EVALED7706 STMicroelectronics, EVALED7706 Datasheet - Page 14

• Manufacturer Part Number: EVALED7706
• Description: EVALUATION BOARD FOR LED7706
• Manufacturer: STMicroelectronics

Specifications of EVALED7706

• Current - Output / Channel: 30mA
• Outputs And Type: 6, Non-Isolated
• Voltage - Output: 36 V
• Features: Dimmable, Extra 5V Output
• Voltage - Input: 4.5 ~ 36 V
• Utilized Ic / Part: LED7706
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6445

Operation description
5.1.4
14/46
selector (see
reacts by increasing the output voltage. When it reaches the floating row detection (FRD)
threshold (95% of the OVP threshold), the floating rows are managed according to
(see
finishes and all the protections turn active. The soft-start capacitor C
according to equation 2.
Equation 2
Where I
Overvoltage 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 1.234 V threshold. When the voltage on the OVSEL pin exceeds the OV threshold,
the FAULT pin is tied low and the device is turned off; this condition is latched and the
LED7706 is restarted by togglin g the EN pin or by performing a Power-On Reset (the POR
occurs when the LDO output falls below the lower UVLO threshold and subsequently
crosses the upper UVLO threshold during the rising phase of the input voltage). Normally,
the value of the high-side resistors of the divider must be chosen as high as possible (but
lower than 1 M Ω ) to reduce the output capacitor discharge when the boost converter is off
(during the off phase of the dimming cycle). The R2/R1 ratio is calculated to trigger the OVP
circuitry as soon as the output voltage is 2 V higher than the maximum value for a given LED
string (see equation 3). Two additional filtering capacitors, C
improve noise rejection at the OVSEL pin, as shown in
in the 100 pF-330 pF range, while the C
Equation 3
Equation 4
Section 5.3 on page 21
SS
= 5 µA and t
Figure 5
). As a consequence the error amplifier is unbalanced and the loop
SS
is the desired soft-start duration.
). After the SS voltage reaches a 2.4 V threshold, the start-up
R
2
=
R
1
⋅
C
V (
C
13
13
SS
OUT
=
value is given by equation 4.
≅
,
OVP
2
I
⋅
SS
C
. 1
2
+
10
234
⋅
4 .
t
2
SS
R
R
V
V
2
1
−
. 1
Figure 9
234
10
) V
and C
. The typical value for C
SS
13,
can be calculated
may be required to
LED7706
Table 6
10
is