MAX8632ETI+T Maxim Integrated Products, MAX8632ETI+T Datasheet - Page 18

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

Specifications of MAX8632ETI+T

• 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, 2.5 V, 0.7 V to 5.5 V
• Output Current: 15 A
• Input Voltage: 2 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

• Switching Frequency. This choice determines the
• Inductor Operating Point. This choice provides trade-
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
directly to OUT for a fixed 0.7V output.
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:
where V
and V
Integrated DDR Power-Supply Solution for
Desktops, Notebooks, and Graphic Cards
18
current-limit circuit. The continuous load current
(I
drives the selection of input capacitors, MOSFETs,
and other critical heat-contributing components.
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-
al to frequency and V
also a moving target due to rapid improvements in
MOSFET technology that are making higher frequen-
cies more practical.
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.
LOAD
Setting the Buck Regulator Output (V
______________________________________________________________________________________
RIPPLE
FB
V
) determines the thermal stresses and thus
RIPPLE
V
Setting the Output Voltage (Buck)
OUT
is 0.7V, R
is:
DD
for a fixed 1.8V output, or connect FB
=
=
LIR
V
FB
C
Resistive Voltage-Divider at FB
and R
×



IN
1
I
2
LOAD MAX
+
. The optimum frequency is
R
R
D
Preset Output Voltages
D
C
(
are shown in Figure 6,

 +

)
V
RIPPLE
×
2
R
ESR
OUT
) with a
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
higher than V
from VTT to VTTS. The maximum value for VTT is V
V
= +85°C.
The termination reference voltage (VTTR) tracks 0.5 x
V
The switching frequency and inductor operating point
determine the inductor value as follows:
For example: I
2.5V, f
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
Figure 5. Dual-Mode Feedback Decoder
DROPOUT
REFIN
Setting the VTT and VTTR Voltages (LDO)
REF (2.0V)
REFIN
0.1V
SW
FB
.
L
L
= 600kHz, 30% ripple current or LIR = 0.3:
=
/ 2. Secondly, VTT can be forced to regulate
=
where V
12
REFIN
V
AMPLIFIER
IN
LOAD(MAX)
V
ERROR
×
×
2 5
TO
/ 2 by connecting a resistive divider
DROPOUT
.
V
600
f
SW
OUT
V
Inductor Selection (Buck)
kHz
(
12
×
(
V
= 12A, V
V
I
LOAD MAX
IN
×
- 2.5V)
= I
12
-
VTT
V
(
A
OUT
MAX8632
×
× 0.3Ω (max) at T
IN
)
)
0 3
= 12V, V
×
.
LIR
≈
1
µ
H
OUT
(FIXED)
(FIXED)
VTTI
1.8V
2.5V
OUT
=
A
-