SA56 Apex Microtechnology, SA56 Datasheet - Page 7

• Manufacturer Part Number: SA56
• Description: PULSE WIDTH MODULATION AMPLIFIER
• Manufacturer: Apex Microtechnology

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OPERATING
CONSIDERATIONS
4 QUADRANT DIGITAL MODE
includes magnitude and direction information. The digital PWM
input signal is applied to the DIR pin, as shown in Figure 4,
and the PWM pin is tied HIGH to V
MOSFETs will switch in a locked, complementary fashion.
A
average differential voltage over each period applied to the
load will therefore be zero.
through zero current for low-speed applications. However,
power dissipation is slightly higher than in two-quadrant opera-
tion since all four output MOSFETs must switch every cycle.
BRAkING – DIGITAL MODE
motor by shunting the winding currents through the output
MOSFETs. Logic LOW on the PWM input both A and B out-
puts high. The motor winding current circulates through the on
resistance of the MOSFETs quickly slowing the motor.
during the braking of the motor. However, the current during
braking circulates in the normal forward direction through one
output MOSFET and is in the reverse in the other MOSFET.
The current sense feature can measure only forward currents.
The logic input on the DIR pin dictates which output MOSFET
is used for sensing the forward current during braking.
PROTECTION CIRCUITS
hard-wired ("screwdriver") short from an output to ground.
While the short-circuit protection will latch the output MOSFETs
within 500 ns (typical), the die and package may be required to
dissipate up to 500 Watts of power until the protection circuits
are activated.
ing voltages, so sound thermal design is critical if fault tolerance
is to be established in the design. The V
become very hot during this period of high current.
SA56 to prevent damage in the event that faults occur as
described below:
APEX MICROTECHNOLOGY CORPORATION • TELEPHONE [phone] • FAX [phone] • ORDERS [phone] • EMAIL [e-mail]
This data sheet has been carefully checked and is believed to be reliable, however, no responsibility is assumed for possible inaccuracies or omissions. All specifications are subject to change without notice.
OUT
During four-quadrant operation a single digital PWM input
Under digital control, the SA56 can rapidly decelerate the
The most severe condition for any power device is a direct,
This energy can be destructive, particularly at higher operat-
Thermal and short-circuit protection are included in the
The winding current can be monitored with the I
With a 50% duty cycle the average voltage of outputs
Four-quadrant operation allows for smooth transitions
and B
OUT
will be the same, which is half of V
+
DD
. Both pairs of output
S
SA56U REV A FEBRUARY 2007 © 2007 Apex Microtechnology Corp.
and P
GND
S
so that the
pins may
SEN
pin
Short-circuit protection – The short-circuit protection circuits
will sense a direct short from either output (A
P
protection circuit engages, it will place all four MOSFETs in
the tristate state (high-impedance output). The SC output, pin
6, will go HIGH though not latch, thereby denoting that this
protection feature has been triggered.
Over-current protection – When the current on the high side
goes above 10 amperes peak, the over-current circuit tristates
so that the four MOSFETs go into a latched fault condition.
Thermal protection – The thermal protection circuits will en-
gage if the temperature of any of the four MOSFETs reaches
approximately 160°C. If this occurs, the FAULT output pin will
go HIGH. If the thermal protection circuit engages, it will place
all four MOSFETs in the tristate state (high-impedance output).
The T
not latch, thereby denoting which of the protection features
has been triggered.
PROGRAMMABLE CURRENT LIMIT
output current of the active P channel output MOSFET. The
proportionality is approximately 200 microamperes per ampere
of output current. Note that the I
the switching transitions when current spikes are likely to be
significant.
from I
an internally-generated 2.75V threshold, all four output MOS-
FETs will be turned off for the remainder of the switching cycle.
A 2.7k-Ohm resistor will set the current limit at approximately
5 amperes.
control loop in torque motor applications.
CURRENT SENSE LINEARITY CALCULATION
2 and is calculated using the method described below:
a) Define a straight line (y = mx + b) joining the two end data
b) Calculate linear I
c) Determine deviation from linear I
GND
The I
The I
The current sense linearity is specified in the table on page
points where, m is the slope and b is the offset or zero
crossover. Calculate the slope m and offset c using the
extreme data points. Assume I
in the x axis.
the straight line equation derived in step (a) for the I
data points.
measured I
To create a programmable current limit, connect a resistor
or V
SEN
LIM
SEN
SEN
output which is normally LOW will go HIGH, though
to SIG
S
output can also be used for maintaining a current
pin sources a current proportional to the forward
– as well as across the load. If the high-current
SENSE
GND
. If the voltage across this resistor exceeds
value (IS
SEN
(or ideal I
ACTUAL
SEN
SENSE
) as shown below:
SENSE
output is blocked during
SEN
in the y axis and I
value, IS
(step (b) and actual
OUT
SA56
IDEAL
or B
) using
OUT
LOAD
LOAD
) to
7