STEVAL-ISA038V1 STMicroelectronics, STEVAL-ISA038V1 Datasheet - Page 20

BOARD EVALUATION W/L6728

STEVAL-ISA038V1

Manufacturer Part Number
STEVAL-ISA038V1
Description
BOARD EVALUATION W/L6728
Manufacturer
STMicroelectronics
Type
DC/DC Switching Converters, Regulators & Controllersr
Datasheets

Specifications of STEVAL-ISA038V1

Design Resources
STEVAL-ISA038V1 Schematic STEVAL-ISA038V1 Bill of Material
Main Purpose
DC/DC, Step Down
Outputs And Type
1, Non-Isolated
Voltage - Output
1.25V
Current - Output
5A
Voltage - Input
5 ~ 12V
Regulator Topology
Buck
Frequency - Switching
300kHz
Board Type
Fully Populated
Utilized Ic / Part
L6728
Input Voltage
5 V to 12 V
Output Voltage
1.25 V
Product
Power Management Modules
Silicon Manufacturer
ST Micro
Silicon Core Number
L6728D
Kit Application Type
Power Management - Voltage Regulator
Application Sub Type
Step Down DC/DC Controller
Kit Contents
Board
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Power - Output
-
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
For Use With/related Products
L6728
Other names
497-8228
STEVAL-ISA038V1

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
STEVAL-ISA038V1
Manufacturer:
STMicroelectronics
Quantity:
1
Application information
11.2
11.3
20/31
Output capacitor(s)
The output capacitors are basic components to define the ripple voltage across the output
and for the fast transient response of the power supply. They depend on the output voltage
ripple requirements, as well as any output voltage deviation requirement during a load
transient.
During steady-state conditions, the output voltage ripple is influenced by both the ESR and
capacitive value of the output capacitors as follow:
Where ΔI
takes in consideration the output capacitor charge and discharge as a consequence of the
inductor current ripple.
During a load variation, the output capacitors supplies the current to the load or absorb the
current stored into the inductor until the converter reacts. In fact, even if the controller
recognizes immediately the load transient and sets the duty cycle at 80 % or 0 %, the
current slope is limited by the inductor value. The output voltage has a drop that also in this
case depends on the ESR and capacitive charge/discharge as follow:
Where ΔV
(
MLCC capacitors have typically low ESR to minimize the ripple but also have low
capacitance that do not minimize the voltage deviation during dynamic load variations. On
the contrary, electrolytic capacitors have big capacitance to minimize voltage deviation
during load transients while they does not show the same ESR values of the MLCC resulting
then in higher ripple voltages. For these reasons, a mix between electrolytic and MLCC
capacitor is suggested to minimize ripple as well as reducing voltage deviation in dynamic
mode.
Input capacitors
The input capacitor bank is designed considering mainly the input rms current that depends
on the output deliverable current (I
The equation reaches its maximum value, I
input capacitor ESR and, in worst case, are:
ΔV
ΔV
ΔV
ΔV
I
P
rms
D
MAX
=
OUT_ESR
OUT_C
OUT_ESR
OUT_C
=
ESR
I
OUT
V
IN
L
=
=
L
(
is the inductor current ripple. In particular, the expression that defines ΔV
=
=
I
ΔI
ΔI
is the voltage applied to the inductor during the transient response
OUT
V
L
OUT
ΔI
ΔI
D
OUT
L
OUT
-------------------------------------- -
8 C
2 ⁄
(
1 D
ESR
)
------------------------------------- -
2 C
for the load appliance or V
2
OUT
ESR
L ΔI
1
)
OUT
F
OUT
SW
ΔV
L
OUT
) and the duty-cycle (D) for the regulation as follow:
OUT
OUT
/2, with D = 0.5. The losses depends on the
for the load removal).
OUT_C
L6728

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