DC1359A - Demo Board Manual

DEMO CIRCUIT 1359
QUICK START LT3640
GUIDE
LT3640
Dual Monolithic Buck Regulator with PowerOn Reset and Watchdog Timer
DESCRIPTION
Demonstration circuit 1359 is a Dual Monolithic Buck
Regulator with Power-On Reset and Watchdog Timer
featuring the LT3640. The board operates from inputs up
to 35V and withstands transients up to 55V. The outputs
are 3.3V, 0.8A and 1.2V, 1A. At light loads, both regulators operate in low ripple Burst Mode® to maintain high
efficiency and low output ripple. Users can populate R13
on the EN/UVLO pin to provide a programmable under
voltage lockout. Both channels have cycle-by-cycle current limit, providing protection against shorted outputs.
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. Watchdog can be enabled or
disabled by JP1.
The circuit can be synchronized to an external clock connected to the SYNC terminal. If the SYNC function is
used, the Rt resistor (R9) should be chosen to set the
LT3640 internal switching frequency at least 20% below
the lowest synchronization input frequency.
The LT3640 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
1359.
Design files for this circuit board are available. Call
the LTC factory.
L, LTC, LTM, LT are trademarks of Linear Technology Corporation. Other product names
may be trademarks of the companies that manufacture the products.
PERFORMANCE SUMMARY Specifications are at TA = 25°C
SYMBOL
PARAMETER
VIN
Input Supply Range
VOUT1
VOUT2
IOUT1
IOUT2
IQ
Output Voltage 1
Output Voltage 2
Output Current 1
Output Current 2
No Load Quiescent Current
FSW
TWDU
TWDL
TRST
Switching Frequency
Watchdog Upper Boundary Period
Watchdog Lower Boundary Period
Programmed Reset Period
CONDITIONS
VOUT1 = 3.3V, IOUT1 = 0.8A
VOUT2 = 1.2V, IOUT2 = 1A
VIN = 12V, IOUT1 = 0.8A
VIN = 12V, IOUT2 = 1A
MIN
5
3.20
1.16
0
0
VIN = 12V, VOUT1 = 3.3V, VOUT2 = 1.2V, No
Load
MAX
35
3.30
1.20
2
55.5
3.5
55.5
UNITS
V
3.40
1.24
0.8
1
V
V
A
A
mA
2.35
MHz
ms
ms
ms
0.33
1.75
C7 = 1500pF
C7 = 1500pF
C8 = 1500pF
TYP
1
LT3640
QUICK START PROCEDURE
Demonstration circuit 1359 is easy to set up to evaluate
the performance of the LT3640. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
5. Check for the proper output voltages:
1. Place Jumper JP1 in the following position:
6. Once the proper output voltages are established, adjust the loads within the operating range and observe
the output voltage regulation, ripple voltage, efficiency
and other parameters.
OFF: Watchdog Disabled
ON: Watchdog Enabled
2. With power off, connect the input power supply to VIN
and GND.
3. With power off, connect loads from VOUT1 to GND
and VOUT2 to GND.
4. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed 35V.
2
VOUT1 = 3.3V, VOUT2 = 1.2V
NOTE. If there is no output, temporarily disconnect the load to make sure
that the load is not set too high or is shorted.
7. To test the watchdog timer, connect a clock input to
the WDI terminal. Observe the output at the WDO terminal while the clock parameters are adjusted.
8. To test Power-On Reset, observe output at the RESET
terminals: RST1 and RST2.
LT3640
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
3
LT3640
4
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