Analog Integrated Circuit Device Data



Freescale Semiconductor

15

34844

FUNCTIONAL DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

Figure 5. Functional Internal Block Diagram

REGULATORS

The 34844 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 shutdown mode.

Power UP Sequence:

The power up sequence for applying VIN, 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 VIN 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 shutdown unless VOUT

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.

MC34844 - Functional Block Diagram

Regulator / Power down

Protection / Failure Detection

LED Channels

LED Channels

Logic Control

Regulators / Power Down

Three Internal Regulators

Protection / Failure Detection

Logic Control

Serial Interface Control

Boost

Boost

Optical and Temperature Control

PWM Dimming

Overtemperature Protection

LED Open Protection

Overcurrent Protection

Undervoltage Protection

Overvoltage Protection