QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 726
LTC6903 & LTC6904
DESCRIPTION
Demonstration circuit 726 is for the evaluation of
Linear Technology’s programmable oscillator ICs,
the LTC6903 and LTC6904. The DC726A-A features
the LTC6903 IC in an 8-lead MSOP package. The
LTC6903 is a 1kHz to 68MHz oscillator program-
mable thru a 3-wire digital interface compatible with
the SPI serial protocol. The DC726A-B features the
LTC6904 IC in an 8-lead MSOP package. The
LTC6904 is a 1kHz to 68MHz oscillator program-
mable thru a 3-wire digital interface compatible with
the I
2
C serial protocol (a Philips Corp. trademark).
The LTC6903 and LTC6904 require no external
components and operate over a single power sup-
ply range from 2.7V to 5.5V. The maximum fre-
quency error is 1.1% or 1.6% when operating with
a single 3V or 5V power supply respectively.
Demonstration circuit 726 is operated in one of two
modes:
1. A Local Mode using DC726 as stand-alone dem-
onstration board with external power supplies.
2. A QuickEval mode for interfacing to a USB port of
a PC using Linear Technology’s DC590 Serial Con-
troller Board and a QuickEval program for Windows
98
or
later
downloaded
from
www.linear.com/software.
In Local Mode, a 16-bit serial code is entered in
HEX with push-button switches to a 4-digit LED
display. The HEX code is read by PIC (Peripheral
Interface Controller) that updates the control word
of the LTC6903/LTC6904.
In QuickEval Mode, the DC726 PIC shuts down
when it is connected to a DC590A. Control of the
LTC6903/LTC6904 is thru a PC with a QuickEval
program which uses either a frequency or a HEX
code input. The frequency or HEX code input en-
tered on the computer display, is sent as a 16-bit
serial word to the DC726A-A/B.
Design files for this circuit board are available.
Call the LTC Factory.
LTC is a trademark of Linear Technology Corporation
PROGRAMABLE CLOCK 1KHZ TO 68MHZ
Demonstration Circuit 726A-A
(Provides an LTC6903CMS8 with SPI serial interface)
Demonstration Circuit 726A-B
(Provides an LTC6904CMS8 with I C serial interface)
Features
Fout Range: 1.039kHz to 68MHz
High Speed Inverters for driving coax cables
Flexible 3V to 5V operation of a LTC6903/04
Local Mode
for stand-alone operation (No PC re-
quired)
QuickEval Mode
for PC input with a Quick Eval pro-
gram
2
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 726
PROGRAMABLE CLOCK 1KHZ TO 68MHZ
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 726
PROGRAMABLE CLOCK 1KHZ TO 68MHZ
A “LOCAL MODE” TEST PROCEDURE
1.
Using Figure 1 as a guide, connect to a DC726 a
5V and 3V power supply and oscilloscope (J2 to
channel 1 and J3 to channel 2).
Set JP2 to the “LOCAL” position.
Set SW1 to ON and SW2 to OFF.
Turn Power On.
A. If a DC726A or B is powered-up for the first
time then the four digit LED display on the
board should read 0 0 0 0 and channel 1 of
the oscilloscope should show a 1.039kHz
square-wave (LEDs 1 is On and LED 2 is
Off).
2.
3.
4.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 726
A “LOCAL MODE” TEST PROCEDURE
1. Using
Figure 1
as a guide, connect to a DC726 a
5V and 3V power supply and oscilloscope (J2 to
channel 1 and J3 to channel 2).
2. Set JP2 to the “LOCAL” position.
3. Set SW1 to ON and SW2 to OFF (the ON position
is to the left).
4. Turn Power On.
A. When a DC726 is powered-up for the first time
the four digit LED display on the board will read 0 0
0 0 and channel 1 of the oscilloscope will show a
1.039kHz square-wave (LED 1 is On and LED 2 is
Off).
B. If a DC726 is powered-up after it has been used
to set the on-board clock to a frequency other than
1.039kHz, the four digit LED display will indicate the
hex code that represents the frequency setting
stored previously using SW8.
C. Set the LED display to the hex code for a
3.2MHz clock frequency (bAbA, see
Example
next
page).
D. Oscilloscope channel 1 should show a 3.2MHz
square-wave with a “low” voltage at 0V and a
“high” voltage equal to Vclk (Vclk is the voltage of
the external power supply connected to VCLKIN.
The clock period is 312.5 nS).
