MAX17528GTJ+ Maxim Integrated Products, MAX17528GTJ+ Datasheet - Page 36

• Manufacturer Part Number: MAX17528GTJ+
• Description: IC PWM CTRLR STP-DWN 32TQFN-EP
• Manufacturer: Maxim Integrated Products
• Series: Quick-PWM™r

Specifications of MAX17528GTJ+

• Applications: Controller, Intel IMVP-6.5™ GMCH
• Voltage - Input: 4.5 ~ 5.5 V
• Number Of Outputs: 1
• Voltage - Output: 0.01 ~ 1.5 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

1-Phase Quick-PWM
Intel IMVP-6.5/GMCH Controllers
•
•
The switching frequency and operating point (% ripple
current or LIR) determine the inductor value as follows:
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Molded
cores are often the best choice, although powdered
iron and ferrite cores are inexpensive and can work
well at 300kHz. The core must be large enough not to
saturate at the peak inductor current (I
The inductor ripple current impacts transient-response
performance, especially at low V
Low inductor values allow the inductor current to slew
faster, replenishing charge removed from the output fil-
ter capacitors by a sudden load step. The amount of
output sag is also a function of the maximum duty fac-
tor, which can be calculated from the on-time and mini-
mum off-time. The worst-case output sag voltage can
be determined by:
36
Switching frequency: This choice determines the
basic trade-off between size and efficiency. The
optimal frequency is largely a function of maximum
input voltage due to MOSFET switching losses that
are proportional to frequency and V
mum frequency is also a moving target due to rapid
improvements in MOSFET technology that are mak-
ing higher frequencies more practical.
Inductor operating point: This choice provides
trade-offs between size vs. efficiency and transient
response vs. output noise. Low inductor values pro-
vide better transient response and smaller physical
size, but also result in lower efficiency and higher
output noise due to increased ripple current. The
minimum practical inductor value is one that causes
the circuit to operate at the edge of critical conduc-
tion (where the inductor current just touches zero
with every cycle at maximum load). Inductor values
lower than this grant no further size-reduction bene-
fit. The optimum operating point is usually found
between 20% and 50% ripple current.
______________________________________________________________________________________
L
=
I
PEAK
⎛
⎜
⎝
f
SW LOAD MAX
I
V
=
IN
I
LOAD MAX
−
V
(
OUT
(
Transient Response
)
LIR
Inductor Selection
)
⎛
⎜
⎝
IN
1
⎞
⎟
⎠
+
⎛
⎜
⎝
- V
V
LIR
V
OUT
2
PEAK
OUT
IN
⎞
⎟
⎠
IN
⎞
⎟
⎠
):
differentials.
2
. The opti-
where t
Electrical Characteristics table).
The amount of overshoot due to stored inductor energy
can be calculated as:
TIME and ILIM are used to control the slew rate and
current limit. TIME regulates to a fixed 2.0V. The
MAX17528 uses the TIME source current to set the
slew rate (dV
the faster the nominal output-voltage slew rate:
where R
TIME and ground.
The ILIM voltage determines the valley current-sense
threshold. When ILIM = V
preset 22.5mV (typ) current-limit threshold. In an
adjustable design, ILIM is connected to a resistive volt-
age-divider connected between TIME and ground. The
differential voltage between TIME and ILIM sets the
current-limit threshold (V
sense threshold is:
where the V
Characteristics table.
This allows design flexibility since the DCR sense cir-
cuit or sense resistor does not have to be adjusted to
meet the current limit as long as the current-sense volt-
age never exceeds 50mV. Keeping V
20mV to 40mV leaves room for future current-limit
adjustment.
V
SAG
=
OFF(MIN)
TIME
Current-Limit and Slew-Rate Control
dV
2
L
C
TARGET
LIMIT
(
OUT OUT
∆
TARGET
is the sum of resistance values between
I
LOAD(MAX)
V
SOAR
V
V
tolerances are defined in the Electrical
LIMIT
is the minimum off-time (see the
/
/dt). The higher the source current,
dt
≈
⎡
⎢
⎢
⎣
=
⎛
⎜
⎝
=
(
(
12 5
∆
)
V
V
2
LIMIT
2
IN
I
LOAD MAX
TIME
.
C
CC
⎡
⎢
⎣
mV µs
−
OUT OUT
⎛
⎝ ⎜
, the controller uses the
V
10
V
V
), so the valley current-
OUT SW
OUT SW
(
−
IN
/
V
V
V
ILIM
IN
(TIME and ILIM)
t
)
×
)
t
)
⎛
⎝ ⎜
2
71 5 Ω
L
R
⎞
⎠ ⎟
LIMIT
⎞
⎟ −
⎠
TIME
+
.
t
k
OFF
t t
OFF MIN
⎞
⎠ ⎟
between
(M M IN
(
)
)
⎤
⎥
⎦
⎤
⎥
⎥
⎦