EVAL5985 STMicroelectronics, EVAL5985 Datasheet - Page 14

• Manufacturer Part Number: EVAL5985
• Description: BOARD EVAL FOR L5985
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of EVAL5985

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 3.3V
• Current - Output: 2A
• Voltage - Input: 3.3 ~ 18V
• Regulator Topology: Buck
• Frequency - Switching: 500kHz
• Board Type: Fully Populated
• Utilized Ic / Part: L5985
• Input Voltage: 2.9 V to 18 V
• Output Voltage: 0.6 V to 16 V
• Product: Power Management Modules
• Silicon Manufacturer: ST Micro
• Silicon Core Number: L5985
• Kit Application Type: Power Management - Voltage Regulator
• Application Sub Type: Step Down Switching Regulator
• 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: L5985
• Other names: 497-6387; EVAL5985

Application information
5
5.1
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Application information
Input capacitor selection
The capacitor connected to the input has to be capable to support the maximum input
operating voltage and the maximum RMS input current required by the device. The input
capacitor is subject to a pulsed current, the RMS value of which is dissipated over its ESR,
affecting the overall system efficiency.
So the input capacitor must have a RMS current rating higher than the maximum RMS input
current and an ESR value compliant with the expected efficiency.
The maximum RMS input current flowing through the capacitor can be calculated as:
Equation 3
Where Io is the maximum DC output current, D is the duty cycle, η is the efficiency.
Considering η = 1, this function has a maximum at D = 0.5 and it is equal to Io/2.
In a specific application the range of possible duty cycles has to be considered in order to
find out the maximum RMS input current. The maximum and minimum duty cycles can be
calculated as:
Equation 4
and
Equation 5
Where V
the internal PDMOS.
In
Table 6.
Table 6
Manufacturer
MURATA
F
TDK
some multi layer ceramic capacitors suitable for this device are reported:
is the forward voltage on the freewheeling diode and V
Input capacitors
Doc ID 13006 Rev 5
GRM31
GRM55
Series
C3225
I
RMS
D
D
MAX
MIN
=
I
=
O
=
⋅
------------------------------------- -
V
------------------------------------ -
V
INMAX
V
V
INMIN
D
OUT
OUT
–
2 D
-------------- -
+
Cap value (μF)
⋅
+
–
–
η
V
V
V
V
2
F
SW
SW
F
+
D
------ -
η
10
10
10
2
2
SW
is voltage drop across
Rated voltage (V)
25
25
25
L5985