LM3423MHBKBSTEV/NOPB National Semiconductor, LM3423MHBKBSTEV/NOPB Datasheet - Page 27

• Manufacturer Part Number: LM3423MHBKBSTEV/NOPB
• Description: BOARD EVAL BUCK BOOST LM3423
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3423MHBKBSTEV/NOPB

• Current - Output / Channel: 1A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 35V
• Features: Dimmable
• Voltage - Input: 4.5 ~ 35V
• Utilized Ic / Part: LM3423
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM3423MHBKBSTEV

The current rating should be at least 10% higher than the
maximum average diode current (I
Buck
Boost and Buck-boost
Replace D
average diode current (I
(V
11. OUTPUT OVLO
For boost and buck-boost regulators, output OVLO is pro-
grammed with the turn-off threshold voltage (V
the desired hysteresis (V
To set V
Boost
Buck-boost
A small filter capacitor (C
the OVP pin to ground to reduce coupled switching noise.
12. INPUT UVLO
For all topologies, input UVLO is programmed with the turn-
on threshold voltage (V
(V
Method #1: If no PWM dimming is required, a two resistor
network can be used. To set V
FD
HYS
), solve for the nominal power dissipation (P
).
TURN-OFF
MAX
with D in the I
, solve for R
D
TURN-ON
). Given a diode with forward voltage
HYSO
OVP
OV1
= 47 pF) should be added from
D-MAX
). To set V
HYS
) and the desired hysteresis
:
, solve for R
D-MAX
equation to solve for the
):
HYSO
, solve for R
UV2
TURN-OFF
D
:
):
) and
OV2
:
27
To set V
Method #2: If PWM dimming is required, a three resistor net-
work is suggested. To set V
and solve for R
R
13. PWM DIMMING METHOD
PWM dimming can be performed several ways:
Method #1: Connect the dimming MosFET (Q
to the nDIM pin and the source to AGND. Apply an external
PWM signal to the gate of Q
necessary to properly turn off Q
Method #2: Connect the anode of a Schottky diode to the
nDIM pin. Apply an external inverted PWM signal to the cath-
ode of the same diode.
The DDRV pin should be connected to the gate of the dimFET
with or without level-shifting circuitry as described in the PWM
Dimming section. The dimFET should be rated to handle the
average LED current and the nominal output voltage.
14. ANALOG DIMMING METHOD
Analog dimming can be performed several ways:
Method #1: Place a potentiometer in series with the R
resistor to dim the LED current from the nominal I
zero.
Method #2: Connect a controlled current source as detailed
in the Analog Dimming section to the CSH pin. Increasing the
current sourced into the CSH node will decrease the LEDs
from the nominal I
the thermal foldback circuit.
UVH
:
TURN-ON
UV1
, solve for R
LED
as in Method #1. To set V
to zero current in the same manner as
UV1
DIM
TURN-ON
:
. A pull down resistor may be
3
.
, assume R
3
) with the drain
HYS
UV2
www.national.com
LED
, solve for
= 10 kΩ
to near
CSH