STEVAL-ILL021V1 STMicroelectronics, STEVAL-ILL021V1 Datasheet - Page 18

• 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
5.1.7
5.1.8
18/47
Boost current limit
The design of the external components, especially the inductor and the flywheel diode, must
be optimized in terms of size relying on the programmable peak current limit. The LED7707
improves the reliability of the final application giving the way to limit the maximum current
flowing into the critical components. A simple resistor connected between the BILIM pin and
ground sets the desired value. The voltage at the BILIM pin is internally fixed to 1.23 V and
the current limit is proportional to the current flowing through the setting resistor, according
to the following equation:
Equation 7
where
The maximum allowed current limit is 5 A, resulting in a minimum setting resistor
R
In a boost converter the RMS current through the internal MOSFET depends on both the
input and output voltages, according to equations 8a (DCM) and 8b (CCM).
The current limitation works by clamping the COMP pin voltage proportionally to R
Peak inductor current is limited to the above threshold decreased by the slope
compensation contribution.
Equation 8 a
Equation 8 b
Thermal protection
In order to avoid damage due to high junction temperature, a thermal shutdown protection is
implemented. When the junction temperature rises above 150 °C (typ.), the device turns off
both the control logic and the boost converter and holds the FAULT pin low. The LDO is kept
alive and normal operation is automatically resumed after the junction temperature has
been reduced by 30 °C.
BILIM
> 240 kΩ. The maximum guaranteed RMS current in the power switch is 2 A.
I
MOS
,
rms
=
I
OUT
⎛
⎜
⎜
⎝
(
1
I
I
MOS
BOOST
−
D
D
K
,
B
rms
)
2
,
=
PEAK
+
=
1.2 10
12
1
F
V
SW
IN
⎛
⎜
⎜
⎝
=
⋅
I
OUT
⋅
R
⋅
D
6
L
K
BILIM
V
V
B
OUT
⋅
f
D
3
SW
⋅
L
⎞
⎟
⎟
⎠
2
(
D
(
1
−
D
)
)
3
⎞
⎟
⎟
⎠
LED7707
BILIM
.