MAX17528GTJ+ Maxim Integrated Products, MAX17528GTJ+ Datasheet - Page 21

• 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

The Quick-PWM control architecture is a pseudo-fixed-
frequency, constant-on-time, current-mode regulator
with voltage feed-forward (Figure 3). This architecture
relies on the output filter capacitor’s ESR and the load
regulation to provide the proper current-mode compen-
sation, so the resulting feedback ripple voltage provides
the PWM ramp signal. The control algorithm is simple:
the high-side switch on-time is determined solely by a
one-shot whose period is inversely proportional to input
voltage, and directly proportional to the feedback volt-
age (see the On-Time One-Shot section). Another one-
shot sets a minimum off-time. The on-time one-shot
triggers when the error comparator goes low (the feed-
back voltage drops below the target voltage), the
inductor current is below the valley current-limit thresh-
old, and the minimum off-time one-shot times out.
The Quick-PWM controller requires an external +5V bias
supply in addition to the battery. Typically, this +5V bias
supply is the notebook’s 95%-efficient, +5V system sup-
ply. Keeping the bias supply external to the IC improves
efficiency and eliminates the cost associated with the
+5V linear regulator that would otherwise be needed to
supply the PWM circuit and gate drivers. If stand-alone
capability is needed, the +5V bias supply can be gen-
erated with an external linear regulator.
The +5V bias supply must provide V
troller) and V
current drawn is:
where I
table, f
Q
charge specification limits at V
V
is a fixed +4.5V to +5.5V supply. If the +5V bias supply is
powered up prior to the battery supply, the enable signal
(SHDN going from low to high) must be delayed until the
battery voltage is present to ensure startup.
Connect a resistor (R
the switching period (t
IN
G(HIGH)
and V
SW
CC
I
Controllers with Input Feed-Forward
BIAS
DD
is the switching frequency, and Q
are the MOSFET data sheet’s total gate-
is provided in the Electrical Characteristics
t
SW
can be connected if the input power source
Free-Running, Constant On-Time
DD
=
+5V Bias Supply (V
I
CC
= 16.3pF x (R
(gate-drive power), so the maximum
______________________________________________________________________________________
+
Switching Frequency (TON)
TON
f
SW
SW
Detailed Description
(
) between TON and V
= 1/f
Q
G LOW
(
TON
SW
GS
):
= 5V.
)
+ 6.5kΩ)
+
Q
Intel IMVP-6.5/GMCH Controllers
G HIGH
CC
CC
(
(PWM con-
and V
G(LOW)
)
)
IN
to set
DD
and
)
A 96.75kΩ to 303.25kΩ corresponds to switching peri-
ods of 1.67µs (600kHz) to 5µs (200kHz), respectively.
High-frequency (over 500kHz) operation optimizes the
application for the smallest component size, trading off
efficiency due to higher switching losses. This may be
acceptable in ultra-portable devices where the load
currents are lower and the controller is powered from a
lower voltage supply. Low-frequency (under 300kHz)
operation offers the best overall efficiency at the
expense of component size and board space.
The TON input includes open-circuit protection to avoid
long, uncontrolled on-times that could result in an over-
voltage condition on the output. The MAX17528 detects
an open-circuit fault if the TON current drops below
10µA for any reason—the TON resistor (R
unpopulated, a high resistance value is used, the input
voltage is low, etc. Under these conditions, the
MAX17528 stops switching (DH and DL pulled low) and
immediately sets the fault latch. Toggle SHDN or cycle
the V
and reactivate the controller.
The core contains a fast, low-jitter, adjustable one-shot
that sets the high-side MOSFET’s on-time. The one-shot
varies the on-time in response to the input and feedback
voltages. The main high-side switch on-time is inversely
proportional to the input voltage as measured by the R
input, and proportional to the feedback voltage (V
where the switching period (t
resistor between V
This algorithm results in a nearly constant switching fre-
quency despite the lack of a fixed-frequency clock
generator. The benefits of a constant switching fre-
quency are twofold: first, the frequency can be select-
ed to avoid noise-sensitive regions, such as the 455kHz
IF band; second, the inductor ripple-current operating
point remains relatively constant, resulting in easy
design methodology and predictable output voltage
ripple. The on-time one-shots have good accuracy at
the operating points specified in the Electrical
Characteristics table. On-times at operating points far
removed from the conditions specified in the Electrical
Characteristics table can vary over a wider range.
CC
1-Phase Quick-PWM
power supply below 0.5V to clear the fault latch
IN
TON Open-Circuit Fault Protection
t
ON
and TON.
=
t
SW
⎛
⎝ ⎜
SW
V
V
FB
IN
= 1/f
⎞
⎠ ⎟
On-Time One-Shot
SW
) is set by the
FB
TON
):
TON
) is
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