a5975d STMicroelectronics, a5975d Datasheet - Page 40

• Manufacturer Part Number: a5975d
• Description: Up To 3 A Step-down Switching Regulator For Automotive Applications
• Manufacturer: STMicroelectronics

Application information
Figure 29. 350 mA LED boost current source
40/50
The device is powered from the output voltage so the maximum voltage drop across the
LEDs and resistor sense is 36 V.
The output voltage is given by:
Equation 42
where the ideal duty cycle D for the boost converter is:
Equation 43
As for positive and inverting buck-boost (see
real duty cycle must be used to calculate the switch current level.
The peak current flowing in the embedded switch is:
Equation 44
while its average current is equal to:
Equation 45
This is due to the fact that the current flowing through the internal power switch is delivered
to the output only during the OFF phase.
I
SW
=
Doc ID 018760 Rev 1
I
-------------- -
1 D
LOAD
–
+
D
V
I
------------------- -
I
RIPPLE
SW
OUT
=
2
V
----------------------------- -
=
OUT
Section 8.7
=
V
I
-------------- -
1 D
LOAD
OUT
------------ -
1 D
=
V
–
–
–
IN
I
-------------- -
V
1 D
LOAD
IN
–
+
and
---------- -
2 L
V
⋅
IN
Section
⋅
---------
f
SW
D
8.8.) the measured
A5975D