MAX16821A Datasheet, PDF (22/25 Pages) Maxim Integrated Products – High-Power Synchronous HBLED Drivers with Rapid Current Pulsing

High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
PCB Layout
Use the following guidelines to layout the LED driver.
1) Place the IN, V_CC, and V_DD bypass capacitors
close to the MAX16821A/MAX16821B/MAX16821C.
2) Minimize the area and length of the high-current
switching loops.
3) Place the necessary Schottky diodes that are con-
nected across the switching MOSFETs very close to
the respective MOSFET.
4) Use separate ground planes on different layers of
the PCB for SGND and PGND. Connect both of
these planes together at a single point and make
this connection under the exposed pad of the
MAX16821A/MAX16821B/MAX16821C.
5) Run the current-sense lines CSP and CSN very
close to each other to minimize the loop area. Run
the sense lines SENSE+ and SENSE- close to each
other. Do not cross these critical signal lines with
power circuitry. Sense the current right at the pads
of the current-sense resistors. The current-sense
signal has a maximum amplitude of 27.5mV. To pre-
vent contamination of this signal from high dv/dt
and high di/dt components and traces, use a
ground plane layer to separate the power traces
from this signal trace.
6) Place the bank of output capacitors close to the load.
7) Distribute the power components evenly across the
board for proper heat dissipation.
8) Provide enough copper area at and around the
switching MOSFETs, inductor, and sense resistors
to aid in thermal dissipation.
9) Use 2oz or thicker copper to keep trace inductances
and resistances to a minimum. Thicker copper con-
ducts heat more effectively, thereby reducing thermal
impedance. Thin copper PCBs compromise efficiency
in applications involving high currents.
PART
MAX16821A
MAX16821B
MAX16821C
Selector Guide
DIFFERENTIAL
SET VALUE
(V_SENSE+ - V_SENSE-)
(V)
0.60
0.10
0.03
DIFFERENTIAL
AMP GAIN
(V/V)
1
6
20
Pin Configuration
TOP VIEW
21 20 19 18 17 16 15
SGND 22
SENSE- 23
SENSE+ 24
SGND 25
IN 26
V_CC 27
V_DD 28
*EP
MAX16821A
MAX16821B
MAX16821C
+
1 234567
14 I.C.
13 OUTV
12 RT/SYNC
11 EN
10 MODE
9 CLKOUT
8 SGND
*EP = EXPOSED PAD.
TQFN
PROCESS: BiCMOS
Chip Information
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