DC611A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 611
DUAL, SPREAD-SPECTRUM, LOW NOISE, INDUCTORLESS STEP DOWN DC/DC CONVERTER
LTC3252
DESCRIPTION
Demonstration circuit 611 is a dual, spread-spectrum, step
down charge pump DC/DC converter featuring the
LTC®3252EDE. It produces regulated 1.5V and 1.2V
output voltages at up to 250mA of output current each from
2.7V to 5.5V input. The unique spread spectrum
architecture of the LTC3252 provides highly efficient and
low noise operation. The circuit has a low external parts
count and requires only five small surface mount capacitors
and four tiny surface mount resistors. DC611 demonstrates
appropriate layout techniques for the LTC3252 inductorless
DC-DC converter. This power supply circuit is ideally
suited for space-constrained battery-powered applications
that require small size and low operating current.
Design files for this circuit board are available.
Call the LTC factory.
LTC is a registered trademark of Linear Technology Corporation.
QUICK START PROCEDURE
Demonstration circuit 611 is easy to set up and evaluate the
performance of the LTC3252. Refer to Figure 1 for proper
measurement equipment setup and follow the procedure
below:
1.
With power off, connect input power source to VIN and
GND terminals. Input voltage range is limited to
between 2.7V and 5.5V for the 1.2V output and
between 3.21V and 5.5V for the 1.5V output.
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 VIN,
VOUT1 or VOUT2 and GND terminals. See Figure 2 for proper
scope probe technique.
2.
Place selector jumper JP1 in the ON position to enable
VOUT1 (1.5V), and jumper JP2 in the ON position to
enable VOUT2.
3.
If desired, loads may be connected from VOUT1 to GND
and from VOUT2 to GND. The following VIN (min) vs.
load chart must be followed to ensure correct
regulation of VOUT1 and VOUT2:
Table 1. VIN VS. LOAD CHART
VIN (min) vs load
VIN (MIN)
IOUT1
IOUT2
3.5V
250mA
250mA
3.2V
100mA
250mA
3.1V
50mA
250mA
2.9V
---
250mA
2.7V
---
150mA
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 611
DUAL, SPREAD-SPECTRUM, LOW NOISE, INDUCTORLESS STEP DOWN DC/DC CONVERTER
NOTE: VOUT1 is in dropout for VIN < 3.0V and will cause the
LTC3252 to operate in continuous mode instead of the
more efficient burst mode. To monitor the actual
performance of VOUT2 for VIN <3.1V, VOUT1 should be
disabled by placing jumper JP1 in the OFF position.
4.
Turn on the power at the input.
NOTE: Make sure that the input voltage does not exceed
VOUT2 = 1.2V. If there is no output, temporarily disconnect
the load to make sure that the load is not set too high.
6. Once the proper output voltages are established, adjust
the loads up to 250mA and observe the output voltage
regulation, input and output ripple voltage, efficiency and
other parameters. Remember to follow the VIN (min) vs.
load chart for correct regulation of VOUT1 and VOUT2.
5.5V.
5. Check for the proper output voltages. VOUT1 = 1.5V and
Figure 1. Proper Measurement Equipment Setup
Figure 2. Scope Probe Placement for Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 611
DUAL, SPREAD-SPECTRUM, LOW NOISE, INDUCTORLESS STEP DOWN DC/DC CONVERTER
3
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