LED7707 STMicroelectronics, LED7707 Datasheet - Page 26

• Manufacturer Part Number: LED7707
• Description: LED Drivers 6-ROW 85mA LED DRIV BOOST REG LCD PANEL
• Manufacturer: STMicroelectronics

Specifications of LED7707

• High Level Output Current: 85 mA
• Operating Supply Voltage: 4.5 V to 36 V
• Maximum Supply Current: 1 mA
• Maximum Power Dissipation: 2.3 W
• Maximum Operating Temperature: + 150 C
• Mounting Style: SMD/SMT
• Package / Case: VFQFPN-24
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application information
26/47
Equation 13b
Where V
Note that, the lower the inductor value (and the higher the switching frequency), the higher
the bandwidth can be achieved. The output capacitor is directly involved in the loop of the
boost converter and must be large enough to avoid excessive output voltage drop in case of
a sudden line transition from the maximum to the minimum input voltages.
However a more significant requirement concerns the output voltage ripple.
The output capacitor should be chosen in accordance with the following expression:
Equation 14
where ΔV
inductor current, T
Section 6.4.4 on page 33
Once the output capacitor has been chosen, the R
Equation 15
Where GM = 2.7 S and g
Equation 15 places the loop bandwidth at f
place the frequency of the compensation zero 5 times lower than the loop bandwidth:
Equation 16
Where f
In most of the applications an experimental approach is also very valid to compensate the
circuit. A simple technique to optimize different applications is to choose C
and to replace R
transient response. Insufficient damping will result in excessive ringing at the output and
poor phase margin.
Figure 18
Z
IN,min
OUT, max
= f
(a and b) give an example of compensation adjustment for a typical application.
U
/5.
is the minimum input voltage and I
COMP
is the maximum acceptable output voltage ripple, I
OFF
is the off-time of the switching cycle (for an extensive explanation see
with a 10 kΩ trimmer adjusting its value to properly damp the output
).
EA
= 375 µS
C
OUT
C
R
COMP
COMP
>
(
I
R =
, L
=
=
peak
U
2
2
. Then, the C
G
⋅ π
Δ ⋅
V
I
2
OUT
M
OUT
−
⋅ π
V
f
Z
I
⋅
OUT
OUT
OUT
g
⋅
f
1
U
COMP
R
EA
,
⋅
COMP
max
)
is the overall output current.
C
⋅
⋅
T
M
OFF
can be calculated as:
COMP
capacitor is determined to
L, peak
COMP
is the peak
= 4.7 nF
LED7707