MC33286

FUNCTIONAL DESCRIPTION

Automotive Dual High Side Driver

5

General Information

This device is a dual high side power switch dedicated for

automotive applications. In comparison with mechanical

relays, this device offers higher reliability as well as protection

and diagnostic features. It has been designed to be directly

connected to the battery voltage.

In the future, the number of electronic switches directly

connected to the battery will increase, so the MC33286

includes a special input trigger and architecture which allows

12V.

The MC33286 concept uses a dual chip approach packaged

in a single SO20 package. This low power package can be used

because the ON resistance of the switch (35m

Ω max at 25°C)

guarantees a low power dissipation (less than 300mW) when

driving two 21Watts lamps. The two chips are internally connected

by die to die wire bonding to allow the transfer of analog and

control information between the two dice.

The two chips are the Control and Power dice.

The

Control

chip

uses

the

SMARTMOS3.5NVM

technology. The two channels of this control chip are totally

symmetrical and independant. It drives the gate of the output

power MOSFET and manages the analog information from the

power MOSFET die to ensure power device protection.

The Power chip uses the HDTMOS3 technology. It has

one independent sources plus current sensing cells for open

load detection and current limitation. In addition, a thermal

sensor (diode) is located in the middle of each source to

protect the MC33286 against overtemperature. The drain of

the Power die is connected to the battery voltage by the lead

frame of the package. This lead frame has been especially

path.

Supply Voltage

circuit board.

Under Voltage

Figure 4 also shows the supply voltage characteristic

when one or two sides of the MC33286 are turned on. From

0V to undervoltage level (7V typical), all blocks of the

MC33286 are not totally supplied. The undervoltage threshold

value versus temperature is shown in Figure 2.The under

voltage function allows the turn-off of the output transistor,

full on state of the output transistor due to an incomplete drive

threshold, the supply current increases due to the charge

pump start up and MOSFET driver activation.

Reverse Battery Protection

When a negative battery voltage arises, the current flows

in a reverse direction from the source region to drain region of

both of the MosFets through the body diode. The limitation is

then the temperature reached by the junction, which is linked

to the thermal impedance from the junction to the ambiant.

Input Trigger

The MC33286 has a special input trigger circuitry allowing

the device to have less than 0.5µA typical standby current.

When the input level is below 1.5V, the circuit is in sleep mode

(see Figure 4).

Status Output

The output status is an open drain structure, active at low

level, so an external pull-up resistor is required to read the

status information.

The status indicates the open load and the over

temperature information. The output short-circuit, current

pin. But an output short-circuit to Gnd will be detected by an

overtemperature because the total power dissipation of the

device will make it reach the thermal detection.

Open Load Function

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

open load detection). An amplifier measures the differential volt-

25°C.

An open load condition will create a voltage lower than 12mV

and the open load circuitry will detect it and will pull down the sta-

tus output. If the open load 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.

Overcurrent Function (High Current Limitation)

The device incorporates a current limitation at 30 Amps

typical when outputs are loaded (Vout > 1V) . A 21 Watts lamp

has a nominal current of about 2 amp and at turn on, the

MC33286 has to drive a peak current of about 12A, as the

lamp inrush current is about six times the nominal DC current.

A standard current limitation set up at 30A will not being

activated during the inrush current of one lamp but will protect

the circuit against overcurrent. Figure 3 shows the overcurrent

threshold versus temperature.

Short Circuit Protection (Low Current Limitation)

During a hard short-circuit to Gnd, the power dissipation

would be 30A x 14V = 420 Watts if only the overcurrent

limitation exists. The thermal protection will be activated and

switch

the device

off. Nevertheless the peak power

dissipation and energy is quite high.

Therefore,

a

short

circuit

protection

has

been

implemented and is activated when the output voltage is lower

than about 1V . As shown in the Figure 5, the low current

limitation decreases with temperature. In the case of a short

circuit, the power dissipated in the device decreases with time

due to the decay of the current limitation with temperature.

Overtemperature Function

The overtemperature function uses a thermal sensor

located in the middle of each output power HDTMOS

power die. The diode forward voltage varies of -2mV/°C. So,

by measuring the diode voltage the power output MOSFET

temperature is monitored. This diode voltage information is

transferred to the control die and compared to a reference

voltage generated from the band gap reference generator.

When the temperature reaches the overtemp threshold, the

circuit is turned off. As the input voltage is still high, the circuit

is not in wake mode but the current consumption decreases

due to the turn-off of the charge pump. The overtemperature

Freescale Semiconductor, Inc.

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