Datasheet

IS
AGND
PWM
Start new on time
nDIM
COMP
REFERENCE
CURRENT
LIMIT
CSH
HSN
LOGIC
HSP
EN
OVP
HYSTERESIS
LED CURRENT LOW
S
R
Q
UVLO
DDRV
GATE
PGND
OVP
LRDY
RPD
EN
LatchOff
TIMR
OVLO
FLT
LED CURRENT HIGH
Regulator
Thermal
Limit
TLIM
TLIM
OVLO
PGND
LatchOff
Standby
Dimming
Reset
Dominant
RCT
800 mV
STOP
820k
500k
LEB
In the LM3421, TIMR is internally shorted to AGND.
1.235V
6.9V LDO
(4.1V)
DPOL
Grey pins are available in the LM3423 only.
LEB
W = 150 ns
V
IN
/25
V
IN
UVLO
HYSTERESIS
1.24V
V
CC
1.235V
V
CC
1.24V
1.24V
0.245V
1.0V
1.6V
V
CC
UVLO
V
CC
V
CC
UVLO
V
IN
23 PA
23 PA
11.5 PA
LM3421, LM3421-Q1
LM3423, LM3423-Q1
SNVS574E –JULY 2008–REVISED MAY 2013 www.ti.com
BLOCK DIAGRAM
THEORY OF OPERATION
The LM3421/23 are N-channel MosFET (NFET) controllers for buck, boost and buck-boost current regulators
which are ideal for driving LED loads. The controller has wide input voltage range allowing for regulation of a
variety of LED loads. The high-side differential current sense, with low adjustable threshold voltage, provides an
excellent method for regulating output current while maintaining high system efficiency. The LM3421/23 uses a
Predictive Off-time (PRO) control architecture that allows the regulator to be operated using minimal external
control loop compensation, while providing an inherent cycle-by-cycle current limit. The adjustable current sense
threshold provides the capability to amplitude (analog) dim the LED current and the output enable/disable
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