LM3429MH National Semiconductor, LM3429MH Datasheet - Page 19

• Manufacturer Part Number: LM3429MH
• Description: IC, LED DRIVER, CNTRL, 14TSSOP
• Manufacturer: National Semiconductor

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

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
www.national.com
) from the