Datasheet
1
2
3
4
9
10
11
12
8
DAP
5
7
6
VOUT
SW2
PGND
SW1
PV
IN
EN
FB
VSEL
MODE/
SYNC
SGND
NC*
VDD
DAP
11
12
10
9
8
7
6
5
4
3
2
1
FB
VSEL
MODE/
SYNC
SGND
NC*
VDD
VOUT
SW2
PGND
SW1
PV
IN
EN
LM3668
www.ti.com
SNVS449M –JUNE 2007–REVISED MAY 2013
Connection Diagrams
Figure 4. Top View Figure 5. Bottom View
See Package Number DQB (WSON)
Pin Descriptions
Pin # Pin Name Description
1 VOUT Connect to output capacitor.
2 SW2 Switching Node connection to the internal PFET switch (P2) and NFET synchronous rectifier (N2).
3 PGND Power Ground.
4 SW1 Switching Node connection to the internal PFET switch (P1) and NFET synchronous rectifier (N1).
5 PV
IN
Supply to the power switch, connect to the input capacitor.
6 EN Enable Input. Set this digital input high for normal operation. For shutdown, set low.
7 VDD Signal Supply input. If board layout is not optimum an optional 1µF ceramic capacitor is suggested as close
to this pin as possible.
8 NC No connect. Connect this pin to SGND on PCB layout.
9 SGND Analog and Control Ground.
10 MODE/SYNC Mode = LOW, Automatic Mode. Mode= HI, Forced PWM Mode SYNC = external clock synchronization from
1.6MHz to 2.7MHz (When SYNC function is used, device is forced in PWM mode).
11 VSEL Voltage selection pin; (for example, 2.8V/3.3V option) Logic input low (or GND) = 2.8V and logic high = 3.3V
(or V
IN
) to set output Voltage.
12 FB Feedback Analog Input. Connect to the output at the output filter.
DAP DAP Die Attach Pad, connect the DAP to SGND on PCB layout to enhance thermal performance. It should not be
used as a primary ground connection.
Table 1. Additional Device Information
Order Number Output Voltage (V) Package Package Marking Supplied As
LM3668SD-2833/NOPB 1000 units, tape-and-reel
2.8, V
SEL
= low
S017B
3.3, V
SEL
= high
LM3668SDX-2833/NOPB 4500 units, tape-and-reel
LM3668SD-3034/NOPB 1000 units, tape-and-reel
3.0, V
SEL
= low
DQB (WSON) S018B
3.4, V
SEL
= high
LM3668SDX-3034/NOPB 4500 units, tape-and-reel
LM3668SD-4550/NOPB 1000 units, tape-and-reel
4.5, V
SEL
= low
S019B
5.0, V
SEL
= high
LM3668SDX-4550/NOPB 4500 units, tape-and-reel
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