SA305 Datasheet, PDF (6/6 Pages) Cirrus Logic – PULSE WIDTH MODULATION AMPLIFIER

SA305
OPERATING
CONSIDERATIONS
GENERAL
Please read Apex Application Note 1 “General Operat-
ing Considerations” which covers stability, power supplies,
heat sinking, mounting, current limit, SOA interpretation, and
cal parasitic oscillation in the output stage of the SA305. Use
electrolytic capacitors at least 10μF per output amp required.
Bypass the electrolytic capacitors with high quality ceramic
specification interpretation. Visit www.apexmicrotech.com for
design tools that help automate tasks such as calculations
capacitors (X7R) 0.1μF or greater. See the external connec-
tions diagram on page 1.
for stability, internal power dissipation, current limit, heat sink
selection, Apex’s complete Application Notes library, Technical
Seminar Workbook and Evaluation Kits.
GROUND PINS
CURRENT SENSE
The current of each phase can be read using the IMON output
pins. The high side of each half bridge current is monitored
separately. The current sense output level is as follows:
Analog and Power Grounds should be connected externally
at only one point on the motor control board in such a way
that there is no current flow through the connection to avoid
noise related issues.
CHANNEL A: 1/4000th of the phase current.
CHANNEL B: 1/3600th of the phase current.
CHANNEL C: 1/3700th of the phase current.
PROTECTION
External power current sense resistors are not required with
Each of the six output devices includes short circuit protec-
tion to prevent damage from direct shorts to GND or VS. The
SA305 is protected against overheating with built in thermal
monitoring. The thermal protection will engage when the tem-
perature of the MOSFETs reach approximately 160°C. The
FAULT output pin will latch “HIGH” if either protection circuits
Y ^{engages and will place all MOSFETs in the “OFF” state (high}
impedance output). The most severe condition for any power
device is a direct, hard-wired (“screwdriver”) short from an
output to ground. While the short circuit protection will latch
R _{the output MOSFETs the die and package may be required}
to dissipate up to 500 Watts of power until the protection is
engaged. This energy can be destructive, particularly at higher
A operating voltages, so good thermal design is critical if such
fault tolerance is required of the system. The Vs and PGND
pins may become very hot during this period of high current.
The SA305 has an internal FAULT latch mechanism by
I ^{N which the device stays disabled (in case a fault occurs) un-}
less the user resets it. If the SA305 goes into FAULT condition
because of short-circuit, over current or high temperature,
the DISABLE pin needs to be pulled HIGH (briefly) to reset
the SA305 and resume normal operation. However, before
resetting the SA305 the user has to ensure that the FAULT
I M has been eliminated.
Undervoltage lockout is not required since the power stage
is complimentary and does not need a charge pump to activate
the high side FETs. A True signal on the FAULT pin indicates
that at least one of these protection events has occurred. Once
L a FAULT has occurred, fault condition must be removed in
order for the FAULT signal to be removed.
CONTROL
E _{Each output device is controlled by a single input. There is}
a provision inside the SA305 to prevent the upper and lower
FET of the same channel from being active at the same time
R even though the input controls request that both the N and P
devices from half bridges be on.
P ^{POWER SUPPLY BYPASSING}
the SA305. However, in order to read the current level using a
standard A/D input a resistor of 1KΩ should be shunted across
each output. A standard 1/4W resistor is sufficient here. Motor
current adjustments are made through the PWM inputs. Above
the internal limit the device self-protects.
SA305 OPERATION
The SA305 is used to drive three phase motors but can
be used where ever three high current outputs are required.
A DSP or microcontroller is used to control and monitor the
operation of the SA305.
The current through each of the three P channel drive
transistors is monitored by on-board circuitry. Current is set
using the PWM inputs which drive each FET independently.
Once the desired level is reached the inductance of the mo-
tor keeps the current near the programmed level. Should the
current get to the internally set 12A level, the driver is shutoff
to protect itself.
Whenever there are no “fault” conditions and the input controls
indicate an output should be on, the P and N drivers will turn
on. If the input controls are requiring that P-channel turn on
before the N-channel turns off, the SA305 will automatically
delay the P-channel turn on. The time between the N turning
off and the P turning on or the P channel turning off and the
N channel turning on is called dead time. An internally set
minimum dead time assures no “shoot through” current and
gives the clamp diode time to discharge.
The warning temperature setting is fixed at Tj= 135C. When
the junction temperature gets to the programmed point, the
temperature warning bit will be set. It will be reset when the
temperature falls below the programmed limit.
The Fault temperature setting is fixed at Tj= 160C. Once
the Fault temperature has been reached the Fault Output
goes high and the outputs of the device are disabled. This
output can be used as a microcontroller interrupt. The Fault
latch will not be reset until the temperature is below the fault
temperature setting.
If more than one output is required to be conducting large
Bypass capacitors to power supply terminals +Vs and –Vs
currents at the same time, the maximum current will need to
must be connected physically close to the pins to prevent lo-
be de-rated.
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SA305U REV 3 FEBRUARY 2006 © 2006 Apex Microtechnology Corp.