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MC33288DDHR2

Solid State Relay for Automotive Flasher Applications

Freescale Semiconductor 

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

Power Supply

The MC33288 can be directly connected to the supply line.

In standby mode (IN1 and IN2 @ OV), the supply current is

less than 10 mA for VBAT supply voltage below 14 V. This

feature allows a very low supply current on the battery when

the car is idle or parked.

During the OFF state, the current recopy terminal and the

status terminals are in high impedance.

In case of loss of (digital) ground, the power MOSFETs

turn off in order to safely tie the load current to zero.

Nominal Voltage and Transient Operation

The nominal operation voltage is from 9.0 V to 16 V. The

MC33288 is functional over a larger voltage range from 8.0 V

to 35 V. The technology used for both power and analog

circuitry sustains 40 V DC voltage.

Reverse Battery

The MC33288 is self protected against reverse battery up

to -14 V in a continuous mode. When a negative battery

voltage arises, the MOSFETs are internally turned off. The

load current flows in the body diode of each MOSFET. The

power dissipation within the MC33288DH is then VF x ILOAD,

where ILOAD is the total current set by the loads and VF is the

forward body diode voltage. VF is 0.5 V typical at 150°C and

decreases with temperature with a drop of -2.0 mV/°C.

Power Output Switches

The device has two independent high-side switches. Each

switch is realized with an N-channel power MOSFET and

includes current and temperature sensing circuitries. The

MOSFET gates are driven by analog circuitry which includes

charge pump and fault detection. A specific feature of this

device is the output current recopy.

Each output has a 25 mΩ RDSON maximum at 25°C. The

RDSON value reaches 40 mΩ at 150°C junction temperature.

Each output has a parasitic drain to source diode, inherent to

the technology. This diode can sustain as much current as

the MOSFET. This diode is reversed biased during normal

operation of the MOSFET and is forward biased during

reverse battery or negative transient pulses.

The output MOSFET can each drive 8.0 A nominal. This

maximum current condition occurs when up to three 21 W

lamps and two small 5.0 W or 7.0 W lamps are connected on

each channel, at higher VBAT voltage specification. This is the

case when a trailor is attached to the car. As the flasher can

operate in warning or hazard operation mode with its two

channels on, the MC33288 can drive 16 A total.

When lamps are turned on, the inrush current can reach

up to 6 times the nominal lamp current. For this particular

application, the total inrush current can reach 6 x 8.0 A–that

is up to 48 A per channel. The 48 A value will only occur at

the first lamp turn-on. In order to optimise the total system

(MC33288, printed circuit board, wiring, fuse etc.), the device

incorporates a current limitation at 30 A typical. This means

that the first in rush current will be clamped at 30 A. The

second lamp turn-on of the flashing cycle will not see any

clamping as the lamps have been heated up in the previous

cycle.

IN1 and IN2 are the two inputs of the device, connected to

a microcontroller I/O; they are CMOS compatible. When

these inputs are in low state, the device is in standby mode.

When any of the inputs are switched to a high level, the

associated output MOSFET is turned on.

Status

The device has a single status terminal which reports an

overtemperature and an openload condition in the device.

This terminal is an open drain structure and needs an

external pull-up resistor. The device incorporates

overtemperature sense on each output MOSFET in order to

independently protect each output. But, the report of the

overtemperature is done through one single status terminal,

called STATUS, in order to minimize the number of I/O

connections of the MCU.

Open Load Function

The open load detection is active during the ON phase (hot

openload detection). An amplifier measures the differential

voltage between VBAT and VOUT.

When the load current is below 1.0 A, the openload

circuitry will pull down the status output. If the openload

condition is present before the device turn-on, the status will

be pulled down after a delay due to the rise time of the output.

Current Recopy Function

Flasher application needs to detect failed lamp. The

system must detect one 21 W lamp failing, in the flasher

application only, without a trailor. The MC33288 has an

output current recopy function which recopies on the CUR R

terminal a portion of the output current. Each channel is

connected to the same CUR R terminal as the system has to

operate in the flasher mode only and not in the warning

operation.

The MC33288 provides a current recopy of 1/1000 of the

main output current, either output left or right. The recopy

function has its higher accuracy of ±10% in the usual

operation range and an accuracy of ±20% in the total

operating range. This allows a precise detection of one 21 W

lamp, but also the detection of additional lamps in case of

trailor connection.

33288

8

Analog Integrated Circuit Device Data

Freescale Semiconductor

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