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The EK22 evaluation kit is designed to provide a convenient
way to breadboard design ideas for the SA56 PWM amplifiers.
The EVAL25 evaluation board is pre-wired for all required
and recommended external components. The EVAL25 also
includes a breadboard area for constructing your application
circuit including provisions for an output filter. Please refer to
applications note 32 in the Apex catalog for guidance in filter
component selection. The 1µF ceramic capacitors supplied
with the kit are for high frequency bypassing of the VS and
VDD supplies (C1 – C3 on the EVAL25 board). An additional
user supplied low ESR capacitor of at least 10uF per amp
of output current is required for adequate bypass of the VS
supply (C4 on the EVAL25 board). Please refer to applications note 30 for help with power supply bypassing and other
useful information.
This evaluation kit is supplied for evaluation of SA56 prototype beta samples. There are some limitations to the SA56
prototypes that must be noted. Suggestions to minimize the
effect of these limitations are included.
The SA56 combines both high speed high power switching
and low level analog signals on a single silicon chip. The difficulty in achieving clean noise free operation is much greater
then that of discrete or hybrid microcircuit designs. Though
much care and attention has been given to these considerations
in the design and layout of the SA56, there is still some work
to be done and these prototypes do not switch as cleanly as
necessary for completely trouble free operation.
Grounding for the SA56 is critical. The EVAL25 board has
separate ground paths for signal ground (SGND) and power
ground (PGND). The signal and power grounds are common
at one point on the SA56. Ground loops can be formed if these
two grounds are tied together externally. These two grounds
are not tied together on the EVAL25 board through trace routing. When building your evaluation circuit, insure that each
component referenced to ground is tied to the proper ground
path. External components at the high speed, high current
output of the SA56 must be returned to PGND.
Analog Mode Operation of the SA56 prototype is affected
by switching noise through non-linear operation towards the
PWM duty cycle extremes. This limits the useable duty cycle
range of the SA56 prototype. The use of external flyback
diodes and the use of RC snubbers from each output to
ground reduces switching noise, increasing the usable duty
cycle range. However the duty cycle should be limited within
the range of 5% to 95%.
This kit is supplied with four schottky diodes, p/n SB5100,
for use as external flyback diodes (D1 – D4). It is recommended that diodes D1 – D4 be used regardless of the mode
of operation.
In addition four 20 ohm, 5W resistors, and two 15nF, 100V
capacitors are supplied for use as an RC snubber for each
output (C9, R3a, R3b and C10, R4a, R4b). The snubbers are
especially useful in reducing the noise generated by the high
dv/dt during output switching. The power dissipated in the
snubber components can be estimated by;
P = V2 * C * FSW
P is the power dissipated
V is the VS supply voltage
C is the snubber capacitor value (15nF)
FSW is the switching frequency.
It also is recommended that a low pass RC filter be included
on the PWM_IN line for analog mode operation (R2 and C8).
A 100 ohm resistor and 2.7nF capacitor worked well for R2
and C8 value during design verification testing. However these
may not be the best choice for switching frequency and load
configurations other then that used during design verification
testing. It is up to the user to determine the best values to use
for a given application.
Start-up Faults of the SA56 protection circuits due to noise
generated by high current transient pulses at start-up may
occur. The SA56 has an internal start-up reset pulse to handle
these transients, but the duration of these transients is often
longer then the reset pulse.
These transient current pulses will trip the short circuit and
over current protection if a high current output is commanded
at start-up. It is best if the SA56 can be started up with low
output current demand. Examples are starting with the PWM
input at mid-range in analog mode, or starting with reduced
VS supply voltage.
If a “soft start” is not practical, a start-up reset pulse can be
generated on the EVAL25 board with a few external components. Figure 1 is an example of this reset pulse generator.
When VDD is applied, the disable pin will be pulled high by
capacitor C11 until C11 is discharged by R1. This generates
a reset pulse on the disable pin. After the reset pulse is discharged, R1 holds disable at logic low for normal operation. The
time constant of C11 and R1 must be a couple of milliseconds
longer then the rise time of the VDD supply. A good choice
for R1 is 10K - 20K ohms. The VS supply must be turned on
before the VDD supply.
4(/% 4(/%
Figure 1. Start-up Reset
APEX MICROTECHNOLOGY CORPORATION • TELEPHONE (520) 690-8600 • FAX (520) 888-3329 • ORDERS (520) 690-8601 • EMAIL [email protected]
It also maybe necessary to bypass the SCin line with a
22pF - 50pF ceramic capacitor. This bypass capacitor will
add a time delay to the short circuit protection. However this
additional time delay has not resulted in failure during design
verification testing of the short circuit protection. The short
circuit protection may be disabled entirely by grounding the
SCin pin to SGND. Cycle by cycle current limiting will still be
active if a current limit resistor is connected from ISEN to
SGND. Please refer to the SA56 data sheet for selection of
the current limit resistor.
The SA56 prototypes have an extended blocking period
in the ISEN output. This blocking period can be several hundreds of nano-seconds. This is a limitation of this feature for
the SA56 prototypes that will be corrected in the production
SA56 when released.
In 2 quadrant mode of operation, one half bridge of the
SA56 is held low while the other half bridge is modulated.
This means that no current is sensed at the ISEN pin during
the low portion of the output modulation. The ISEN output is
not useful for configuring a transconductance amplifier in 2
quadrant operation.
