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PDF MAX16821A Data sheet ( Hoja de datos )
| Número de pieza | MAX16821A | |
| Descripción | High-Power Synchronous HBLED Drivers | |
| Fabricantes | Maxim Integrated Products | |
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19-0881; Rev 0; 7/07
High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
www.datasheet4u.com
General Description
The MAX16821A/MAX16821B/MAX16821C pulse-
width-modulation (PWM) LED driver controllers provide
high output-current capability in a compact package
with a minimum number of external components. The
MAX16821A/MAX16821B/MAX16821C are suitable for
use in synchronous and nonsynchronous step-down
(buck), boost, buck-boost, SEPIC, and Cuk LED drivers. A
logic input (MODE) allows the devices to switch between
synchronous buck and boost modes of operation. These
devices are the first high-power drivers designed specifi-
cally to accommodate common-anode HBLEDs.
The ICs offer average current-mode control that enable
the use of MOSFETs with optimal charge and on-resis-
tance figure of merit, thus minimizing the need for
external heatsinking even when delivering up to 30A of
LED current.
The differential sensing scheme provides accurate con-
trol of the LED current. The ICs operate from a 4.75V to
5.5V supply range with the internal regulator disabled
(VCC connected to IN). These devices operate from a
7V to 28V input supply voltage with the internal regula-
tor enabled.
The MAX16821A/MAX16821B/MAX16821C feature a
clock output with 180° phase delay to control a second
out-of-phase LED driver to reduce input and output fil-
ter capacitor size and to minimize ripple currents. The
wide switching frequency range (125kHz to 1.5MHz)
allows the use of small inductors and capacitors.
Additional features include programmable overvoltage
protection and an output enable function.
Applications
Front Projectors/Rear Projection TVs
Portable and Pocket Projectors
Automotive Exterior Lighting
LCD TVs and Display Backlight
Automotive Emergency Lighting and Signage
Features
♦ Up to 30A Output Current
♦ True-Differential Remote Output Sensing
♦ Average Current-Mode Control
♦ 4.75V to 5.5V or 7V to 28V Input-Voltage Range
♦ 0.1V/0.03V LED Current-Sense Options Maximize
Efficiency (MAX16821B/MAX16821C)
♦ Thermal Shutdown
♦ Nonlatching Output Overvoltage Protection
♦ Low-Side Buck Mode with or without
Synchronous Rectification
♦ High-Side Buck and Low-Side Boost Mode with or
without Synchronous Rectification
♦ 125kHz to 1.5MHz Programmable/Synchronizable
Switching Frequency
♦ Integrated 4A Gate Drivers
♦ Clock Output for 180° Out-of-Phase Operation for
Second Driver
♦ -40°C to +125°C Operating Temperature Range
Ordering Information
PART
TEMP RANGE
PIN-
PACKAGE
PKG
CODE
MAX16821AATI+ -40°C to +125°C 28 TQFN-EP* T2855-8
MAX16821BATI+ -40°C to +125°C 28 TQFN-EP* T2855-8
MAX16821CATI+ -40°C to +125°C 28 TQFN-EP* T2855-8
+Denotes a lead-free package.
*EP = Exposed pad.
Simplified Diagram
7V TO 28V
IN
EN
I.C.
Q1
DH
MAX16821
Q2
DL
OVI CSP
CLP PGND
C1
VLED
L1
C2
Q3
R1
Typical Operating Circuit and Selector Guide appear at end
of data sheet.
HIGH-FREQUENC.Y
PULSE TRAIN
NOTE: MAXIM PATENT-PENDING TOPOLOGY
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1 page  
High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
www.daEtasLhEeeCt4uT.cRomICAL CHARACTERISTICS (continued)
(VCC = 5V, VDD = VCC, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP
ENABLE INPUT (EN)
EN Input-Voltage High
EN rising
2.437 2.5
EN Input Hysteresis
0.28
EN Pullup Current
THERMAL SHUTDOWN
IEN
13.5 15
Thermal Shutdown
165
Thermal-Shutdown Hysteresis
20
Note 1: All devices are 100% production tested at +25°C. Limits over temperature are guaranteed by design.
