High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
Boost:
For adequate phase margin at crossover, place the zero
R CF ≤
V RAMP × f SW × L
A V × R S × ( V LED ? V IN ) × g m
formed by R CF and C CZ at least 3 to 5 times below the
crossover frequency. The pole formed by R CF and C CP
is added to eliminate noise spikes riding on the current
waveform and is placed at the switching frequency.
The crossover frequency of the inner current loop is
given by:
PWM Dimming
Even though the MAX16821A/MAX16821B/MAX16821C
f C =
R S
V RAMP
×
V LED
2 × π × L
× 34 . 5 × g m × R CF
do not have a separate PWM input, PWM dimming can
be easily achieved by means of simple external circuitry.
See Figures 10 and 11.
V CC
V LED
R9
R3
C3
R4
ON/OFF
R10
C11
14
I.C.
13
OUTV
12
RT/SYNC
11
EN
10
MODE
9
CLKOUT
8
SGND
V IN
7V TO 28V
C10
R9
15 OVI
16 CLP
N.C. 7
DH 6
Q1
C2
R7
17 EAOUT
LX 5
L1
V LED
C9
C8
R6
18 EAN
MAX16821A
MAX16821B
MAX16821C
BST 4
R5
C4
PWM DIM
LED
STRING
19 DIFF
20 CSN
DL 3
N.C. 2
D2
Q2
Q3
R2
R1
21 CSP
PGND 1
SGND
22
SENSE-
23
SENSE+
24
SGND
25
IN
26
V CC
27
V DD
28
V IN
Figure 10. Low-Side Buck LED Driver with PWM Dimming
C7
C6
C5
20
______________________________________________________________________________________
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MAX16822AASA/V+T 功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
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