STEVAL-ILL021V1 STMicroelectronics, STEVAL-ILL021V1 Datasheet - Page 14

• Manufacturer Part Number: STEVAL-ILL021V1
• Description: BOARD EVAL LCD BACKLIGHT LED7707
• Manufacturer: STMicroelectronics

Specifications of STEVAL-ILL021V1

• Design Resources: STEVAL-ILL021V1 Bill of Material STEVAL-ILL021V1 Schematic
• Current - Output / Channel: 85mA
• Outputs And Type: 6, Non-Isolated
• Voltage - Output: 36 V
• Features: Dimmable, Extra 5V Output
• Voltage - Input: 4.5 ~ 36 V
• Utilized Ic / Part: LED7707
• Description/function: LCD backlight demonstration board
• Operating Voltage: 4.5 V to 36 V
• Product: Display Modules
• Core Chip: LED7707
• No. Of Outputs: 1
• Output Voltage: 36V
• Dimming Control Type: PWM
• Mcu Supported Families: LED7707
• Lead Free Status / RoHS Status: Lead free by exemption / RoHS compliant by exemption
• For Use With/related Products: LED7707
• Other names: 497-10044

Operation description
5.1.4
5.1.5
14/47
reacts by increasing the output voltage. When it reaches the floating row detection (FRD)
threshold (which coincides with the OVP threshold, see
managed according to
2.4 V threshold, the start-up finishes and all the protections turn active. The soft-start
capacitor C
Equation 2
Where I
Over-voltage protection
An adjustable over-voltage protection is available. It can be set feeding the OVSEL pin with a
partition of the output voltage. The voltage of the central tap of the divider is thus compared
to a fixed 1.145 V threshold. When the voltage of the OVSEL pin exceeds the OV threshold,
the switching activity is suspended. It is resumed as OVSEL returns below the OV threshold.
A 10 mV hysteresis is provided. No device turn-off is performed. Normally, the value of the
high-side resistors of the divider is in the order of 100 kΩ to reduce the output capacitor
discharge when the boost converter is off (during the off phase of the dimming cycle),
whereas the low-side resistor can be calculated as:
Equation 3
An additional filtering capacitor C
improve noise rejection at the OVSEL pin (see
Figure 9.
Switching frequency selection and synchronization
The switching frequency of the boost converter can be set in the 250 kHz-1 MHz range by
connecting the FSW pin to ground through a resistor. Calculation of the setting resistor is
made using equation 4 and should not exceed the 100 kΩ-400 kΩ range.
SS
= 5 µA and t
SS
OVP threshold setting
can be calculated according to equation 2.
V
IN
Table 6
SS
is the desired soft-start duration.
R
(see
2
=
F
R
(typically in the 100 pF-330 pF range) may be required to
LED7707
Section 5.3 on page 21
1
⋅
C
V
SS
OUT
SGND
≅
,
MAX
LX
I
OVSEL
SS
. 1
Figure 9
2
+
145
⋅
4 .
4
t
SS
V
V
−
. 1
).
Section 5.1.4
145
R
R
2
1
). After the SS voltage reaches a
V
C
F
V
C
OUT
OUT
), the floating rows are
LED7707
AM00586v1
AM00586v1