voltage changes instantly by R
)
DOWN
∆I
). The
LOAD
UP
put capacitors for such applications, and maximizes
the output-voltage AC and DC tolerance window in
tight-tolerance applications.
Figure 9 shows the connection of OUT and FB in a volt-
age-positioned circuit. In nonvoltage-positioned cir-
greatly increases,
cuits, the MAX8632 regulates at the output capacitor. In
voltage-positioned circuits, the MAX8632 regulates on
the inductor side of the voltage-positioning resistor.
, output
V
is reduced to:
OUT
SAG
V
OUT VPS
Careful PC board layout is critical to achieve low
switching losses and clean, stable operation. The
+
V
-
V
DROP
2
DROP
1
switching power stage requires particular attention. If
possible, mount all the power components on the top
side of the board, with their ground terminals flush
against one another. Follow these guidelines for good
PC board layout:
• Keep the high-current paths short, especially at the
is from the
OFF(MIN)
ground terminals. This practice is essential for sta-
ble, jitter-free operation.
• Keep the power traces and load connections short.
This practice is essential for high efficiency. Using
is greater than the required
IN(MIN)
. If operation near dropout is
SAG
to be sure of adequate
SAG
= 450ns
= V
= 100mV
DROP2
+
2 5
.
V
0 1
.
V
=
+
0 1
.
V
)
×
1 5
.
450
ns
1
-
µ
1 7
.
s
Voltage Positioning (Buck)
ESR
. Voltage positioning allows the use of fewer out-
=
V
-
R
(
)
OUT NO LOAD
(
_
)
POS
PC Board Layout Guidelines
=
-
0 1
.
V
4 3
.
V
× C
×
OUT
×
I
LOAD
25