LED5000PHR STMicroelectronics, LED5000PHR Datasheet - Page 24

• Manufacturer Part Number: LED5000PHR
• Description: Current & Power Monitors & Regulators 3A monolithic Conv 850kHz Synch
• Manufacturer: STMicroelectronics

Specifications of LED5000PHR

• Rohs: yes
• Product: Current Regulators
• Supply Voltage - Max: 48 V
• Supply Voltage - Min: 5.5 V
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: SMD/SMT
• Package / Case: HPSO-8
• Accuracy: +/- 3 %
• Input Voltage Range: 5.5 V to 48 V
• Output Current: 23 uA
• Sensing Method: High or Low Side
• Supply Current: 1.7 mA

Application notes - buck conversion
24/51
The LED ripple current can be calculated as the inductor ripple current ratio flowing into the
output impedance using the Laplace transform (see
Equation 27
where the term 8/ 2 represents the main harmonic of the inductor current ripple (which has
a triangular shape) and I
Equation 28
so L value can be calculated as:
Equation 29
where T
As a consequence the lower is the inductor value (so higher the current ripple), the higher
would be the C
A general rule to dimension L value is:
Equation 30
Finally the required output capacitor value can be calculated equalizing the LED current
ripple specification with the module of the Fourier transformer (see
at f
Equation 31
Example (see
V
A lower inductor value maximizes the inductor current slew rate for better dimming
performance.
IN
SW
=48 V, I
frequency.
OFF
LED
is the OFF time of the embedded high switch, given by 1-D.
Equation 30
=700 mA,
OUT
Chapter 5.6
value to meet the specification.
I
RIPPLE
I
L
=
V
--------------
L
ILED
becomes:
):
OUT
L
is the inductor current ripple.
s
Doc ID 023951 Rev 1
/I
=
I
RIPPLE
LED
-------------------------------------------------------------------------------------------------------------------
1
T
OFF
+
=2%, V
s
-----
8
2
s=j
=
R
n
-------------------------------------------------------------------- -
---------- - 0.5
I
S
LED
LED
FW_LED
I
I
+
L
L
ESR
=
V
1
FW_LED
+
=3.7 V, n
+
I
RIPPLE_SPEC
s
n
Figure 11
L
LED
ESR
+
200mV
LED
R
LED
):
C
=10
OUT
Equation 27
T
C
OFF
OUT
) calculated
LED5000