SC654 Datasheet, PDF (12/22 Pages) Semtech Corporation – Light Management Unit for 6 LEDs with SemPulseTM Interface

SC654
Applications Information (continued)
ration is being used. Note that it is only necessary to set
the BLEN bits for the main display.
Table 1 — Fade-In from Off State
Command
Sequence
Action
Data
1. Disable fade
Write to register 04h
00h
2. Set Main back-
lights to 0.5mA
3. Enable fade
Write to register 01h
Write to register 04h
04h
01h, 02h, or 03h
(but not 00h)
4. Set BLEN bits
Write to register 00h
any value 01h
through 3Fh
(but not 00h)
5. Set new value of
Write to register 01h
backlight current
any value 05h
through 1Fh
Fade-Out from any On State to Off State
Fading the backlight LEDs from any active state to the off
state follows a simple procedure. The sequence of com-
mands for this action is shown in Table 2. Following these
steps explicitly will ensure that the fade-out operation will
proceed with no interruption at the rate specified in the
Main Fade register (04h). This procedure must be followed
regardless of the backlight grouping configuration.
Table 2 — Fade-Out from any On State to Off State
Command
Sequence
1. Enable fade
2. Set Main back-
lights to 0mA
Action
Write to register 04h
Write to register 01h
Data
01h, 02h, or 03h
(but not 00h)
00h
Fading Between Different On States
Fading from one backlight level to another (up or down)
also follows a simple procedure. The sequence of com-
mands for this action is shown in Table 3. Following these
steps explicitly will ensure that the fade-in/fade-out oper-
ation will proceed with no interruption at the rate specified
in the Main Fade register (04h). This procedure must be
followed regardless of the backlight grouping
configuration.
Table 3 — Fading between Different On States
Command
Sequence
Action
Data
1. Enable fade
Write to register 04h
01h, 02h, or 03h
(but not 00h)
2. Set new value of
Write to register 01h
backlight current
Any value 05h
through 1Fh
Additional Information
For more details about the Fade-in/Fade-out function,
refer to the SC654 Backlight Driver Software User’s Guide
and SemPulse Interface Specification document and to the
associated software drivers available for this device
(contact your sales office for more details).
Shutdown Mode
The device is disabled when the SPIF pin is held low for
the shutdown time specified in the electrical characteris-
tics section. All registers are reset to default condition at
shutdown.
Sleep Mode
When all LEDs are disabled, sleep mode is activated. This
is a reduced current mode that helps minimize overall
current consumption by disabling the clock and the
charge pump while continuing to monitor the serial inter-
face for commands. An additional current savings can be
obtained by putting the serial interface in standby mode
(see SemPulse Interface, Standby Mode).
Protection Features
The SC654 provides several protection features to safe-
guard the device from catastrophic failures. These features
include:
• Output Open Circuit Protection
• Over-Temperature Protection
• Charge Pump Output Current Limit
• LED Float Detection
Output Open Circuit Protection
Over-Voltage Protection (OVP) at the OUT pin prevents
the charge pump from producing an excessively high
output voltage. In the event of an open circuit between
the OUT pin and all current sinks (no loads connected),
the charge pump runs in open loop and the voltage rises
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