Datasheet
V
CC
1
EN
V
IN
OVP
RCT
FLT DPOL
DDRV
HSP
AGND
COMP
CSH
DAP
RPD
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
nDIM
TIMR
LRDY
PGND
GATE
HSN
IS
21
V
IN
OVP
RCT
AGND
COMP
CSH
nDIM
V
CC
1
EN
DDRV
HSP
DAP
RPD
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
PGND
GATE
HSN
IS
17
V
IN
(V)
EFFICIENCY (%)
100
95
90
85
80
10 15 20 25 30
LM3421, LM3421-Q1
LM3423, LM3423-Q1
SNVS574E –JULY 2008–REVISED MAY 2013
www.ti.com
Figure 1. Boost Evaluation Board
9 Series LEDs at 1A
Connection Diagrams
Top View Top View
Figure 2. 16-Lead TSSOP Figure 3. 20-Lead TSSOP
Package Number PWP Package Number PWP
PIN DESCRIPTIONS
LM3423 LM3421 Name Description Function
Bypass with 100 nF capacitor to AGND as close to the device as
1 1 V
IN
Input Voltage
possible in the circuit board layout.
Connect to AGND for zero current shutdown or apply > 2.4V to
2 2 EN Enable
enable device.
3 3 COMP Compensation Connect a capacitor to AGND to set the compensation.
Connect a resistor to AGND to set the signal current. For analog
4 4 CSH Current Sense High dimming, connect a controlled current source or a potentiometer to
AGND as detailed in the ANALOG DIMMING section.
External RC network sets the predictive “off-time” and thus the
5 5 RCT Resistor Capacitor Timing
switching frequency.
Connect to PGND through the DAP copper pad to provide ground
6 6 AGND Analog Ground
return for CSH, COMP, RCT, and TIMR.
Connect to a resistor divider from V
O
to program output over-voltage
7 7 OVP Over-Voltage Protection lockout (OVLO). Turn-off threshold is 1.24V and hysteresis for turn-on
is provided by 23 µA current source.
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Product Folder Links: LM3421 LM3421-Q1 LM3423 LM3423-Q1