Functional description

L9848

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Functional description

3.1

General features

The L9848 IC is a monolithic integrated circuit, which provides high flexibility for driving

medium loads. 8 outputs, whereof 6 (Output1-6) can be used as either internal low or high

side drives in any combination and 2 are dedicated low side outputs (Output7-8). The use of

this device reduces the I/O port requirements of the microprocessor by having serially

controlled outputs via a SPI interface. In addition, Output5-6 are capable of being PWMed

via an external pin (Input5-6). The 8bit SPI input is used to command the 8 output drivers

either ON or OFF and additional to indicate latched fault conditions that may have occurred.

Multiple L9848s may be daisy-chained with one additional microprocessor I/O port (CSn) for

each device. The implemented self-configuration allows the user to connect a high or low

side load to any of these outputs and the L9848 will drive them correctly as well as provide

proper fault mode operation with no other needed inputs. This device switch variable load

currents within the operation temperature range. The outputs are MOSFET drivers to

minimize Vdd current requirements. There's no VBatt input pin however VBatt is connected to

the drains of high side outputs.

The L9848 meets all required specifications when the supply voltage applied to the drain(s)

of the outputs is within the operating range. For supply voltages applied to the drain(s) down

to 6.8V the part is functional however, it does not meet all parametric limits, i.e. output on-

state voltages.

3.2

Outputs - Common characteristics

The 6 self-configuring outputs (Outputs1-6) are able to drive either incandescent lamps,

inductive loads (non-PWMed), or resistive loads biased to VBatt. These outputs are enabled

and disabled via the SPI bus. Each of these outputs is short circuit current limited and has

an over-temperature protection as described under "Functional Description - Thermal

Shutdown".

When a high side configured output is commanded OFF after having been commanded ON,

the source voltage will go to the lesser negative of (VBatt-45V). This is due to the design of

the circuitry and the transconductance of the MOSFET.

When a low side configured output is commanded OFF after having been commanded ON,

the output voltage will rise to the internal zener clamp voltage (40 Vdc minimum) due to the

flyback of the inductive load.

3.2.1

Output 1-4

These four outputs can be used as either high or low side drives. Integrated current source

pull-ups and pull-downs are employed to correctly latch "open load" fault data. Both of these

current sources are needed to detect an open load state since these outputs self configure

as either high or low side drives.

Drain connections of output1-4 (DRN1-4)

These pins are connected to the drains of the n-channel MOSFET transistors.

Source connections of output1-4 (SRC1-4)

These pins are connected to the sources of the n-channel MOSFET transistors.