Datasheet

V
IN
= 4.5V ± 25V
V
OUT
= +3.3V
I
OUT
= 3A
C1
22 éF
C9
150 éF
R6
10 k:
R5
30.9 k:
J1
J2
ENABLE
GND
R1
10 k:
C8
1500 pF
C2
4.7 éF
R4
348:
J3
J4
PGOOD
J6
J5
C5
1 éF
D1
R2
Open
R7
15 k:
C4
0.1 éF
C3
4.7 éF
LM20333
FB
AGND
SW
GND
GND
GND
U1
14
11
12
2
10
9
SW
13
SW
8
SW
7
BOOT
17
VIN
16
VIN
15
VIN
6
VIN
5
EP
COMP
4
SS
1
SYNC
20
PGOOD
3
EN
19
VCC
18
C7
10 pF
R3
Open
L1
SYNC
J10
GND
J8
C6
100 nF
SS/TRK
J7
J9
TP1
VPULLUP
V
OUT
10 éH
Evaluation Board Schematic www.ti.com
2 Evaluation Board Schematic
3 Powering and Loading Considerations
Read this entire page prior to attempting to power the evaluation board.
3.1 Quick Setup Procedure
1. Set the input source current limit to 3A. Turn off the input source. Connect the positive output of the
input source to J1 and the negative output to J2.
2. Connect the load, with 3A capability, to J3 for the positive connection and J4 for the negative
connection.
3. Leave the ENABLE pin, J5, open for normal operation.
4. Set the input source voltage to 12V and the load to 0.1A. The load voltage should be in regulation with
a nominal 3.3V output.
5. Slowly increase the load while monitoring the load voltage at J3 and J4. It should remain in regulation
with a nominal 3.3V output as the load is increased up to 3 Amp.
6. Slowly sweep the input source voltage from 4.5V to 25V. The load voltage should remain in regulation
with a nominal 3.3V output. If desired the output of the device can be disabled by connecting the
ENABLE pin (J5) to GND (J8).
7. Select the pull-up voltage for PGOOD by using the JP1 shunt to connect VPULLUP to VOUT or VCC.
8. The frequency of operation can be varied as desired by connecting a signal .
2
AN-1791 LM20333 Evaluation Board SNVA325B–May 2008–Revised May 2013
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