max5066auit Maxim Integrated Products, Inc., max5066auit Datasheet - Page 19

• Manufacturer Part Number: max5066auit
• Description: Max5066 Configurable, Single-/dual-output, Synchronous Buck Controller For High-current Applications
• Manufacturer: Maxim Integrated Products, Inc.

Table 2. Low-Side MOSFET Losses
Note: The gate drive losses are distributed between the drivers and the MOSFETs in the ratio of the gate driver’s resistance and the
MOSFET’s internal gate resistance.
load step. Use a combination of SP polymer and
ceramic capacitors for better transient load and rip-
ple/noise performance.
Keep the maximum output-voltage deviation less than
or equal to the adaptive voltage-positioning window
(∆V
tion each from the output capacitance discharge and
the voltage drop across the ESR (∆V
+ ∆V
the required ESR and capacitance value:
where I
t
Controller response time depends on the control-loop
bandwidth. C
The average current-mode control technique of the
MAX5066 accurately limits the maximum average out-
put current per phase. The MAX5066 senses the volt-
age across the sense resistor and limits the maximum
inductor current accordingly. Use the equations below
to calculate the current-sense resistor values:
Conduction Loss
Gate Drive Loss
RESPONSE
Configurable, Single-/Dual-Output, Synchronous
OUT
Q_OUT
Buck Controller for High-Current Applications
LOSS
). During a load step, assume a 50% contribu-
LOAD_STEP
R
C
). Use the following equations to calculate
ESR OUT
OUT
is the response time of the controller.
OUT
I
_
LOAD MAX
=
is C6 and C7 in Figure 6.
______________________________________________________________________________________
Losses associated with MOSFET on-time, I
is a function of load current and duty cycle.
Losses associated with charging and
discharging the gate of the MOSFET every
cycle. There is no Q
MOSFET due to the zero-voltage turn-on. The
charge involved is (Q
I
LOAD STEP
is the step in load current and
(
=
I
∆
LOAD STEP
_
V
)
ESR OUT
∆
=
V
Q OUT
24 75
_
_
_
×
.
R
t
DESCRIPTION
RESPONSE
SENSE
×
GD
OUT
G
10
Current Limit
charging involved in this
- Q
−
3
GD
= ∆V
).
ESR_OUT
RMS
Due to tolerances involved, the minimum average volt-
age at which the voltage across the current-sense
resistor is clamped is 20.4mV. Therefore, the minimum
average current limit is set at:
For example, the current-sense resistor:
for a maximum output current of 10A. The standard
value is 2mΩ. Also, adjust the value of the current-
sense resistor to compensate for parasitics associated
with the PC board. Select a noninductive resistor with
appropriate wattage rating.
The second type of current limit is the peak current limit
as explained in the Peak-Current Comparator section.
The third current-protection circuit is the hiccup fault
protection as explained in the Hiccup Fault Protection
section. The average current during a short at the out-
put is given by:
The MAX5066 limits the reverse current when the output
capacitor voltage is higher than the preset output volt-
age. Calculate the maximum reverse current limit based
on V
CLAMP_LO
P
P
where I
GATEDRIVE
CONDUCTION
I
AVG SHORT
R
and the current-sense resistor R
SENSE
I
(
LIMIT MIN
RMS
SEGMENT LOSSES
(
=
=
≈
)
V
20 4
=
=
DD
)
V
10
I
1 41
.
RMS
IN
=
Reverse Current Limit
.
×
A
mV
20 4
−
R
V
(
IN
Q
2
SENSE
V
.
R
×
OUT
G
×
=
SENSE
10
R
×
2 04
−
.
DS ON
Q
−
10
×
GD
3
(
m
I
LOAD
−
3
Ω
)
)
×
f
SW
SENSE
.
19