Note 2: Does not include an error due to finite error amplifier gain. See the Voltage-Error Amplifier section.
MAX
2.562
16.5
UNITS
V
V
µA
°C
°C
Typical Operating Characteristics
(VIN = 12V, VDD = VCC = 5V, TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT (IQ) vs. FREQUENCY
10
9
EXTERNAL CLOCK
NO DRIVER LOAD
8
7 VIN = 24V
6
5
4
3 VIN = 5V
VIN = 12V
2
1
0
100 300 500 700 900 1100 1300 1500
FREQUENCY (kHz)
SUPPLY CURRENT vs. TEMPERATURE
70
65
60
55
50
45
40
-40
VIN = 12V
CDH/DL = 22nF
-15 10 35 60
TEMPERATURE (°C)
85
VCC LOAD REGULATION vs. VIN
5.5
5.4
5.3
5.2 VIN = 24V
5.1 VIN = 12V
5.0
4.9
4.8 VIN = 7V
4.7
4.6
4.5
0 15 30 45 60 75 90 105 120 135 150
VCC LOAD CURRENT (mA)
200
180
160
140
120
100
80
60
40
20
0
0
DRIVER RISE TIME
vs. DRIVER LOAD CAPACITANCE
DH
DL
5 10 15 20
LOAD CAPACITANCE (nF)
25
DRIVER FALL TIME
vs. DRIVER LOAD CAPACITANCE
100
80
60
40 DL
DH
20
0
0 5 10 15 20 25
LOAD CAPACITANCE (nF)
HIGH-SIDE DRIVER (DH) SINK
AND SOURCE CURRENT
MAX16821A toc06
CLOAD = 22nF
VIN = 12V
2A/div
100ns/div
_______________________________________________________________________________________ 5
5 Page 
High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
www.datasheet4u.com
Current-Error Amplifier
The MAX16821A/MAX16821B/MAX16821C include a
transconductance current-error amplifier with a typical
gm of 550µS and 320µA output sink and source capa-
bility. The current-error amplifier output (CLP) is con-
nected to the inverting input of the PWM comparator.
CLP is also externally accessible to provide frequency
compensation for the inner current regulation loop
(Figure 2). Compensate CEA so the inductor current
negative slope, which becomes the positive slope to
the inverting input of the PWM comparator, is less than
the slope of the internally generated voltage ramp (see
the Compensation section). In applications without syn-
chronous rectification, the LED driver can be turned off
and on instantaneously by shorting or opening the CLP
to ground.
PWM Comparator and R-S Flip-Flop
An internal PWM comparator sets the duty cycle by
comparing the output of the current-error amplifier to a
2VP-P ramp signal. At the start of each clock cycle, an
R-S flip-flop resets and the high-side driver (DH) turns
on if MODE is connected to SGND, and DL turns on if
MODE is connected to VCC. The comparator sets the
flip-flop as soon as the ramp signal exceeds the CLP
voltage, thus terminating the ON cycle. See Figure 3.
Differential Amplifier
The differential amplifier (DIFF) allows LED current sens-
ing (Figure 2). It provides true-differential LED current
sensing, and amplifies the sense voltage by a factor of 1
(MAX16821A), 6 (MAX16821B), and 20 (MAX16821C),
while rejecting common-mode voltage errors. The VEA
provides the difference between the differential amplifier
output (DIFF) and the desired LED current-sense volt-
age. The differential amplifier has a bandwidth of 1.7MHz
(MAX16821A), 1.6MHz (MAX16821B), and 550kHz
(MAX16821C). The difference between SENSE+ and
SENSE- is regulated to +0.6V (MAX16821A), +0.1V
(MAX16821B), or +0.03V (MAX16821C).
CLP
CSP
CSN
IN
RAMP
CLK
SHDN
60mV
PEAK-CURRENT
COMPARATOR
AV = 34.5
gm = 550µS
PWM
COMPARATOR
Figure 3. MAX16821A/MAX16821B/MAX16821C Phase Circuit
MODE = GND
SQ
RQ
BST
DH
LX
VDD
DL
PGND
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 25 Páginas | |
| PDF Descargar | [ Datasheet MAX16821A.PDF ] | |
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