MC33198 Datasheet, PDF (7/11 Pages) Motorola, Inc – Automotive High Side TMOS Driver

MC33198
Freescale_DES_VICe_Em_DEi_Sc_Co_RIn_PTd_IOu_Nctor, Inc.
Introduction
The MC33198D is a high side TMOS driver, dedicated for
automotive applications. It is used in conjunction with an
external power MOSFET for high side drive applications. The
device can drive and protect a large variety of MOSFET. The
device has CMOS compatible input control, charge pump to
drive the MOSFET gate, fault detection circuitry based on
programmable Vds monitoring to detect shorted load. It also
includes a programmable timer function to eliminate
undesired switch off due to in rush currents and a status pin
which reports the output status in both on and off MOSFET
state. The device uses few external components and offers an
economical solution to large current high side switch. It also
has PWM capability up to 1kHz.
Power Supply
The MC33198D can be supplied from the battery line. It is
designed in a 60V technology, making it able to sustain up to
60V transient pulses. In off state, with pin 7 low, the supply
current is up to 5mA, and in operation, pin 7 high, the current
up to 25mA. The device has an undervoltage detection and
shutdown near 7V. Below this value the MOSFET is turned
off. There is also a 25V overvoltage detection which switches
off the output pin 4 to protect both MOSFET and load when
V_cc is higher than 25V.
Charge Pump
The device incorporates a self running charge pump with
internal capacitor and connected at Gate pin 4. To prevent
oscillation, a serial resistor can be added. The charge pump is
able to charge a 25nF capacitor in less than 1ms. This allows
the MC33198D to have a rapid response time and to drive the
external TMOS gate very quickly, allowing fast switching on of
the load. The device has an internal 14V zener diode between
pin 4 and 1 to clamp the Gate-to-Source voltage and protect
the MOSFET gate oxyde from destruction. See Dynamic
Electrical Characteristics table for details.
Band Gap and Reference Currents
The MC33198D has an internal band gap reference
voltage which generates all the internal thresholds. This band
gap is also used to generate internal reference currents
necessary for proper operation of the device.
These currents are :
Pin 2 : Drain current (typically 80µA).
Pin 4 : High and low gate discharge currents (typically
100µA and 10µA).
Pin 8 : Timer charge current (10µA typical).
All these currents are derivated from the same reference
voltage and internal resistor. Their accuracy and variability is
approximately +-25% over the full temperature and voltage
range. In addition, a passive pull down current of 5µA
maintains the gate of the MOSFET below 0.9V when the
device has no supply, ensuring that the MOSFETremains off.
This passive pulldown current is operating even if device V _cc
(pin 5) is not powered up.
Input Circuitry
The input of the device is CMOS compatible and can be
directly connected to a microcontroller. The input current is
determined by an internal pull down resistor of typically 36kΩ.
A hysteresis of 0.8 V minimum is present at this input.
Output Status
The device has a status output (pin 6) which has an open
collector structure. This pin is used to report the MOSFET
over load condition or the LOAD status when MOSFET is off.
The device Pin 1 (Source) is compared to a programmable
threshold at Pin 2, in both on and off state of the MOSFET.
This allows the detection of MOSFET over Vds or over load
conditions when MOSFET is on and load short to Vbat
monitoring when MOSFET is in off state. This status pin is
normally connected to a pull-up resistor and to a micro input
and can drive up to 1mA. See below for detailed operation.
Timer
The timer (pin 8) is used in conjunction with an external
capacitor to create a delay between the over load detection
and the shutdown of the MOSFET. In case of over load, the
internal current source pin 8 will charge the capacitor. When
the voltage at pin 8 reaches the 5.5V threshold, the internal
C3 comparator will be triggered and switch off the output to
protect the MOSFET. The fault and the MOSFET turn off
condition are latched and are reset by switching the input off
and on. The delay between over load detection and actual
MOSFET turn off is used to allow temporary over load wich
will prevent the system from switching off during possible in-
rush current or transients.
MOSFET Protection and Output Voltage Monitoring
The MC33198D has the ability to sense the output
MOSFET source voltage and compare it to a predetermined
threshold. This threshold is programmable using the internal
reference current of 80µA and an external resistor connected
at pin 2. The device can monitor the output load voltage, as
well as protect the MOSFET in case of over load.
The over load detection threshold must be adapted to the
MOSFET itself depending on the load to be driven and the
thermal capability of the MOSFET. In practice, the maximum
acceptable Vds of the MOSFET should be determined and
based upon MOSFET maximum power dissipation.
In addition, the pin 8 capacitor value should be calculated
to allow inrush current.
Source (Pin1) and Drain (Pin2) Functionality
These two pins are used to sense the MOSFET and load
conditions. Pin 2 is connected to the internal pull down current
source of 80µA and to the C2 comparator. An external resistor
connected between pin 2 and V_bat creates a voltage drop
across this resistor. The voltage drop will be the MOSFET
maximum acceptable drain to source voltage and the C2
comparator threshold.
For More Information On This Product,
MC33198
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