EVALED2000P STMicroelectronics, EVALED2000P Datasheet - Page 24

• Manufacturer Part Number: EVALED2000P
• Description: LED Lighting Development Tools LED2000 3A 850KHz 3.0V to 18V Eval BRD
• Manufacturer: STMicroelectronics

Specifications of EVALED2000P

• Product Category: LED Lighting Development Tools
• Rohs: yes
• Product: Evaluation Boards
• Operating Supply Voltage: 3 V to 18 V
• For Use With: LED2000

Application information
7.1.3
24/40
Equation 27
Example (see
V
A lower inductor value maximizes the inductor current slew rate for better dimming
performance.
Equation 28
which is satisfied selecting a10 H inductor value.
The output capacitor value must be dimensioned according to
Finally, given the selected inductor value, a 2.2 F ceramic capacitor value keeps the LED
current ripple ratio lower than the 2% of the nominal current. An output ceramic capacitor
type (negligible ESR) is suggested to minimize the ripple contribution given a fixed capacitor
value.
Table 6.
Input capacitor
The input capacitor must be able to support the maximum input operating voltage and the
maximum RMS input current.
Since step-down converters draw current from the input in pulses, the input current is
squared and the height of each pulse is equal to the output current. The input capacitor
must absorb all this switching current, whose RMS value can be up to the load current
divided by two (worst case, with duty cycle of 50%). For this reason, the quality of these
capacitors must be very high to minimize the power dissipation generated by the internal
ESR, thereby improving system reliability and efficiency. The critical parameter is usually the
RMS current rating, which must be higher than the RMS current flowing through the
capacitor. The maximum RMS input current (flowing through the input capacitor) is:
Equation 29
where is the expected system efficiency, D is the duty cycle and I
current. Considering = 1 this function reaches its maximum value at D = 0.5 and the
Wurth Elektronik
Coilcraft
I
IN
RMS
=12 V, I
I
Manufacturer
RIPPLE
=
------------
I
LED
I
I
O
L
LED
=
s=j
Inductor selection
0.5
D
Equation 26
=700 mA,
Section Example
–
2
----------------- -
=
D
2
+
I
RIPPLE_SPEC
D
------ -
2
2
ILED
becomes:
WE-HCI 7040
WE-HCI 7050
Doc ID 023432 Rev 3
XPL 7030
/I
Series
LED
1):
=2%, V
FW_LED
Inductor value (µH)
=3.5 V, n
4.9 to 10
2.2 to 10
1 to 4.7
LED
=2.
Equation
O
is the output DC
Saturation current (A)
27.
20 to 4.0
29 to 7.2
20 to 7
LED2000