LM3429MH National Semiconductor, LM3429MH Datasheet - Page 19
LM3429MH
Manufacturer Part Number
LM3429MH
Description
IC, LED DRIVER, CNTRL, 14TSSOP
Manufacturer
National Semiconductor
Datasheet
1.LM3429MHNOPB.pdf
(34 pages)
Specifications of LM3429MH
Led Driver Application
Automotive, General Illumination
No. Of Outputs
1
Output Current
1A
Input Voltage
4.5V To 75V
Dimming Control Type
Analogue / PWM
Topology
Boost, Buck, Buck-Boost, SEPIC
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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Manufacturer
Quantity
Price
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Manufacturer:
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Quantity:
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Part Number:
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Manufacturer:
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Quantity:
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Part Number:
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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