The clock frequency is internally set to a frequency of ap-
proximately 400kHz. The CLK OUT pin will normally be tied
to the CLK IN pin. The clock is divided by two and applied to
an RC network which produces a ramp signal at the –PWM/
RAMP pin. An external clock signal can be applied to the CLK
IN pin for synchronization purposes. If a clock frequency lower
than 400kHz is chosen an external capacitor must be tied to
the –PWM/RAMP pin.This capacitor, which parallels an internal
capacitor, must be selected so that the ramp oscillates 4 volts
p-p with the lower peak 3 volts above ground.
PWM INPUTS
The full bridge driver may be accessed via the pwm input
comparator. When +PWM > -PWM then A OUT > B OUT. A
motion control processor which generates the pwm signal can
drive these pins with signals referenced to GND.
PROTECTION CIRCUITS
A fixed internal current limit senses the high side current.
Should either of the outputs be shorted to ground the high side
current limit will latch off the output transistors. The temperature
of the output transistors is also monitored. Should a fault condi-
tion raise the temperature of the output transistors to 165°C
the thermal protection circuit will latch off the output transistors.
The latched condition can be cleared by either recycling the
V
CC
and +V
S
power or by toggling the I LIMIT/SHDN input with
a 10V pulse. See Figures A and B. The outputs will remain off
as long as the shutdown pulse is high (10V).
When supply voltage is over 100V, these circuits may not
protect the FET switches in the case of short circuits directly
at the pins of the amplifier. However, a small inductance be-
tween the amplifier and the short circuit will limit current rise
time and the protection circuits will be effective. A pair of 12
inch wires is adequate inductance.
BYPASSING
CURRENT LIMIT
I SENSE A
Adequate bypassing of the power supplies is required for
proper operation. Failure to do so can cause erratic and low
efficiency operation as well as excessive ringing at the out-
puts. The Vs supply should be bypassed with at least a 1µF
ceramic capacitor in parallel with another low ESR capacitor
of at least 10µF per amp of output current. Capacitor types
rated for switching applications are the only types that should
be considered. The bypass capacitors must be physically
connected directly to the power supply pins. Even one inch of
lead length will cause excessive ringing at the outputs. This
is due to the very fast switching times and the inductance of
the lead connection. The bypassing requirements of the Vcc
supply are less stringent, but still necessary. A .1µF to .47µF
ceramic capacitor connected directly to the Vcc pin will suffice.
There are two load current
R LIMIT
sensing pins, I SENSE A and
I SENSE B
I SENSE B. The two pins can
5K
be shorted in the voltage
I LIMIT/SHDN R
SHUTDOWN
FILTER
SIGNAL
mode connection but both
0/10V
must be used in the current
IN4148
C FILTER
mode connection (see figures
A and B). It is recommended
FIGURE A. CURRENT LIMIT WITH
that R
LIMIT
resistors be non-
SHUTDOWN VOLTAGE MODE.
inductive. Load current flows
in the I SENSE pins. To avoid errors due to lead lengths connect
the I LIMIT/SHDN pin directly to the R
LIMIT
resistors (through
the filter network and shutdown divider resistor) and connect
MODULATION RANGE
The high side of the all N channel H-bridge is driven by a
bootstrap circuit. For the output circuit to switch high, the low
side circuit must have previously been switched on in order to
charge the bootstrap capacitor. Therefore, if the input signal
to the SA12 demands a 100% duty cycle upon start-up the
output will not follow and will be in a tri-state (open) condition.
The ramp signal must cross the input signal at some point to
correctly determine the output state. After the ramp crosses the
input signal one time the output state will be correct thereafter.
In addition, if during normal operation the input signal drives
the SA12 beyond its linear modulation range (approximately
95%) the output will jump to 100% modulation.
SA12U
4
SA12
POWER SUPPLY SEQUENCING
The V
CC
power supply voltage must be applied prior to the +V
S
power supply voltage. The output stage devices will be damaged
if the V
CC
supply is not present when the +V
S
supply is applied. Always sequence the V
CC
supply prior to the +V
S
supply.
CONTACTING CIRRUS LOGIC SUPPORT
For all Apex Precision Power product questions and inquiries, call toll free 800-546-2739 in North America.
For inquiries via email, please contact apex.support@cirrus.com.
International customers can also request support by contacting their local Cirrus Logic Sales Representative.
To find the one nearest to you, go to www.cirrus.com
IMPORTANT NOTICE
Cirrus Logic, Inc. and its subsidiaries ("Cirrus") believe that the information contained in this document is accurate and reliable. However, the information is subject
to change without notice and is provided "AS IS" without warranty of any kind (express or implied). Customers are advised to obtain the latest version of relevant
information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale
supplied at the time of order acknowledgment, including those pertaining to warranty, indemnification, and limitation of liability. No responsibility is assumed by Cirrus
for the use of this information, including use of this information as the basis for manufacture or sale of any items, or for infringement of patents or other rights of third
parties. This document is the property of Cirrus and by furnishing this information, Cirrus grants no license, express or implied under any patents, mask work rights,
copyrights, trademarks, trade secrets or other intellectual property rights. Cirrus owns the copyrights associated with the information contained herein and gives con-
sent for copies to be made of the information only for use within your organization with respect to Cirrus integrated circuits or other products of Cirrus. This consent
does not extend to other copying such as copying for general distribution, advertising or promotional purposes, or for creating any work for resale.
CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF DEATH, PERSONAL INJURY, OR SEVERE PROP-
ERTY OR ENVIRONMENTAL DAMAGE (“CRITICAL APPLICATIONS”). CIRRUS PRODUCTS ARE NOT DESIGNED, AUTHORIZED OR WARRANTED TO BE
SUITABLE FOR USE IN PRODUCTS SURGICALLY IMPLANTED INTO THE BODY, AUTOMOTIVE SAFETY OR SECURITY DEVICES, LIFE SUPPORT PROD-
UCTS OR OTHER CRITICAL APPLICATIONS. INCLUSION OF CIRRUS PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUS-
TOMER’S RISK AND CIRRUS DISCLAIMS AND MAKES NO WARRANTY, EXPRESS, STATUTORY OR IMPLIED, INCLUDING THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR PARTICULAR PURPOSE, WITH REGARD TO ANY CIRRUS PRODUCT THAT IS USED IN SUCH A MANNER. IF THE
CUSTOMER OR CUSTOMER’S CUSTOMER USES OR PERMITS THE USE OF CIRRUS PRODUCTS IN CRITICAL APPLICATIONS, CUSTOMER AGREES,
BY SUCH USE, TO FULLY INDEMNIFY CIRRUS, ITS OFFICERS, DIRECTORS, EMPLOYEES, DISTRIBUTORS AND OTHER AGENTS FROM ANY AND ALL
LIABILITY, INCLUDING ATTORNEYS’ FEES AND COSTS, THAT MAY RESULT FROM OR ARISE IN CONNECTION WITH THESE USES.
Cirrus Logic, Cirrus, and the Cirrus Logic logo designs, Apex Precision Power, Apex and the Apex Precision Power logo designs are trademarks of Cirrus Logic, Inc.
All other brand and product names in this document may be trademarks or service marks of their respective owners.
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