DC1267A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1267A
STEP-UP DC/DC REGULATOR
LTC3125EDCB
DESCRIPTION
Demonstration circuit 1267A is a step-up DC/DC
regulator featuring the LTC3125EDCB and is ideally suited for pulsed load applications where the
input current needs to be limited. Demonstration
circuit 1267A is configured for 500mA maximum
input current limit and can handle pulsed load currents of up to 2A, with duty cycles of up to 15%.
The input voltage range is 3.3V ±10%.
The package style for the LTC3125EDCB is an 8
lead 3mm x 2mm plastic DFN. The fixed input curTable 1.
rent limit can be adjusted by replacing one resistor.
The LTC3125 datasheet gives a complete description of the part, operation and application information and must be read in conjunction with this
quick start guide for demo circuit 1267A.
Design files for this circuit board are available.
Call the LTC factory.
Burst Mode is a trademark of Linear Technology Corporation
Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
Input Voltage Range
3.0V – 3.6V
Input Current Limit
500mA ± 5%
Output Voltage VOUT
Output Current IOUT
Efficiency (Figure 4)
VIN = 3.0V to 3.6V, IIN = 0A to 500mA
4.0V ± 4%
VIN = 3.0V, IIN = 500mA
≥ 300mA
VIN = 3.6V, IIN = 500mA
≥ 400mA
VIN = 3.0V, IOUT = 300mA
89.8% typical
VIN = 3.6V, IOUT = 400mA
91.4% typical
QUICK START PROCEDURE
Demonstration circuit 1267A is easy to set up to
evaluate the performance of the LTC3125EDCB.
Refer to Figure 1 for proper measurement equipment setup and follow the procedure below:
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
or directly across the capacitor. See Figure 2 for
proper scope probe technique.
2.
With power off, connect the input power supply
to Vin and GND.
3.
Turn on the power at the input.
NOTE: Make
NOTE: When
1.
Place the jumper in the following position:
JP1
On
sure that the input voltage does not
exceed 4V.
4.
Check for the proper output voltage.
Vout = 3.84V to 4.16V,
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 voltage is established,
adjust the load within the operating range and
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1267A
STEP-UP DC/DC REGULATOR
observe the output voltage regulation, ripple
voltage, efficiency and other parameters.
-
Vout Load
6.
+
Vout
-
+
V
The method for evaluating pulsed loads will be
discussed in the next section.
A
Iout
Optional Circuit for Pulsed Loads
Pulse Generator
0-5V +
BNC cable to scope
10mV/A
-
+
Iin
A
+
V
Vin
Vin supply
-
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple Directly Across Bulk Capacitor
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1267A
STEP-UP DC/DC REGULATOR
PULSED LOAD TESTING
Demonstration circuit 1267A can be setup for
simple evaluation of pulse loads – please see
optional circuit in Figure 1 for proper setup. The
circuit is capable of pulsed load of up to 2A with
duty cycles up to 15%. Starting from step 5 in
the quick start procedure above, follow the procedure below:
4.
A pulse generator with adjustable amplitude is
connected between IOSTEP_CLK and GND
as indicated in Figure 1. The pulse generator
should be capable of generating up to 5V
pulses. Adjust the period and duty cycle of this
signal to match that of the required load prior
to attaching the pulse generator.
1.
Disconnect all loads from Vout as the pulse
load circuitry is on board.
5.
2.
The pulsed load current is measured by connecting IOSTEP to the scope using a BNC
cable and setting the oscilloscope to 10mV/div
Adjust pulse generator amplitude until the required load current is achieved as measured
on IOSTEP (10mV/A).
6.
An example result showing Vout, Iin and a
pulse load Iout is given in Figure 3.
3.
Input current and output voltage can be
measured on an oscilloscope for evaluation.
Vout (100mV/div AC coupled)
Iin (200mA/div)
Iout (2A/div)
(IOSTEP at 20mV/div)
th
Figure 3. Pulse Load Waveforms for 2A pulsed load, 1/8 duty cycle, 4.6ms period
ADJUSTING INPUT CURRENT LIMIT
It is possible to modify the demonstration circuit for either higher or lower input current limits. This is accomplished by changing resistor RLMT to the required value as suggested in the LTC3125 datasheet.
Note that for these different current values, the inductor may have to be changed. Please refer to the datasheet for more information.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1267A
STEP-UP DC/DC REGULATOR
500mA input
current limit
Figure 4. Typical Efficiency vs. Load Current
4
E1
E2
[1]
68uF
6.3V
+ C1
10uF
6.3V
CIN1
10uF
6.3V
CIN2
[1]
OFF
ON
1
RUN 3
FOR DEMO BOARD USE ONLY.
NOTES: UNLESS OTHERWISE SPECIFIED,
GND
UP TO
500mA
3V - 3.6V
VIN
U1
1%
RLMT
44.2K
JP1
2
3
6
4
5
PROG
SHDN
VIN
CS
1.5uH
8
FB
VOUT
SW
LTC3125EDCB
L1
1
9
GND
GND
2
7
OPT
CP
OPT
CFF
432K
1%
R5
1M
1%
R4
10uF
6.3V
CO5
2
+
2200uF
6.3V
+
51
R2
2200uF
6.3V
CO2
+
1
2200uF
6.3V
CO3
10K
R1
SUD50N03-10CP
1
0.01
R3
CO1
3
J1
TP1
+
E5
OPT
6.3V
CO4
GND
+
E3
GND
PULSE LOAD
E4
22mF
OPT
VOUT
CO6 4.0V / 2A
IOSTEP
10mV / A
IOSTEP_CLK
DYNAMIC LOAD CIRCUIT
2
3
4
5
Q1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1267A
STEP-UP DC/DC REGULATOR
5
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