MAX16821A Datasheet, PDF (21/25 Pages) Maxim Integrated Products – High-Power Synchronous HBLED Drivers with Rapid Current Pulsing

High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
V_CC
R10
PWM DIM
Q4
PWM DIM
V_CC
V_LED
R8
Q5
R9
R4
C3
R3
ON/OFF
C11
C10 _R7
R6
C9
C8
Q3
R5
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
BST 4
DL 3
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
V_IN
7V TO 28V
C2
L1
D1
V_LED
Q1
C1
LED
STRING
PWM DIM
Q2
R2
R1
C7
C6
C5
Figure 11. Boost LED Driver with PWM Dimming
Power Dissipation
Calculate power dissipation in the MAX16821A/
MAX16821B/MAX16821C as a product of the input volt-
age and the total V_CC regulator output current (I_CC).
I_CC includes quiescent current (I_Q) and gate-drive cur-
rent (I_DD):
P_D = V_IN x I_CC
I_CC = I_Q + [f_SW x (Q_G1 + Q_G2)]
where Q_G1 and Q_G2 are the total gate charge of the
low-side and high-side external MOSFETs at V_GATE =
5V, I_Q is the supply current, and f_SW is the switching
frequency of the LED driver.
Use the following equation to calculate the maximum
power dissipation (P_DMAX) in the chip at a given ambi-
ent temperature (T_A):
P_DMAX = 34.5 x (150 – T_A) mW
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