mc33091ap Freescale Semiconductor, Inc, mc33091ap Datasheet - Page 9

• Manufacturer Part Number: mc33091ap
• Description: High-side Tmos Driver
• Manufacturer: Freescale Semiconductor, Inc

Introduction
N–channel TMOS transistors in high–side configured, low
frequency switching applications. The MC33091A has an
internal charge pump to fully enhance the on–state of the
TMOS device. The MC33091A protects the TMOS device
from shorts to ground and provides a Fault output to report
the presence of an overcurrent condition. The few additional
external components required allow tailoring of the
application’s protection level. The protection scheme of the
MC33091A uses an externally programmable, nonlinear
timer that disables the TMOS device in the event the drain to
source voltage exceeds a specified value for a specified
duration. Both the value and duration are externally
programmable allowing for flexibility in applications.
Description of Pins
functional blocks of the MC33091A. The discussion to follow
references this figure.
with CMOS logic families. The Input enables the protection
and charge pump circuitry. With the Input in a logic low state
the MC33091A draws only leakage current of less than
300
will be in the “off” state. When the Input is in a logic high state,
the Gate voltage (Pin 4) rise is limited to a maximum of 14 V
above SRC (Pin 1), due to an internal clamp diode being
used and the TMOS device is enhanced full on.
collector NPN transistor capable of sinking at least 500 A
when the TMOS gate is disabled due to an overcurrent
condition. When the TMOS device experiences an
overcurrent condition, the Fault pin is pulled low.
voltage and is the input to the V DS buffer used in conjunction
with the DRN pin in monitoring the drain to source voltage
developed across the TMOS device. The purpose of the
1.0 k resistor connected to this pin is to protect the SRC input
from overvoltage as a result of flyback voltage produced
when the TMOS device is used to switch large inductive
loads. This resistor can be eliminated when switching
noninductive loads.
pin and together constitute a V DS monitor of the TMOS drain
to source voltage. Feedback from the SRC pin will maintain a
voltage across the resistor, R X , equal to the V DS voltage
developed across the TMOS device. The series resistor, R X ,
connected between the drain of the TMOS device and DRN
of the MC33091A is used in conjunction with the feedback
buffer and associated PNP transistor to establish a current
proportional to the drain to source voltage, V DS , of the TMOS
device. This proportional current, acted upon by the current
squaring circuit of the MC33091A, is an important part of the
TMOS protection scheme.
MC33091A. An internal 30 V zener clamp connected to this
MOTOROLA ANALOG IC DEVICE DATA
The MC33091A is designed to drive a wide variety of
Figure 1 shows a typical application as well as the internal
Input (Pin 7): The logic levels of the Input are compatible
Fault (Pin 6): The Fault output is comprised of an open
SRC (Pin 1): The SRC pin senses the TMOS source
DRN (Pin 2): The DRN is used in conjunction with the SRC
V CC (Pin 5): The V CC pin supplies operational power to the
A and in this condition the associated TMOS device
FUNCTIONAL DESCRIPTION
MC33091A
pin provides overvoltage protection of the MC33091A. When
the zener is activated, the MC33091A disables the TMOS
device only for the duration of the overvoltage but the Fault
output (Pin 6) does not change logic states. The Fault pin
does not go to a logic low state during the overvoltage
duration since this is not an MC33091A device fault, but an
external system fault.
of the internal charge pump which controls the TMOS device.
The charge pump is a voltage tripler and requires no
additional external components for operation. When the Input
is at a logic low state, the charge pump will be turned off.
When the Input is pulled to a logic high state, with no load
fault existing, the charge pump turns on and pumps the
TMOS gate voltage to at least 8.0 V, typically 10 to 14 V,
above V CC . An internal zener clamp is incorporated to limit
the Gate to approximately 14 V above the source and
prevent rupture of the TMOS gate.
window comparators and an output of the current squaring
circuit. An external resistor (R T ) and capacitor (C T ) are tied to
this node so as to afford programing the characteristics
necessary for protection of the TMOS device.
Overcurrent Protection Timer
of the MC33091A to constantly sense the voltage drop
developed across the TMOS device. A low voltage drop is
indicative of normal TMOS “on” operation while a large
voltage drop represents the existence of an overcurrent
condition. By monitoring the TMOS drain to source voltage
(V DS ) the MC33091A is able to detect a shorted load and
react to disable the TMOS device. The circuit protection
scheme is essentially based on a timer whose rate is
dependent on the magnitude of V DS . If the drain to source
voltage is large (i.e. V DS = V CC ), the timer will disable the gate
drive very quickly. If V DS is only slightly above the normal
operating level, the timer will take much longer to disable the
gate drive.
proportional to V DS 2 , low V DS conditions can be tolerated for
a longer time than high V DS conditions. To enhance the
system application, the timer time–out of the MC33091A is
inversely proportional to V DS 2 . This approach maximizes the
TMOS operating range. The timer parameters are completely
user programmable through the use of external components
affording application usage of a wide variety of TMOS
devices. This is intended to model the generation and
dissipation of heat within the TMOS device.
timer characteristics. Once enabled, the MC33091A will
source a current, I SQ , from the timer pin that is proportional to
V DS 2 such that:
Gate (Pin 4): The Gate pin of the MC33091A is the output
V T (Pin 8): The Timer pin (V T ) is both an input to the timer
The MC33091A protection scheme is based on the ability
Since the power dissipated in the TMOS device is
The external components R X , R T and C T determine the
where: K =
I SQ =
KV DS 2
1/(R X 2 I Q )
(1)
9