LM3421MH/NOPB National Semiconductor, LM3421MH/NOPB Datasheet - Page 30

• Manufacturer Part Number: LM3421MH/NOPB
• Description: IC LED DRVR HP CONS CURR 16TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: High Power, Constant Currentr

Specifications of LM3421MH/NOPB

• Constant Current: Yes
• Topology: PWM, SEPIC, Step-Down (Buck), Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: No
• Type - Primary: Automotive
• Type - Secondary: High Brightness LED (HBLED)
• Frequency: 2MHz
• Voltage - Supply: 4.5 V ~ 75 V
• Voltage - Output: 3 V ~ 72 V
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 1A
• Internal Switch(s): No
• Efficiency: 95%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM3421MH/NOPB; LM3421MH

www.national.com
6. PEAK CURRENT LIMIT
Solve for R
The closest standard resistor is 0.04 Ω therefore I
The chosen component from step 6 is:
7. LOOP COMPENSATION
ω
ω
T
To ensure stability, calculate ω
Solve for C
To attenuate switching noise, calculate ω
Assume R
The chosen components from step 7 are:
U0
P1
Z1
is approximated:
is approximated:
is approximated:
FS
LIM
CMP
= 10Ω and solve for C
:
:
P2
:
FS
:
P3
:
LIM
is:
30
8. INPUT CAPACITANCE
Solve for the minimum C
To minimize power supply interaction a 200% larger capaci-
tance of approximately 20 µF is used, therefore the actual
Δv
selection is limited, four 4.7 µF X7R capacitors are chosen.
Determine minimum allowable RMS current rating:
The chosen components from step 8 are:
9. NFET
Determine minimum Q1 voltage rating and current rating:
A 100V NFET is chosen with a current rating of 32A due to
the low R
The chosen component from step 9 is:
10. DIODE
Determine minimum D1 voltage rating and current rating:
A 100V diode is chosen with a current rating of 12A and V
600 mV. Determine P
IN-PP
is much lower. Since high voltage ceramic capacitor
DS-ON
= 50 mΩ. Determine I
D
:
IN
:
T-RMS
and P
T
:
D
=