• All Apex amplifiers should be handled using proper ESD
• Do not change connections while the circuit is powered.
• Initially set all power supplies to the minimum operating
voltage allowed in the device data sheet.
• The power supply turn on sequence for the SA56 is VS
supply on first followed by the VDD supply. If VDD is turned
on before VS, the SA56 will start up in a fault condition that
can not be reset until VS is greater then 12V.
--Ref. Apex P/N
Heat Sink
Strip of 30 Cage Jacks 1
PC board
BJ1-12 BJ1
Banana Jack/ 12
Deltron 571-0100
BN1, 2 146510CJ
BNC, PCB mount R/A
Jameco 146510CJ
C1-3 OX7R105KWN
1 µF cap
Novacap 1825B105K201N
C9, 10 C062K153K1X5CA 15 nF cap
D1-4 SB5100
Diode, 100V, 5A
R3a-4b 286-20
Resistor, 20 ohm, 5W
Header 2x7 pin
Jumper, shorting
Thermal Washer
1 box
figure 2 shematic
APEX MICROTECHNOLOGY CORPORATION • TELEPHONE (520) 690-8600 • FAX (520) 888-3329 • ORDERS (520) 690-8601 • EMAIL [email protected]
During assembly, refer to Figure 2, 3 and the SA56 data
1. Note that each side of the circuit board is identified as either
the “component side” or “bottom side”. The component
side is labeled on the silk screen side of the board.
2. Cut the MS11 into strips of 12 and 11. Discard the remaining small strip. Insert the two strips into the two rows of
holes for the DUT from the component side of the PCB.
From the bottom side, solder all cage jacks to the circuit
board pads. Be sure that the cage jacks are fully seated
before soldering. Be careful that the solder does not flow
into the cage jack. Remove the plastic carrier strips.
3. Solder the surface mount capacitors at C1 – C3, on the
component side of the PCB. The carrier strips removed
from the cage jacks in step 2 are convenient as a tool to
hold the capacitors in place while soldering. The carrier
strips can be discarded when no longer needed for this
purpose. Though not required, it is a good idea to fill in
the vias on the PGND side of C2 and C3 with solder.
4. From the component side, insert the 4 diodes D1 – D4 into
the PCB at the locations marked on the board. Solder the
diodes to the PCB from the bottom side.
5. Insert the 14 pin header TB1 into the PCB from the
component side. Solder TB1 from the bottom side. Install
shorting jumpers J1 – J3 on TB1 to configure the mode of
operation for the SA56. Refer to the schematic in figure 2
for jumper positions. The top pair of pins in the schematic
diagram for TB1 correspond to the left most pair of pins
when TB1 is viewed on the PCB in figure 3.
6. Mount the banana jacks and the BNC connectors to the
PCB at locations marked on the PCB as needed or as
desired. Solder these from the bottom side of the board.
7. Mount an electrolytic bypass capacitor (not supplied) at C4
from the component side of the PCB. Match the polarity
markings on the PCB. Solder the capacitor to the PCB
from the bottom side.
8. The SA56 will not function with the ISEN pin open. Select
a resistor value and install on the component side of the
PCB between ISEN and SGND at the R5 position marked
on the PCB. Solder from the bottom side. If a current limit
resistor is not used, short the ISEN pads to SGND in place
of R5.
9. It is recommended that a 10K to 20K pull down resistor be
installed between the disable line and SGND at the location labeled R1. For reliable start-up it is recommended to
include a capacitor and diode to VDD as shown in figure
10. For analog mode operation, a PWM timing capacitor is
required. Refer to the SA56 datasheet for timing capacitor calculation. Install the timing capacitor in the C7 location.
11. Install the snubber components C9, R3a, R3b and C10,
R4a, R4b at the locations labeled on the PCB.
12. If the prototype SA56 will be used in an analog application
it is recommended to include an input RC filter in series
with the PWM_IN input (R2 and C8). The PWM_IN BNC
connector is not routed to the DUT unless a resistor or a
shorting wire is installed at the R2 location.
13. Mount other components to complete your application
circuit, using the pads and holes provided. Trim all excess
14. The PCB has provisions for a 2 pole output filter. The locations for the inductors L1 and L2 are designed to accept
a wide range of sizes for either a through hole or surface
mount style of inductor. J.W. Miller series 6700 through
hole inductors or series PM2110 surface mount inductors
will fit in these locations and include a wide range of inductors suitable for many SA56 applications. These inductors
are readily available from Digikey Corp.
15. Partially insert the SA56 device into the cage jacks from
the Component side of the PCB.
16. Install the HS20 on the component side of the board,
securing the HS20 to the board with two 6-32 self tapping screws (Not supplied) through the elongated holes
in the PCB from the bottom side. Place a TW12 thermal
washer between the DVT and heatsink. Align the holes
in the TW12 to the mounting holes of the DUT.
17. Mount the device to the heat sink with a 4-40 x 1/4“ screw.
Make the screw snug but do not over tighten as this provides no benefit and may break the screw.
18. Hook up power and signals as necessary. The amplifier
is now ready for testing.
• FAX (520)
ORDERS (520)
• [email protected]
This data
sheet has been carefully
checked and is believed
to be reliable,
no responsibility
is assumed
for possible•inaccuracies
or omissions.
All specifications
subject to change without notice.
EK22U REV B MARCH 2006 © 2006 Apex Microtechnology Corp.