LED7706 STMicroelectronics, LED7706 Datasheet - Page 20

• 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
5.2.2
20/46
PWM dimming
The brightness control of the LEDs is performed by a pulse-width modulation of the rows
current. When a PWM signal is applied to the DIM pin, the current generators are turned on
and off mirroring the DIM pin behavior. Actually, the minimum dimming duty-cycle depends
on the dimming frequency.
The real limit to the PWM dimming is the minimum on-time that can be managed for the
current generators; this minimum on-time is approximately 500 ns.
Thus, the minimum dimming duty-cycle depends on the dimming frequency according to the
following formula:
Equation 11
For example, at a dimming frequency of 20 kHz, 1% of dimming duty-cycle can be
managed.
During the off-phase of the PWM signal the boost converter is paused and the current
generators are turned off. The output voltage can be considered almost constant because of
the relatively slow discharge of the output capacitor. During the start-up sequence (see
Section 5.1.3 on page 13
regardless of the applied dimming signal.
Figure 14. PWM dimming waveforms
) the dimming duty-cycle is forced to 100% to detect floating rows
D
DIM
,
min
=
500
ns
⋅
f
DIM
LED7706