DC1312A - Demo Manual

DEMO CIRCUIT 1312
QUICK START LT3689
GUIDE
LT3689
Monolithic 700mA Step-Down Regulator with
Power-On Reset and Watchdog Timer
DESCRIPTION
Demonstration circuit 1312 is a Monolithic 700mA
Step-Down Regulator with Power-On Reset and
Watchdog Timer featuring the LT3689. The board
operates from inputs up to 36V and withstands
transients up to 60V. Output is 3.3V, 700mA. When
output current is low, the circuit operates in Burst
Mode. Users can popular R7 on the EN/UVLO pin
to provide a programmable under voltage lockout.
Fault protections are provided through power
switch current limit, switching frequency fold back
and thermal shutdown, etc.
abled by JP2. Circuit can be synchronized to an
external clock connected to SYNC turret. If SYNC
function is used, the Rt resistor should be chosen
to set the LT3689 internal switching frequency at
least 20% below the lowest synchronization input
frequency.
The power-on reset and watchdog timer periods
are independently adjustable using external capacitors. Tight accuracy specifications and glitch
immunity ensure reliable operation of the circuit.
Window mode or time out mode is selectable
through JP1. Watchdog can be enabled or dis-
Design files for this circuit board are available.
Call the LTC factory.
PERFORMANCE SUMMARY
SYMBOL
VIN
VOUT
IOUT
IQ
EFF
TWDU
TWDL
TRST
PARAMETER
Input Supply Range
Output Voltage Range
Output Current
No Load Quiescent Current
Efficiency
Watchdog Upper Boundary Period
Watchdog Lower Boundary Period
Programmed Reset Period
The LT3689 datasheet gives complete descriptions
of the part, operation and application information.
The datasheet must be read in conjunction with
this quick start guide for working on or modifying
the demo circuit 1327.
L, LTC, LTM, LT, Burst Mode are registered trademarks of Linear Technology
Corporation. Other product names may be trademarks of the companies that manufacture the products.
Specifications are at TA = 25°C
CONDITIONS
VOUT=3.3V
No load
VIN = 12V, IOUT = 700mA
C3=10nF
C3=10nF
C4=10nF
MIN
4.5
3.2
0
TYP
3.3
77
82
182
5.88
23
MAX
36
3.4
700
UNITS
V
V
mA
uA
%
ms
ms
ms
1
LT3689
QUICK START PROCEDURE
Demonstration circuit 1312 is easy to set up to
evaluate the performance of the LT3689. Refer to
0 for proper measurement equipment setup and
follow the procedure below:
NOTE. When measuring the input or output voltage ripple, care
must be taken to avoid a long ground lead on the oscilloscope
probe. Measure the input or output voltage ripple by touching the
probe tip directly across the terminals of the input or output
capacitors. See Figure 2 for proper scope probe technique.
1. Place jumpers in the following positions:
JP1 T or W (bar)
JP2 ON or OFF (When OFF, watchdog disabled)
2. With power off, connect the input power supply
to VIN and GND.
3. With power off, connect the load to VOUT and
GND.
2
4. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed 36V.
5. Check for the
VOUT=3.3V
proper
output
voltages.
NOTE. If there is no output, temporarily disconnect the load to
make sure that the load is not set too high or is shorted.
6. Once the proper output voltage is established,
adjust the loads within the operating range and
observe the output voltage regulation, ripple
voltage, efficiency and other parameters.
7. To test watchdog timer, connect a clock input to
the WDI terminal. Observe output at the WDO
terminal while the clock parameters are adjusted.
8. To test Power-On reset, observe output at the
RESET terminals.
LT3689
Figure 1. Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
3
LT3689
4
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