MC33286 Datasheet, PDF (5/8 Pages) Motorola, Inc – Automotive Dual

Freescale Semiconductor, Inc.
MC33286
General Information
FUNCTIONAL DESCRIPTION
Input Trigger
This device is a dual high side power switch dedicated for
The MC33286 has a special input trigger circuitry allowing
automotive applications. In comparison with mechanical the device to have less than 0.5µA typical standby current.
relays, this device offers higher reliability as well as protection When the input level is below 1.5V, the circuit is in sleep mode
and diagnostic features. It has been designed to be directly (see Figure 4).
connected to the battery voltage.
In the future, the number of electronic switches directly Status Output
connected to the battery will increase, so the MC33286
The output status is an open drain structure, active at low
includes a special input trigger and architecture which allows level, so an external pull-up resistor is required to read the
to have a very low standby current when the V_bat is lower than
12V.
status information.
The status indicates the open load and the over
The MC33286 concept uses a dual chip approach packaged temperature information. The output short-circuit, current
in a single SO20 package. This low power package can be used
because the ON resistance of the switch (35mΩ max at 25°C)
limitation and V_bat undervoltage are not reported on the status
pin. But an output short-circuit to Gnd will be detected by an
guarantees a low power dissipation (less than 300mW) when overtemperature because the total power dissipation of the
driving two 21Watts lamps. The two chips are internally connected device will make it reach the thermal detection.
by die to die wire bonding to allow the transfer of analog and
control information between the two dice.
Open Load Function
The two chips are the Control and Power dice.
The open load detection is active during the ON phase (Hot
The Control chip uses the SMARTMOS3.5NVM open load detection). An amplifier measures the differential volt-
technology. The two channels of this control chip are totally
symmetrical and independant. It drives the gate of the output
age between V_bat and V_out (this value is typically 400mA) at
25°C.
power MOSFET and manages the analog information from the
An open load condition will create a voltage lower than 12mV
power MOSFET die to ensure power device protection.
and the open load circuitry will detect it and will pull down the sta-
The Power chip uses the HDTMOS3 technology. It has tus output. If the open load condition is present before the device
one independent sources plus current sensing cells for open turn-on, the status will be pulled down after a delay due to the rise
load detection and current limitation. In addition, a thermal time of the output.
sensor (diode) is located in the middle of each source to
protect the MC33286 against overtemperature. The drain of Overcurrent Function (High Current Limitation)
the Power die is connected to the battery voltage by the lead
The device incorporates a current limitation at 30 Amps
frame of the package. This lead frame has been especially typical when outputs are loaded (Vout > 1V) . A 21 Watts lamp
developed and has eight pins connected together to the V_bat.
These pins are used as the V_bat connection as well as thermal
path.
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
Supply Voltage
activated during the inrush current of one lamp but will protect
The MC33286 can be directly connected to the V_bat line.
Figure 4 shows the supply voltage characteristics. The V_batc
(V_bat of Control die, pin 10) and V_bat (V_bat of power die, pins 1,
2, 5, 6, 15, 16, 19, 20) are not internally connected, so the V_bat
and V_batc have to be connected externally by the printed
circuit board.
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
Under Voltage
switch the device off. Nevertheless the peak power
Figure 4 also shows the supply voltage characteristic dissipation and energy is quite high.
when one or two sides of the MC33286 are turned on. From
Therefore, a short circuit protection has been
0V to undervoltage level (7V typical), all blocks of the implemented and is activated when the output voltage is lower
MC33286 are not totally supplied. The undervoltage threshold than about 1V . As shown in the Figure 5, the low current
value versus temperature is shown in Figure 2.The under limitation decreases with temperature. In the case of a short
voltage function allows the turn-off of the output transistor, circuit, the power dissipated in the device decreases with time
because the V_bat voltage will be not enough to guarantee the
full on state of the output transistor due to an incomplete drive
due to the decay of the current limitation with temperature.
of the gate. When the V_bat is greater than the undervoltage
threshold, the supply current increases due to the charge
Overtemperature Function
The overtemperature function uses a thermal sensor
pump start up and MOSFET driver activation.
located in the middle of each output power HDTMOS
Reverse Battery Protection
transistor. The sensor is a diode connected to V_bat in the
power die. The diode forward voltage varies of -2mV/°C. So,
When a negative battery voltage arises, the current flows by measuring the diode voltage the power output MOSFET
in a reverse direction from the source region to drain region of temperature is monitored. This diode voltage information is
both of the MosFets through the body diode. The limitation is transferred to the control die and compared to a reference
then the temperature reached by the junction, which is linked voltage generated from the band gap reference generator.
to the thermal impedance from the junction to the ambiant.
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
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