MC34844EP Datasheet, PDF (44/62 Pages) Freescale Semiconductor, Inc – 10 Channel LED Backlight Driver with Integrated Power Supply

FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
MC34844A
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
MC34844 - Functional Block Diagram
Regulators / Power Down
3 Internal Regulators
Protection / Failure Detection
Over-temperature Protection
Over-current Protection
Under-voltage Protection
Over-voltage Protection
LED Open Protection
Logic Control
Optical and Temperature Control
Boost
LED Channels
PWM Dimming
Serial Interface Control
Regulator / Power down Protection / Failure Detection
Logic Control LED Channels Boost
Figure 25. Functional Internal Block Diagram
REGULATORS
The 34844A is designed to operate from input voltages in
the 7.0 to 28 V range. This is stepped down internally by
LDOs to 2.5 V (VDC1 and VDC3) and 6 V (VDC3) for
powering internal circuitry. If the input voltage falls below the
UVLO threshold, the device automatically enters in shut
down mode.
Power UP Sequence:
The power up sequence for applying V_IN, with respect to
the ENABLE and PWM signals, is very important to assure a
good performance of the part.
It is recommended to follow this sequence:
1. Apply V_IN first
2. Wait for a couple of milliseconds (~2.0 ms) to let the
logic and internal regulators get settled
3. Take the EN pin high, or keep it low depending on the
operating mode
4. Apply the PWM signal
Operating Modes:
The device can be operated by the EN pin and/or SDA/
SCK bus lines, resulting in three distinct operation modes:
• Manual mode, there is no I²C capability, the bus line pins
must be tied low, and the EN pin controls the ON/OFF
operation. To shutdown the part in Manual mode, first the
PWM pin should be taken low followed by the EN pin. The
part will not shut down unless V_OUT collapses to a voltage
below 30 V.
• SM Bus mode, EN pin must be tied low and the device is
turned ON by any activity on the bus lines. The part shuts
down if the bus lines are held low for more than 30 ms, the
30 ms watchdog timer can be disabled by I²C (setting
SETI2C bit high) or tying the EN pin high. In Sleep mode
(EN bit=0) the device reduces the power consumption by
leaving “alive” only the blocks required for I²C
communication.To shutdown the part in SM Bus mode, the
EN bit should first be a '0', then the SCK and SDA should
be taken low.
• I²C mode, has to be configured by I²C communication
(SETI2C bit = 1) right after the IC is turned ON, it prevents
the part from being turned ON/OFF by the bus. Sleep
mode is also present and it is intended to save power, but
still keep the IC prepared to communicate by I²C. By
taking the EN bit low and then the EN pin low, the part
enters into a shutdown mode.
34844A
44
Analog Integrated Circuit Device Data
Freescale Semiconductor