LM3429MH/NOPB National Semiconductor, LM3429MH/NOPB Datasheet - Page 19

• Manufacturer Part Number: LM3429MH/NOPB
• Description: IC LED DRVR HP CONS CURR 14TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: High Power, Constant Currentr

Specifications of LM3429MH/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
• Mounting Type: Surface Mount
• Package / Case: 14-TSSOP Exposed Pad, 14-eTSSOP 14-HTSSOP
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 1A
• Internal Switch(s): No
• Efficiency: 95%
• For Use With: LM3429BSTEVAL - BOARD EVAL FOR BOOST LM3429LM3429BKBSTEVAL - BOARD EVAL FOR BUCK-BOOST LM3429
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Other names: LM3429MH

5. LED RIPPLE CURRENT
Set the nominal LED ripple current (Δi
the output capacitance (C
Buck
Boost and Buck-boost
To set the worst case LED ripple current, use D
solving for C
The minimum allowable RMS output capacitor current rating
(I
Buck
Boost and Buck-boost
6. PEAK CURRENT LIMIT
Set the peak current limit (I
path sense resistor (R
7. LOOP COMPENSATION
Using a simple first order peak current mode control model,
neglecting any output capacitor ESR dynamics, the neces-
sary loop compensation can be determined.
First, the uncompensated loop gain (T
be approximated:
Buck
Boost and Buck-boost
CO-RMS
) can be approximated:
O
.
LIM
):
O
):
LIM
) by solving for the transistor
U
LED-PP
) of the regulator can
), by solving for
MAX
when
19
Where the pole (ω
Buck
Boost
Buck-boost
And the RHP zero (ω
Boost
Buck-boost
And the uncompensated DC loop gain (T
Buck
Boost
Buck-boost
For all topologies, the primary method of compensation is to
place a low frequency dominant pole (ω
that there is ample phase margin at the crossover frequency.
This is accomplished by placing a capacitor (C
COMP pin to GND, which is calculated according to the lower
value of the pole and the RHP zero of the system (shown as
a minimizing function):
If analog dimming is used, C
larger to maintain stability as the LEDs are dimmed to zero.
P1
) is approximated:
Z1
) is approximated:
CMP
should be approximately 4x
P2
U0
) which will ensure
) is approximated:
CMP
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) from the