STLDC08 STMicroelectronics, STLDC08 Datasheet - Page 16

• Manufacturer Part Number: STLDC08
• Description: Step-up controller for LED supply
• Manufacturer: STMicroelectronics

Application information
8
8.1
8.2
8.3
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Application information
LED current programming
The LED current is set by an external resistor connected between the FB pin and GND. The
following equation can be used to calculate the value of the R
the desired output current:
Equation 1
The feedback signal V
by the error amplifier. The internal reference has a guaranteed tolerance of 10 %. Tolerance
of the sense resistor adds additional error to the output voltage. 1 % resistors are
recommended.
Duty cycle
The controlled off-time architecture is a hysteretic mode control. Hysteretic operation
eliminates the need for small signal control loop compensation. When the converter runs in
continuous conduction mode (CCM) the controller adapts the T
duty cycle given by the following relationship:
Equation 2
where V
Equation 3
and VD is the forward voltage of the Schottky diode.
Inductor selection
As the hysteretic control scheme is inherently stable, the inductor value does not affect the
stability of the regulator. The switching frequency, peak inductor current, and allowable
ripple of the output current determine the value of the inductor.
LED manufacturers generally recommend a value for LED current ripple ranging from 5 % to
20 % of LED average current.
O
is the output voltage given by:
FB
is compared with the internal precision 100 mV voltage reference
Doc ID 18476 Rev 1
V
O
D
=
=
R
n
1
FB
×
−
V
V
( F
=
OUT
LED
I
LED
0
V
IN
1 .
+
)
+
V
D
V
FB
FB
ON
resistor which guarantees
time in order to obtain the
STLDC08