LED7708 STMicroelectronics, LED7708 Datasheet - Page 20

• Manufacturer Part Number: LED7708
• Description: LED Lighting Drivers 16 Ch 85mA LED 3.6 to 36V 250kHz
• Manufacturer: STMicroelectronics

Specifications of LED7708

• Rohs: yes

Recommended operating conditions
8.1
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Device power-up and soft-start
The VSI pin (supply input for the serial interface) has a high level threshold lower than the
upper UVLO threshold at the LDO3 pin, ensuring that the serial interface is enabled prior to
the device being turned on. Anyway, after the POR, the DEN (device enable) bit of the
internal DEVCFG0 control register is low (default value) and the device is off. The soft-start
sequence takes place as soon as this bit is asserted.
If the LED7708 is set to operate in standalone, the soft-start procedure takes place in two
steps
1.
2.
Figure 4.
A slightly different soft-start procedure takes place if the LED7708 is set to operate as
master in conjunction with other slave devices:
1.
2.
3.
4.
The switching frequency is reduced to one fourth of the nominal value and the boost
current limit is set to 20%. This phase finishes approximately 1 ms after the output
voltage reaches the maximum value (not the OVP level). During this phase the
channels are disabled.
Both the switching frequency and the boost current limit are released to their respective
nominal values and then the channels are enabled.
The switching frequency is reduced to one eighth of the nominal value and the boost
current limit is set to 20%. This phase finishes approximately 1 ms after the output
voltage reaches the maximum value (not the OVP level). During this phase the
channels are active.
The switching frequency is increased to half the nominal value. This phase is held for
approximately 2 ms.
The switching frequency is further increased to the nominal value while the current limit
changes to 40% (~5 ms duration).
The current limit is released to its nominal values.
(Figure
Soft-start waveforms (standalone operation)
4):
Doc ID 022698 Rev 1
LED7708