LM3423

LM3421

Name

Function

10

-

TIMR

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.

11

-

LRDY

LED Ready status flag: This is an N-channel MOSFET open drain output which pulls down

whenever the LED current is not in regulation.

12

-

DPOL

Dim Polarity: Selects the polarity of the DIM driver output. Tie to V

side dimming, tie to ground for high side dimming.

13

9

DDRV

External Dimming MOSFET Gate Drive: Gate driver output responding to nDIM input.

14

10

PGND

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.

15

11

GATE

Main switching MOSFET gate drive output.

16

12

V

CC

Internal Regulator Bypass: 6.9V low dropout linear regulator output. Bypass with a 2.2µF–

3.3µF, ceramic type capacitor to PGND.

17

13

IS

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

18

14

RPD

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

current” shutdown.

19

15

HSP

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.

20

16

HSN

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 (21)

EP (17)

EP

EP: Star ground, connecting AGND and PGND. For thermal considerations please refer to

(Note 4) of the Electrical Characteristics table.

3

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