DC1541A - Demo Manual

36V, 2.6A Monolithic
Buck Regulator with Dual LDO
Demonstration circuit 1541A is an adjustable 2.6A
Monolithic Buck Regulator with Dual LDO featuring
LT3694/LT3694-1. The buck regulator is capable of generating up to 1.7A at its output while the two LDO regulators are capable of 450mA each. Each regulator has independent track/soft-start circuits simplifying power
supply sequencing and interfacing with microcontrollers
and DSPs.
regulated wall transformers, lead acid batteries and distributed power supplies. The LT3694 can be synchronized to an external clock with the SYNC pin. The
LT3694-1 offers a CLKOUT pin allowing other DC/DC
converters to synchronize to the LT3694-1 clock.
The switching frequency of the board is set to 800kHz.
The high switching frequency permits the use of small
inductors and ceramic capacitors leading to very small
triple output solutions. The constant switching frequency,
combined with low impedance ceramic capacitors, results in low, predictable output ripple. The board is robust against outputs shorting to ground fault.
The LT3694/LT3694-1 datasheet gives a complete description of the part, operation and application information. The datasheet must be read in conjunction with this
quick start guide for demo circuit 1541A.
With its wide input voltage range of 4V to 36V, the
LT3694/LT3694-1 regulates a broad array of power
sources from 4-cell batteries and 5V logic rails to un-
The LT3694/LT3694-1 regulator is available in the thermally enhanced low profile 28-lead (4mm × 5mm) UFD
and FE packages.
Design files for this circuit board are available. Call
the LTC factory.
L, LTC and LT are registered trademarks of Linear Technology Corporation. VLDO is a trade
mark of Linear Technology Corporation. Other product names may be trademarks of the
companies that manufacture the products.
Performance Summary ( TA = 25oC )
Input Voltage Range
Output Voltage VOUT1
Output Voltage VOUT2
Output Voltage VOUT3
Output Current IOUT1
Output Current IOUT2
Output Current IOUT3
Switching Frequency
VOUT1 Buck Efficiency
VOUT1 = 3.3V, IOUT1 = 1.7A
VOUT2 = 2.5V, IOUT2 = 450mA
VOUT3 = 1.8V, IOUT3 = 450mA
VIN = 12V, IOUT1 = 1.7A
VIN = 12V, IOUT2 = 450mA
VIN = 12V, IOUT3 = 450mA
VIN = 12V, IOUT1 = 1.7A,
IOUT2 = 0A, IOUT3 = 0A
4.5V to 36V
3.3V ± 3%
2.5V ± 3%
1.8V ± 3%
0 to 1.7A
0 to 450mA
0 to 450mA
800kHz ± 10%
85% ± 2%
Demonstration circuit 1541A is easy to set up to evaluate
the performance of the LT3694/LT3694-1. Refer to Figure 1 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. With power off, connect the input power supply to
VIN and GND. Connect loads between output terminals (VOUT1, 2 or 3) and GND.
NOTE. Active loads may overload the outputs due to the initial in-rush
current. Change to resistive loads if necessary.
2. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed 36V.
NOTE. The input capacitor C2 is a 50V ceramic capacitor. When testing
70V transient protection function on the input, this capacitor may need
to be replaced with 100V ceramic capacitors.
3. Check for the proper output voltages.
VOUT1=3.3V, VOUT2=2.5V, VOUT3=1.8V
NOTE. If there is no output, temporarily disconnect the load to make
sure that the load is not set too high or is shorted.
4. Once the proper output voltage is established, adjust
the loads within the operating range and observe the
output voltage regulation, efficiency and other parameters.
NOTE. Make sure that the power dissipation is limited.
Figure 1. Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple