MAX16821A Datasheet, PDF (17/25 Pages) Maxim Integrated Products – High-Power Synchronous HBLED Drivers with Rapid Current Pulsing

High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
High-Side Buck Driver
with Synchronous Rectification
In Figure 9, the input voltage goes from 7V to 28V, the LED
load is connected from the positive side to the current-
sense resistor (R1) in series with the inductor, and MODE
is connected to V_CC. For the inner average current-loop
inductor, current is sensed by resistor R1 and is then
transferred to the low side by the high-side current-sense
amplifier, U2. The voltage appearing across resistor R11
becomes the average inductor current-sense voltage for
the inner average current loop. To regulate the LED
current, R2 creates a voltage that the differential ampli-
fier compares to its internal reference. Capacitor C1 is
small and is added to reduce the ripple current in the
LEDs. In cases where the LEDs can tolerate a higher
ripple current, capacitor C1 can be omitted.
C11
C10 _R8
R7
C9
C8
R6
V_CC
R4
C3
R3
ON/OFF
14
I.C.
15 OVI
I.C.
16 CLP
13
12
11
OUTV RT/SYNC EN
10
9
MODE CLKOUT
8
SGND
N.C. 7
DH 6
17 EAOUT
18 EAN
19 DIFF
MAX16821A
MAX16821B
MAX16821C
LX 5
BST 4
DL 3
V_IN
7V TO 28V
C2
Q1
L1
R5
C4
D1
Q2
20 CSN
N.C. 2
21 CSP
SGND SENSE- SENSE+ SGND
IN
22
23
24
25
26
V_IN
PGND 1
V_CC
V_DD
27
28
LED
STRING
C1
R1
V_CC
RS+
U2
RS- OUT
R2
R11
C7
C6
C5
Figure 9. Application Circuit for a High-Side Buck LED Driver
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