MAX8770GTL+T Maxim Integrated Products, MAX8770GTL+T Datasheet - Page 45

• Manufacturer Part Number: MAX8770GTL+T
• Description: IC CTLR PS 2/1PH QUICK PWM 40QFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8770GTL+T

• Applications: Controller, Intel IMVP-6
• Voltage - Input: 4 ~ 26 V
• Number Of Outputs: 1
• Voltage - Output: 0.125 ~ 1.5 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PWM Controller for IMVP-6+ CPU Core Power Supplies
CONFIDENTIAL INFORMATION – RESTRICTED TO INTEL
The output voltage-adjustable range for continuous-
conduction operation is restricted by the nonadjustable
minimum off-time one-shot and the number of phases.
For best dropout performance, use the slower (200kHz)
on-time settings. 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 propagation
delays introduce an error to the on-times. This error is
greater at higher frequencies. Also, keep in mind that
transient response performance of buck regulators
operated too close to dropout is poor, and bulk output
capacitance must often be added (see the V
tion in the Design 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
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
unless additional output capacitance is used.
A reasonable minimum value for h is 1.5, but adjusting
this up or down allows tradeoffs between V
capacitance, and minimum operating voltage. For a
given value of h, the minimum operating voltage can be
calculated as:
where V
is the parasitic voltage drops in the charge path (see
the On-Time One-Shot section) and t
the Electrical Characteristics table. The absolute mini-
mum input voltage is calculated with h = 1.
If the calculated V
imum input voltage, then reduce the operating frequency
or add output capacitance to obtain an acceptable V
If operation near dropout is anticipated, calculate V
be sure of adequate transient response.
Minimum Input-Voltage Requirements and
DROOP
V
MAX8770/MAX8771/MAX8772 Dual-Phase, Quick-
IN MIN
(
UP
/∆I
)
is the voltage-positioning droop, V
DOWN
IN(MIN)
=
______________________________________________________________________________________
⎡
⎢
⎢
⎣
V
VID
1
is an indicator of the ability to
is greater than the required min-
−
−
h
Dropout Performance
V
×
DROOP
SAG
t
OFF MIN SW
(
greatly increases
+
OFF(MIN)
)
V
f
CHG
SAG
SAG
⎤
⎥
⎥
⎦
UP
, output
is from
DOWN
SAG
equa-
). The
SAG
CHG
to
)
.
Dropout design example:
V
f
t
V
V
h = 1.5
Calculating again with h = 1 gives the absolute limit of
dropout:
Therefore, V
very large output capacitance, and a practical input
voltage with reasonable output capacitance would be
5.0V.
Careful PC board layout is critical to achieve low switching
losses and clean, stable operation. The switching power
stage requires particular attention (Figure 11). If possible,
mount all the power components on the top side of the
board with their ground terminals flush against one anoth-
er. Follow these guidelines for good PC board layout:
1) Keep the high-current paths short, especially at the
2) Connect all analog grounds to a separate solid cop-
3) Keep the power traces and load connections short.
4) Keep the high-current, gate-driver traces (DL, DH,
SW
OFF(MIN)
VID
DROOP
CHG
V
V
IN MIN
IN MIN
ground terminals. This is essential for stable, jitter-free
operation.
per plane, which connects to the GND pin of the
Quick-PWM controller. This includes the V
capacitor, REF and GNDS bypass capacitors, and
compensation (CCV) components.
This is essential for high efficiency. The use of thick
copper PC boards (2oz vs. 1oz) can enhance full-
load efficiency by 1% or more. Correctly routing PC
board traces is a difficult task that must be
approached in terms of fractions of centimeters,
where a single mΩ of excess trace resistance causes
a measurable efficiency penalty.
LX, and BST) short and wide to minimize trace resis-
tance and inductance. This is essential for high-
= 300kHz
(
(
= 1.15V
= 150mV (44A Load)
)
= 2.1mV/A x 44A = 92.4mV
)
= 375ns
=
=
IN
⎡
⎢
⎣
⎡
⎢
⎣
1
1
Applications Information
must be greater than 4.1V, even with
1 15
−
1 15
−
.
.
( .
( .
0 375
0 375
V
PC Board Layout Guidelines
V
®
−
−
IMVP-6 LICENSEES
µ
µ
92 4
92 4
s
s
.
.
×
×
mV
mV
1 0
1 5
.
.
+
+
×
×
150
150
300
300
mV
mV
kHz
kHz
)
)
CC
⎤
⎥ =
⎦
⎤
⎥ =
⎦
bypass
1 36
1 45
.
.
V
V
45