E. Set SW2 to ON.
F. Oscilloscope channel 2 should show the inverted
version of the square-wave shown on channel 1 and
the least significant hex digit on the LED display
should change to 8 (the PIC controller reads the
SW2 position and updates the LED display).
PROGRAMABLE CLOCK 1KHZ TO 68MHZ
A “QUICKEVAL” TEST PROCEDURE
(The QUICKEVAL DEMO PROGRAM must be
loaded and running on a PC.
Downloading the Quick Eval System Software
Go to
www.linear.com
Click on “Design
Support”
Click on “Design
Simulation and Device Models”
Click on “Download” under
“Quick
Eval System Software”
NOTE!
the “
QuickEval-II System Software
”
is not required for DC726 evaluation.
1. Using
Figure 2
as a guide, connect to a DC726 a
Linear Technology DC590 QuickEval serial control-
ler card with a 14-conductor ribbon cable (to J1), a
voltmeter (the plus lead to VQE and minus lead to
GND) and an oscilloscope (J2 to channel 1 and J3
to channel 2).
2. Using a USB cable connect the DC590 controller
to a USB port of a PC.
3. Set JP2 to the “QUICK EVAL” position.
4. Set SW1 to ON and SW2 to OFF.
5. Run the QuickEval program
A. The PC display will show a QuickEval program
window with the following prompt:
Found Device LTC6903 (or LTC6904)
Click OPEN to begin the QuickEval program window
and the user input window will appear (see Figures
3 or 4).
B. The voltmeter should read 5V ±0.25V (this is the
voltage supplied by the QuickEval board).
C. Enter a clock frequency or a Hex code in the user
input window and observe the corresponding
change of the DC726 output on the oscilloscope
display.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 726
PROGRAMABLE CLOCK 1KHZ TO 68MHZ
SETTING THE 4-DIGIT LED DISPLAY
The frequency of an LTC6903/LTC6904 output (f
clk
)
is a function of a divider variable OCT and a fre-
quency range variable DAC. A 4-bit binary number
OCT, a 10-bit binary number DAC and a 2-bit binary
number for output control make up the 16-bit serial
control word (Tables 1 to 3).
On DC726 board the 4-digit LED display must be
set to a HEX code that is the equivalent to a 16-bit
control word for a specified frequency. Using any of
the UP, DOWN, LEFT or RIGHT switches (SW4-
SW7) on a DC726 board will instantly update the
clock frequency, f
clk.
SW8 stores a hex setting and
switches SW1 and SW2 turn on or off the clock
output at J2 and J3 respectively (the ON position
for SW1 and SW2 is to the left).
A DC726 can be set to a specific clock frequency by
connecting a frequency counter to a J2 or J3 output
and toggling SW5-SW7 until the desired frequency
is shown on the counter display. In addition, the 4-
digit LED display can be set to a Hex code corre-
sponding to a specified f
clk
by using the following
conversion:
f
clk
to 4-digit HEX Conversion
1. Specify a clock frequency, f
clk
and use Table 1 to
find the OCT number.
2. Convert the OCT decimal number to hex. The
OCT number in hex is the Hex digit #1 (see Table 2
and Figure 5).
3.2MHz is in the frequency range corresponding to
OCT number 11(Table 1). Decimal 11 is in hex
number
b
(Table 4).
3. Use the DAC equation to calculate the DAC deci-
mal number.
In the above
Example,
the DAC decimal number
for OCT 11 and f
clk
3.2MHz is equal to 686 (to the
nearest integer).
4. Convert the DAC decimal number to a binary
number. The binary equivalent of decimal 686 is
1010101110.
5. Convert the D11 to D8 digits of the DAC binary
number to a hex equivalent number (Hex digit #2).
For the
Example
, the first four most significant bi-
nary digits are 1010 and the hex equivalent is
A.
6. Convert the D7 to D4 digits of the DAC binary
number to a hex equivalent number (Hex digit #3).
For the
Example
, the first four most significant bi-
nary digits are 1011 and the hex equivalent is
b.
7. Hex digit #4 must be set to a hex number that is
the binary equivalent of the two least significant
binary digits of the DAC binary number (D3 and D2)
grouped with the two output control digits D1 and
D0 (see table 2 and 3).
For the
Example
, the last two digits of the DAC bi-
nary number are 10 and the output control digits
are 10 (see table 3) and the four least significant
digits of the 16-bit control word should be 1010
and the hex equivalent for digit #4 is
A.
The 4-digit hex code for the
Example
is
bAbA.
Example
:
Set
f
clk
to
3.2MHz
with J2 output ON and J3 output OFF.
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