Texas Instruments LM34919BEVAL Wide Vin Constant On-Time Buck Switching Regulator Evaluation Module LM34919BEVAL/NOPB LM34919BEVAL/NOPB Datenbogen
Produktcode
LM34919BEVAL/NOPB
FB
SW
BST
VCC
ISEN
SGND
VIN
R1
28k
SS
RTN
Gnd
D1
A1
A2
On
Timer
Minimum
Off
Timer
Logic
Regulation
Comparator
B3
A3
Current Limit
Detect
D3
C3
0.27
:
C1
IN
Gnd
C2
1
P
F
RON/SD
C6
0.022
P
F
0.1
P
F
C3
1
P
F
0.1
P
F
C4
B1
V
IN
V
OUT
C5
D1
D2
C1
2.49k
R3
R2
P
F
10
P
F
10
3.3V
LM34919B
R6 0
:
C8
C7
2.5V
0.022
P
F
R4
6V to 24V
L1 8.2
P
H
787
:
Board Layout and Probing
3
Board Layout and Probing
The pictorial in
shows the placement of the circuit components. The following should be kept in
mind when the board is powered:
•
The LM34919B, and diode D1 may be hot to the touch when operating at high input voltage and high
load current.
load current.
•
Use CAUTION when probing the circuit at high input voltages to prevent injury, as well as possible
damage to the circuit.
damage to the circuit.
•
At maximum load current (0.6A), the wire size and length used to connect the load becomes important.
Ensure there is not a significant drop in the wires between this evaluation board and the load.
Ensure there is not a significant drop in the wires between this evaluation board and the load.
4
Board Connection/Start-up
The input connections are made to the J1 connector. The load is connected to the J2 (OUT) and J3
(GND) terminals. Ensure the wires are adequately sized for the intended load current. Before start-up a
voltmeter should be connected to the input terminals, and to the output terminals. The load current should
be monitored with an ammeter or a current probe. It is recommended that the input voltage be increased
gradually to 6V, at which time the output voltage should be 3.3V. If the output voltage is correct with 6V at
V
(GND) terminals. Ensure the wires are adequately sized for the intended load current. Before start-up a
voltmeter should be connected to the input terminals, and to the output terminals. The load current should
be monitored with an ammeter or a current probe. It is recommended that the input voltage be increased
gradually to 6V, at which time the output voltage should be 3.3V. If the output voltage is correct with 6V at
V
IN
, then increase the input voltage as desired and proceed with evaluating the circuit. DO NOT EXCEED
40V AT V
IN
.
5
Output Ripple Control
The LM34919B requires a minimum of 25 mVp-p ripple at the FB pin, in phase with the switching
waveform at the SW pin, for proper operation. The required ripple can be supplied from ripple at V
waveform at the SW pin, for proper operation. The required ripple can be supplied from ripple at V
OUT
,
through the feedback resistors as described in
and
, or the ripple can be generated
separately (using R5, C9, and C10) in order to keep the ripple at V
OUT
at a minimum (
5.1
Option A) Lowest Cost Configuration
This evaluation board is supplied with R4 installed in series with the output capacitance (C7, C8). R4 is
chosen to generate
chosen to generate
≥
25 mVp-p at V
OUT
, knowing that the minimum ripple current in this circuit is
≊
140
mAp-p at minimum V
IN
. Using 0.27
Ω
for R4, the ripple at V
OUT
ranges from
≊
37 mVp-p to
≊
88 mVp-p over
the input voltage range. If the application can accept this ripple level, this is the most economical solution.
The circuit is shown in
The circuit is shown in
. See
.
Figure 2. Lowest Cost Configuration
3
SNVA418A – May 2010 – Revised April 2013
AN-2016 LM34919B Evaluation Board
Copyright © 2010–2013, Texas Instruments Incorporated