DC912A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 912
BOOST AND INVERTING DC/DC CONVERTERS
LT3487EDD
DESCRIPTION
Demonstration circuit 912 features the LT®3487EDD.
The demo circuit demonstrates small size and low
component count in a Boost Circuit and an Inverting
Circuit. The Boost Converter is designed to convert a
3V-5V input to 15V output at 45mA-90mA maximum
load. The Inverting Circuit generates a -8V output at
90mA-150mA maximum load from the same input.
Since the maximum Vin of the LT3487EDD is 16V,
this Demo circuit will work well at higher inputs. The
only limitation is that the input has to be lower than
the Boost converter output (15V) in order to stay in
regulation. If Vin and VBAT will be powered separately, cut trace as indicated on farside of board and
use “VBAT” pad on top.
The LT3487EDD features integrated Schottky diodes
for both outputs and requires only one resistor (per
output) to set the output voltage. Internal sequencing
disables switching on the negative supply until the
positive has reached 87% of its final value. Both circuits are designed to demonstrate the capacitor programmable Soft-Start feature with a single capacitor,
advantages of the 2MHz constant switching frequency and the internal 32V switches. Both outputs
on this demo circuit can be modified for higher voltages. These circuits are intended for space-conscious
applications such as CCD Bias, TFT LCD Bias, OLED
Bias and +/- Rail Generation for Op Amps.
Design files for this circuit board are available. Call
the LTC factory.
LT is a trademark of Linear Technology Corporation
Table 1. Performance Summary (TA = 25°C)
PARAMETERS FOR 15V BOOST CIRCUIT
CONDITION
VALUE
Minimum Input Voltage
3V
Maximum Input Voltage
5V
Output Voltage VOUT
VIN = 3V, IOUT = 0mA to 45mA
15V ±5%
Output Voltage VOUT
VIN = 5V, IOUT = 0mA to 90mA
15V ±5%
Maximum Output Current
Vin = 3V
45mA
Maximum Output Current
Vin = 5V
90mA
Typical Output Ripple VOUT
VIN = 3.3V, IOUT = 45mA
20mVP–P
Typical Efficiency
VIN = 3.6V, Vout = [email protected]
77%
PARAMETERS FOR -8V INVERTING CIRCUIT
VALUE
Output Voltage VOUT
VIN = 3V, IOUT = 0mA to 90mA
-8V ±5%
Output Voltage VOUT
VIN = 5V, IOUT = 0mA to 150mA
-8V ±5%
Maximum Output Current
Vin = 3V
90mA
Maximum Output Current
Vin = 5V
150mA
Typical Output Ripple VOUT
VIN = 3.6V, IOUT = 100mA
10mVP–P
Typical Efficiency
VIN = 3.6V, Vout = [email protected]
70%
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 912
BOOST AND INVERTING DC/DC CONVERTERS
QUICK START PROCEDURE
Demonstration circuit 912 is easy to set up to evaluate the performance of the LT3487EDD. 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 Vin or Vout and GND terminals. See Figure
2 for proper scope probe technique.
1.
Place jumpers in the following positions:
JP1
On
2.
With power off, connect the input power supply to
Vin and GND.
3.
Turn on the power at the input.
4.
Check for the proper output voltages.
NOTE: If there is no output, temporarily disconnect
the load to make sure that the load is not set too
high.
5.
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.
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 912
BOOST AND INVERTING DC/DC CONVERTERS
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 912
BOOST AND INVERTING DC/DC CONVERTERS
4
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