Rainbow Electronics MAX16834 - Manual (Page 13)

MAX16834
High-Power LED Driver with Integrated High-Side LED
Current Sense and PWM Dimming MOSFET Driver
______________________________________________________________________________________ 13
ESR and the bulk capacitance are equal, allowing 50%
of the ripple for the bulk capacitance. The capacitance
is given by:
where I LED is in amperes, C OUT is in farads, f SW is in
hertz, and
∆V
OUTRIPPLE is in volts. The remaining 50%
of allowable ripple is for the ESR of the output capaci-
tor. Based on this, the ESR of the output capacitor is
given by:
where IL P is the peak inductor current in amperes.
Use the below equation to calculate the RMS current
rating of the output capacitor:
Input Capacitor
The input filter capacitor bypasses the ripple current
drawn by the converter and reduces the amplitude of
high-frequency current conducted to the input supply.
The ESR, ESL, and the bulk capacitance of the input
capacitor contribute to the input ripple. Use a low-ESR
input capacitor that can handle the maximum input
RMS ripple current from the converter.
For the boost configuration, the input current is the
same as the inductor current. For buck-boost
I
(IL (1 D )) D
IL
COUT(RMS)
AVG MAX
2
MAX
A
=
Ч Ч
+
-
(
V VG
Ч Ч
D D
MAX MAX
) ( )
2
1 -
ESR
V
IL
COUT
OUTRIPPLE
P
<
×
∆ Ω
( )
( ) 2
C
I D
V f
OUT
LED MAX
OUTRIPPLE SW
≥
Ч Ч
Ч
2
∆
V IN
LV
NDRV
Q1
ON
OFF
CS
C1
PWMDIM
SGND
D1
R10 R8
MAX16834
HV
DIMOUT
SENSE+
OVP+
CLV
COMP
PGND
V IN
UVEN
SC
RT/SYNC
C2
IN
L1
V CC
C5
REF
C4
R3
REFI
R5
R6
R2
R1
R9
R4
C7
R7
FLT
Q2
C6
LED+
LEDs
LED-
C3
Figure 3. Buck-Boost LED Driver (V LED+ < 28V)