LM3421_09 Datasheet, PDF (3/24 Pages) National Semiconductor (TI) – N-Channel Controllers for Constant Current LED Drivers

LM3423
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LM3421
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11
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14
10
15
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16
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17
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18
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19
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20
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EP (21)
EP (17)
Name
TIMR
LRDY
DPOL
DDRV
PGND
GATE
V_CC
IS
RPD
HSP
HSN
EP
Function
Fault Timer: The fault timer is comprised of an external capacitor, an internal charging current
source, an internal discharge N-channel MOSFET, and a comparator that latches the fault
condition when the threshold voltage (1.24V) is exceeded.
LED Ready status flag: This is an N-channel MOSFET open drain output which pulls down
whenever the LED current is not in regulation.
Dim Polarity: Selects the polarity of the DIM driver output. Tie to V_CC or leave open for low
side dimming, tie to ground for high side dimming.
External Dimming MOSFET Gate Drive: Gate driver output responding to nDIM input.
Power Ground: GATE and DDRV gate drive ground current return pin. This pin should be
connected via the circuit board to the AGND pin through the EP copper circuit board pad.
Main switching MOSFET gate drive output.
Internal Regulator Bypass: 6.9V low dropout linear regulator output. Bypass with a 2.2µF–
3.3µF, ceramic type capacitor to PGND.
Main Switch Current Sense input: This pin is used for current mode control and cycle-by-cycle
current limit. This pin can be tied to the drain of the main N-channel MOSFET switch for
R_DS(ON) sensing or tied to a sense resistor installed in the source of the same device.
Resistor Pull-Down: This is an open drain N-channel MOSFET which is used to pull-down the
low side of all external resistor dividers (V_IN UVLO, OVP). This pin allows for system “zero-
current” shutdown.
High Side Sense Positive: LED current sense positive input. An external resistor sets a
reference current flowing into this pin from the programmed high-side sense voltage. Although
the current into this pin can be set to values ranging from 10µA through 1mA, a value of 100µA
is recommended. This pin is a virtual ground whose potential is set by the voltage on the HSN
pin.
High Side Sense Negative: This pin sets the reference voltage for the HSP input. An external
resistor of the same value as that used on the HSP pin should be connected from this pin to
the negative side of the current sense resistor.
EP: Star ground, connecting AGND and PGND. For thermal considerations please refer to
(Note 4) of the Electrical Characteristics table.
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