MAX17036 Maxim Integrated Products, MAX17036 Datasheet - Page 35

• Manufacturer Part Number: MAX17036
• Description: (MAX17030 / MAX17036) 1/2/3-Phase Quick-PWM IMVP-6.5 VID Controllers
• Manufacturer: Maxim Integrated Products

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However, it can indicate the possible presence of loop
instability due to insufficient ESR. Loop instability can
result in oscillations at the output after line or load
steps. Such perturbations are usually damped, but can
cause the output voltage to rise above or fall below the
tolerance limits.
The easiest method for checking stability is to apply a
very fast 10% to 90% max load transient and carefully
observe the output voltage ripple envelope for over-
shoot and ringing. It can help to simultaneously monitor
the inductor current with an AC current probe. Do not
allow more than one cycle of ringing after the initial
step-response under/overshoot.
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. For a dual-phase controller, the
worst-case output sag voltage can be determined by:
and:
where t
Electrical Characteristics ), T
switching period, and η
active phases. K = 66% when N
when N
droop ∆I
The capacitive soar voltage due to stored inductor
energy can be calculated as:
where η
actual peak of the soar voltage is dependent on the
time where the decaying ESR step and rising capaci-
tive soar is at its maximum. This is best simulated or
measured. For the MAX17036 with transient suppres-
sion, contact Maxim directly for application support to
determine the output capacitance requirement.
V
SAG
TOTAL
PH
OFF(MIN)
LOAD(MAX)
≈
= 2. V
V
2η
L
SOAR
is the total number of active phases. The
(
TOTAL OUT OUT
∆
T
I
MIN
SAG
______________________________________________________________________________________
LOAD(MAX)
is the minimum off-time (see the
x R
≈
2η
C
=
must be less than the transient
DROOP
(
t
∆
TOTAL OUT OUT
ON
TOTAL
I
LOAD MAX
V
+
)
Transient Response
2
.
t
OFF MIN
SW
C
(
is the total number of
PH
IN
×
(
is the programmed
⎡ ⎣
- V
= 3, and K = 100%
)
KT
V
)
2
)
OUT
S S W
L
T
MIN
−
differentials.
T
MIN
⎤ ⎦
IMVP-6.5 VID Controllers
1/2/3-Phase Quick-PWM
The input capacitor must meet the ripple current
requirement (I
The multiphase Quick-PWM controllers operate out-of-
phase, reducing the RMS input. For duty cycles less
than 100%/ η
can be determined by the following equation:
where η
switching regulators. The worst-case RMS current
requirement occurs when operating with V
2 η
fies to I
capacitor that exhibits less than +10°C temperature rise
at the RMS input current for optimal circuit longevity.
Most of the following MOSFET guidelines focus on the
challenge of obtaining high load-current capability
when using high-voltage (> 20V) AC adapters.
The conduction loss in the high-side MOSFET (N
function of the duty factor, with the worst-case power
dissipation occurring at the minimum input voltage:
where η
Calculating the switching losses in the high-side
MOSFET (N
quantifying factors that influence the turn-on and turn-
off times. These factors include the internal gate resis-
tance, gate charge, threshold voltage, source
inductance, and PCB layout characteristics. The follow-
ing switching-loss calculation provides only a very
rough estimate and is no substitute for breadboard
evaluation, preferably including verification using a
thermocouple mounted on N
where C
Q
MOSFET, and I
current (2.2A typ).
I
RMS
G(SW)
TOTAL
PD (NH Resistive) =
PD (NH Switching) =
=
⎛
⎜
⎝
TOTAL
RMS
V
OSS
η
TOTAL
is the charge needed to turn on the N
OUT
TOTAL IN
I
LOAD
H
OUTPH
is the N
= 0.5 x I
) is difficult since it must allow for difficult
. At this point, the above equation simpli-
RMS
is the total number of phases.
High-Side MOSFET Power Dissipation
GATE
V
is the total number of out-of-phase
) imposed by the switching currents.
⎞
⎟
⎠
per phase, the I
is the peak gate-drive source/sink
H
η
Input Capacitor Selection
LOAD
+
Power-MOSFET Selection
⎛
⎝ ⎜
MOSFET’s output capacitance,
TOTAL OUT
V
C
⎛
⎝ ⎜
V
OUT
V I
OSS IN SW
IN
IN LOAD SW
/ η
H
η
V
:
V
⎞
⎠ ⎟ η
TOTAL
TOTAL
2
⎛
⎝ ⎜
2
I
LOAD
TOTA
f
f
(
V
. Choose an input
IN
RMS
⎞
⎠ ⎟
L L
−
⎛
⎜
⎝
⎞
⎠ ⎟
η
Q Q
2
I
requirements
TOT
GATE
G SW
R
(
DS ON
A A L OUT
(
)
V
⎞
⎟
⎠
H
) is a
)
IN
35
)
=
H