PC33879EKSLASHR2 datasheet(17/20 Pages) MOTOROLA

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MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

33879

An output OFF open load fault is indicated when the drain-to-

source voltage is less than the output threshold voltage

(VOUT(flt-th)) of 2.5 V to 4.0 V. Hence, the 33879 will declare the

load open in the OFF state when the output drain-to-source

voltage is less than VOUT(flt-th).

This device has an internal 80

µA current source connected

from drain to source of the output MOSFET. The current source

may be programmed on or off via SPI. The Power-ON Reset

state for the current source is “off” and must be enabled via SPI.

To achieve low sleep mode quiescent currents, the Open Load

Detection Current source of each driver is switched off when

VDD or EN is removed.

During output switching, especially with capacitive loads, a

false output OFF open load fault may be triggered. To prevent

this false fault from being reported, an internal fault filter of

100

µs to 300 µs is incorporated. A false fault reporting is a

function of the load impedance, RDS(ON), COUT of the MOSFET,

as well as the supply voltage, VPWR. The rising edge of CS

triggers the built-in fault delay timer. The timer will time out

before the fault comparator is enabled and the fault is detected.

Once the condition causing the open load fault is removed, the

device will resume normal operation. The open load fault,

however, will be latched in the output DO register for the MCU

to read.

Shorted Load Fault

A shorted load (overcurrent) fault can be caused by any

output being shorted directly to supply, or an output

experiencing a current greater than the current limit.

There are two safety circuits progressively in operation

during load short conditions that provide system protection:

1. The device’s output current is monitored in an analog

fashion using SENSEFET approach and current limited.

2. The device’s output thermal limit is sensed and when

attained causes only the specific faulted output to shut

down. The output will remain off until cooled. The device

will then reassert the output automatically. The cycle will

continue until fault is removed or the command bit

instructs the output off. Shorted load faults will be

reported properly through SPI regardless of Open Load

Detection Current enable bits.

Undervoltage Shutdown

An undervoltage condition on VDD or VPWR will result in the

shutdown of all outputs. The VDD undervoltage threshold is

between 0.8 V and 3.0 V. VPWR undervoltage threshold is

between 3.0 V and 5.0 V. When the supplies fall below their

respective thresholds, all outputs are turned OFF. As both

supplies returns to normal levels, internal logic is reset and the

device resumes normal operation.

Output Voltage Clamp

Each output of the 33879 incorporates an internal voltage

clamp to provide fast turn-off and transient protection of each

output. Each clamp independently limits the drain-to-source

voltage to 45 V for low-side drive configurations and -20 V for

high-side drive configurations. The total energy clamped (EJ)

can be calculated by multiplying the current area under the

current curve (IA) times the clamp voltage (VCL) (see

Figure 16).

Characterization of the output clamps, using a single pulse

non-repetitive method at 0.35 A, indicates the maximum energy

per output to be 50 mJ at 150°C junction temperature.

Figure 16. Output Voltage Clamping

SPI Configurations

The SPI configuration on the 33879 device is consistent with

other devices in the Octal Serial Switch (OSS) family. This

device may be used in serial SPI or parallel SPI with the 33298

and 33291. Different SPI configurations may be provided. For

more information, contact Motorola Analog Products Division or

local Motorola representative.

Reverse Battery

The 33879 has been designed with reverse battery

protection on the VPWR pin.

All outputs consist of a power MOSFET with an integral

substrate diode. During the reverse battery condition, current

will flow through the load via the substrate diode. Under this

circumstance, relays may energize and lamps will turn on.

Where load reverse battery protection is desired, a reverse

battery blocking diode must be placed in series with the load.

Current

Area (IA)

Clamp Energy

(EJ = IA x VCL)

Clamp Energy

(EJ = IA x VCL)

Drain Voltage

Source Voltage

Time

BAT

Drain-to-Source Clamp

Voltage (VCL = 45 V)

Drain Current

(ID = 0.3 A)

GND

Drain-to-Source ON

Voltage (VDS(ON))

Drain-to-Source ON

Voltage (VDS(ON))

Current

Area (IA)

Source Current

(IS = 0.3 A)

Source Clamp Voltage

(VCL = -15 V)

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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