Texas Instruments Emulated Peak Current Mode Buck Controller for Low Output Voltage LM3495EVAL/NOPB LM3495EVAL/NOPB Datenbogen
Produktcode
LM3495EVAL/NOPB
S
S
S
G
D
D
D
D
SO-8
TI Confidential - NDA Restrictions
Testing The Converter
5
Testing The Converter
shows a block diagram of connections for making measurements of efficiency. The wires used for
making connections at both the input and output should be rated to at least 10A of continuous current and
should be no longer than is needed for convenient testing. A series ammeter capable of measuring 10A or
more should be used for both the input and the output lines. Dedicated voltmeters should be connected
with their positive and negative leads right at the four power terminals at the top of the evaluation board.
This measurement technique minimizes the voltage loss in the wires that connect the evaluation board to
the input power supply and the electronic load.
should be no longer than is needed for convenient testing. A series ammeter capable of measuring 10A or
more should be used for both the input and the output lines. Dedicated voltmeters should be connected
with their positive and negative leads right at the four power terminals at the top of the evaluation board.
This measurement technique minimizes the voltage loss in the wires that connect the evaluation board to
the input power supply and the electronic load.
Output voltage ripple measurements should be taken directly across the 100 nF ceramic capacitor Cox,
placed right between the output terminals. Care must be taken to minimize the loop area between the
oscilloscope probe tip and the ground lead. One method to minimize this loop is to remove the probe’s
spring tip and ‘pigtail’ ground lead and then wind bare wire around the probe shaft. The bare wire should
contact the ground of the probe, and the end of the wire can then contact the ground side of Cox.
placed right between the output terminals. Care must be taken to minimize the loop area between the
oscilloscope probe tip and the ground lead. One method to minimize this loop is to remove the probe’s
spring tip and ‘pigtail’ ground lead and then wind bare wire around the probe shaft. The bare wire should
contact the ground of the probe, and the end of the wire can then contact the ground side of Cox.
shows a diagram of this method.
An oscilloscope probe modified as described above can also be used to measure the switch node voltage,
LG pin voltage, and HG pin voltage (all three with respect to ground) using the 40mil diameter hole pairs
labeled “+ SW –“, “+ LG –“, and “+ HG –“, respectively.
LG pin voltage, and HG pin voltage (all three with respect to ground) using the 40mil diameter hole pairs
labeled “+ SW –“, “+ LG –“, and “+ HG –“, respectively.
6
SKIP/PWM
A second SPDT switch labeled SKIP/FPWM determines that control scheme the LM3495 uses at low
output currents. When set to SKIP, the converter saves energy during light loads (approximately 100 mA
or less) by using the body diode of the low side FET, as well as leaving the high side FET off if possible.
When the switch is set to FPWM, the LM3495 forces both top and bottom FETs to switch during every
cycle, regardless of the load current.
output currents. When set to SKIP, the converter saves energy during light loads (approximately 100 mA
or less) by using the body diode of the low side FET, as well as leaving the high side FET off if possible.
When the switch is set to FPWM, the LM3495 forces both top and bottom FETs to switch during every
cycle, regardless of the load current.
7
MOSFET Footprints
The LM3495 evaluation board has footprints for single N-MOSFETs with SO-8 packages and standard
pinouts. These footprints can also accept newer MOSFET packages that are compatible with SO-8
footprints. see
pinouts. These footprints can also accept newer MOSFET packages that are compatible with SO-8
footprints. see
. Q1 is the high side FET, and Q2 low side FET.
Figure 2. SO-8 MOSFET Pinout
8
Permanent Components
The following components should remain the same for any new circuits evaluated on the LM3495
evaluation board:
evaluation board:
Name
Value
Cb
0.1 µF
Cf
1 µF
Cdd
2.2 µF
2
AN-1446 LM3495 Evaluation Board
SNVA149B – March 2006 – Revised April 2013
Copyright © 2006–2013, Texas Instruments Incorporated