LED7706 STMicroelectronics, LED7706 Datasheet - Page 12

• Manufacturer Part Number: LED7706
• Description: IC LED DRIVR WHT BCKLT 24-VFQFPN
• Manufacturer: STMicroelectronics
• Type: Backlight, White LEDr

Specifications of LED7706

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 250kHz ~ 1MHz
• Voltage - Supply: 4.5 V ~ 36 V
• Voltage - Output: 36V
• Mounting Type: Surface Mount
• Package / Case: 24-VFQFN, 24-VFQFPN
• Current - Output / Channel: 30mA
• Internal Switch(s): Yes
• Operating Supply Voltage: 4.5 V to 36 V
• Maximum Supply Current: 1 mA
• Maximum Power Dissipation: 2300 mW
• Maximum Operating Temperature: + 150 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• For Use With: 497-10043 - BOARD EVAL LCD BACKLIGHT LED7706497-8360 - BOARD EVAL FOR LED7707497-6445 - EVALUATION BOARD FOR LED7706
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Operating Temperature: -
• Efficiency: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Operation description
5.1.2
12/46
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