LED7708 STMicroelectronics, LED7708 Datasheet - Page 26

• Manufacturer Part Number: LED7708
• Description: LED Lighting Drivers 16 Ch 85mA LED 3.6 to 36V 250kHz
• Manufacturer: STMicroelectronics

Specifications of LED7708

• Rohs: yes

Recommended operating conditions
8.3.4
26/53
Figure 6.
The SLOPE pin allows to properly set the amount of slope compensation connecting a
simple resistor R
starts at 35% (typ.) of each switching period and its slope is given by the following equation:
Equation 7
where K
To avoid sub-harmonic instability, the compensating slope should be at least half the slope
of the inductor current during the off-phase when the duty cycle is greater than 50%. The
value of R
Equation 8
External MOSFET control
The LED7708 employs an external MOSFET as the power switch for the boost converter.
The internal gate driver is capable of sourcing and sinking up to 1 A and it is supplied
through the VDR pin, internally connected to the +5 V LDO. A 1 µF decoupling capacitor,
connected between the VDR pin and PGND, is highly recommended. When an external +5
V supply is available, the whole device can be supplied by connecting both the VDR and VIN
pins to this rail.
S
= 4.0 s
SLOPE
Effect of slope compensation on small inductor current perturbation
(D>0.5)
SLOPE
can be calculated according to
-1
and S
between the SLOPE pin and the output. The compensation ramp
E
R
is the slope ramp in [A/s].
SLOPE
Doc ID 022698 Rev 1
≤
2
----------------------------------------------------------------------------------------
⋅
K
S
s
E
⋅
=
L
(
-------------------- -
R
⋅
V
SLOPE
OUT
(
K
V
Equation
S
OUT
–
V
–
IN
V
)
IN
8.
–
0.7V
)
LED7708