MAX16821A_10 Datasheet, PDF (16/24 Pages) Maxim Integrated Products – High-Power Synchronous HBLED Drivers with Rapid Current Pulsing

High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
Low-Side Buck Driver
with Synchronous Rectification
In Figure 8, the input voltage goes from 7V to 28V and,
because of the ground-based current-sense resistor,
the output voltage can be as high as the input. The syn-
chronous MOSFET keeps the power dissipation to a
minimum, especially when the input voltage is large
compared to the voltage on the LED string. For the
inner average current-loop inductor, current is sensed
by resistor R1. To regulate the LED current, R2 creates
a voltage that the differential amplifier compares to
0.6V. Capacitor C1 is small and helps reduce the ripple
current in the LEDs. Omit C1 in cases where the LEDs
can tolerate a higher ripple current. The average current-
mode control scheme converts the input voltage to a
current source feeding the LED string.
V_LED
R9
R10
C11
C10 _R9
R7
C9
C8
R6
V_CC
R4
C3
R3
ON/OFF
14
I.C.
15 OVI
13
12
11
OUTV RT/SYNC EN
10
MODE
9
CLKOUT
8
SGND
N.C. 7
16 CLP
DH 6
17 EAOUT
18 EAN
19 DIFF
MAX16821A
MAX16821B
MAX16821C
LX 5
R5
BST 4
DL 3
20 CSN
N.C. 2
21 CSP
PGND 1
SGND SENSE- SENSE+ SGND
IN
V_CC
V_DD
22
23
24
25
26
27
28
V_IN
V_IN
7V TO 28V
C2
Q1
V_LED
L1
C4
Q2
C1
LED
STRING
D2
R2
R1
C7
C6
C5
Figure 8. Application Circuit for a Low-Side Buck LED Driver
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