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
current-limit circuit. The continuous load current
(I
) determines the thermal stresses and thus
LOAD
drives the selection of input capacitors, MOSFETs,
and other critical heat-contributing components.
• Switching Frequency. This choice determines the
basic trade-off between size and efficiency. The opti-
mal frequency is largely a function of maximum input
voltage, due to MOSFET switching losses proportion-
2
al to frequency and V
. The optimum frequency is
IN
also a moving target due to rapid improvements in
MOSFET technology that are making higher frequen-
cies more practical.
• Inductor Operating Point. This choice provides trade-
offs: size vs. efficiency and transient response vs. out-
put ripple. Low inductor values provide better
transient response and smaller physical size but also
result in lower efficiency and higher output ripple due
to increased ripple currents. The minimum practical
inductor value is one that causes the circuit to operate
at the edge of critical conduction (where the inductor
current just touches zero with every cycle at maximum
load). Inductor values lower than this grant no further
size-reduction benefit. The optimum operating point is
usually found between 20% and 50% ripple current.
When pulse skipping (SKIP = low at light loads), the
inductor value also determines the load-current value
at which PFM/PWM switchover occurs.
Setting the Output Voltage (Buck)
Preset Output Voltages
The MAX8632 dual-mode operation allows the selection
of common voltages without requiring external compo-
nents (Figure 5). Connect FB to GND for a fixed 2.5V
output, to AV
for a fixed 1.8V output, or connect FB
DD
directly to OUT for a fixed 0.7V output.
Setting the Buck Regulator Output (V
Resistive Voltage-Divider at FB
The buck-regulator output voltage can be adjusted from
0.7V to 5.5V using a resistive voltage-divider (Figure 6).
The MAX8632 regulates FB to a fixed reference voltage
(0.7V). The adjusted output voltage is:
R
C
=
+
 +
V
V
1
OUT
FB
R
D
where V
is 0.7V, R
and R
are shown in Figure 6,
FB
C
D
and V
is:
RIPPLE
=
×
V
LIR
I
RIPPLE
LOAD MAX
(
18
______________________________________________________________________________________
Setting the VTT and VTTR Voltages (LDO)
The termination power-supply output (VTT) can be set by
two different methods. First, the VTT output can be con-
nected directly to the VTTS input to force VTT to regulate
to V
/ 2. Secondly, VTT can be forced to regulate
REFIN
higher than V
from VTT to VTTS. The maximum value for VTT is V
V
DROPOUT
= +85°C.
The termination reference voltage (VTTR) tracks 0.5 x
V
.
REFIN
The switching frequency and inductor operating point
determine the inductor value as follows:
=
L
For example: I
2.5V, f
= 600kHz, 30% ripple current or LIR = 0.3:
SW
=
L
Find a low-loss inductor with the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite
cores are often the best choice, although powdered
iron is inexpensive and can work well at frequencies up
) with a
OUT
FB
REF (2.0V)
V
RIPPLE
2
0.1V
×
R
)
ESR
Figure 5. Dual-Mode Feedback Decoder
/ 2 by connecting a resistive divider
REFIN
× 0.3Ω (max) at T
where V
= I
DROPOUT
VTT
Inductor Selection (Buck)
(
)
V
V
-
V
OUT
IN
OUT
×
×
×
V
f
I
LIR
IN
SW
LOAD MAX
(
)
= 12A, V
= 12V, V
LOAD(MAX)
IN
2 5
.
V
(
12
V
- 2.5V)
µ
1
H
×
×
×
12
V
600
kHz
12
A
0 3
.
MAX8632
TO
ERROR
AMPLIFIER
-
VTTI
A
=
OUT
OUT
1.8V
(FIXED)
2.5V
(FIXED)