EVALED7706 STMicroelectronics, EVALED7706 Datasheet - Page 12

• 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
5.1.2
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A dedicated circuit automatically selects the lowest voltage drop among all the rows and
provides this voltage to the main loop that, in turn, regulates the output voltage. In fact, once
the reference generator has been detected, the error amplifier compares its voltage drop to
the internal reference voltage and varies the COMP output. The voltage at the COMP pin
determines the inductor peak current at each switching cycle. The output voltage of the
boost regulator is thus determined by the total forward voltage of the LEDs strings (see
Figure
Equation 1
where the first term represents the highest total forward voltage drop over N active rows and
the second is the voltage drop across the leading generator (400 mV typ.).
The device continues to monitor the voltage drop across all the rows and automatically
switches to the current generator having the lowest voltage drop.
Figure 6.
Enable function
The LED7706 is enabled by the EN pin. This pin is active high and, when forced to SGND,
the device is turned off. This pin is connected to a permanently active 2.5 μA current source;
when sudden device turn-on at power-up is required, this pin must be left floating or
connected to a delay capacitor. When turned off, the LED7706 quickly discharges the
soft-start capacitor and turns off the power MOSFET, the current generators and the LDO.
The power consumption is thus reduced to 20 μA only.
In applications where the dimming signal is used to turn on and off the device, the EN pin
can be connected to the DIM pin as shown in
6):
Calculation of the output voltage of the boost regulator
V
IN
generators
controller
Current
section
Boost
V
OUT
=
N
max
ROWS
i
=
1
(
m
Row with the highest voltage
Σ
LEDS
j
=
1
Figure
drop across LEDs
V
F
j ,
)
+
7.
400
I
LED
generator
400 mV
mV
Leading
max
Σ
V
F
V
BOOST
LED7706
AM00599v1
8 1