Freescale Semiconductor
Technical Data
Document Number: MC34844
Rev. 10.0, 8/2014
10 Channel LED Backlight Driver
with Integrated Power Supply
The 34844 is a SMARTMOS high efficiency, LED driver for use in
backlighting LCD displays from 10" to 20"+. Operating from supplies of 7.0 to
28 V, the MC34844 is capable of driving up to 160 LEDs in 10 parallel strings.
Current in the 10 strings is matched to within
2%,
and can be programmed via
the I
2
C/SM Bus interface.
The 34844 also includes a Pulse Width Monitor (PWM) generator for LED
dimming. The LEDs can be dimmed to one of 256 levels, programmed through
the I
2
C/SM Bus interface. Up to 65,000:1 (256:1 PWM, 256:1 Current DAC)
dimming ratio.
The integrated boost converter generates the minimum output voltage
required to keep all LEDs illuminated with the selected current, providing the
highest efficiency possible.
The 34844 has an integrated boost self-clock at a default frequency of
600 kHz, but may be programmed via I
2
C to 150/300/600/1200 kHz. The PWM
frequency can be set from 100 Hz to 25 kHz, or can be synchronized to an
external input. If not synchronized to another source, the internal PWM rate
outputs on the CK pin. This enables multiple devices to be synchronized
together.
The 34844 has a default boost frequency of 320 kHz, but may be
programmed via I
2
C to 160/320/650/1300 kHz. The PWM frequency can be set
from 110 Hz to 27 kHz, or can be synchronized to an external input. If not
synchronized to another source, the internal PWM rate outputs on the CK pin.
This enables multiple devices to be synchronized together.
The 34844 also supports optical/temperature closed loop operation and
features LED overtemperature protection, LED short protection, and LED open
circuit protection. The IC includes overvoltage protection, overcurrent
protection, and undervoltage lockout.
Features
•
•
•
•
•
•
•
•
•
Input voltage of 7.0 to 28 V
2.5 A integrated boost FET
Up to 80 mA on the 34844 LED current per channel
90% efficiency (DC:DC)
I
2
C/SM Bus interface
10 channel current mirror with ±2.0% current matching
Boost output voltage up to 60V, with Dynamic Headroom Control (DHC)
PWM frequency programmable or synchronizable from 110 to 27,000 Hz
32-Ld 5x5x1.0 mm TQFN Package
34844
LED DRIVER
EP SUFFIX (PB-FREE)
98ASA10800D
32-PIN QFN-EP
Applications
•
•
•
•
Monitors and HDTV - up to 42 inch
Personal Computer Notebooks
GPS Screens
Small screen Televisions
© Freescale Semiconductor, Inc., 2009-2014. All rights reserved.
34844
7.0 to 28 V
VIN
VDC1
VDC2
VDC3
COMP
SLOPE
SCK
SDA
PWM
A0/SEN
CK
M/~S
EN
VDC1
ISET
PIN
NIN
GND
SWA
SWB
VOUT
PGNDA
PGNDB
FAIL
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
VCC
Control Unit
VDC1
~
~
~
~
~
~
~
~
~
~
VDC1
Figure 1. MC34844 Simplified Application Diagram (SM Bus Mode)
34844
7.0 to 28V
VIN
VDC1
VDC2
VDC3
SWA
SWB
VOUT
PGNDA
PGNDB
FAIL
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
VCC
VOUT
PWM
COMP
SLOPE
SCK
SDA
PWM
VDC1
A0/SEN
CK
M/~S
EN
VDC1
ISET
PIN
NIN
GND
~
~
~
~
~
~
~
~
~
~
Control Unit
PWM
VOUT
Figure 2. MC34844 Simplified Application Diagram (Manual Mode)
34844
2
Analog Integrated Circuit Device Data
Freescale Semiconductor
ORDERABLE PARTS
ORDERABLE PARTS
This section describes the part numbers available to be purchased along with their differences. Valid orderable part numbers are provided
on the web. To determine the orderable part numbers for this device, go to
http://www.freescale.com
and perform a part number search for
the following device numbers.
Table 1. Orderable Part Variations
Part Number
MC34844AEP
Notes
(1)
Temperature (T
A
)
-40 to 105 °C
32 QFN-EP
Package
Notes:
1. To order parts in Tape & Reel, add the R2 suffix to the part number.
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
3
INTERNAL BLOCK DIAGRAM
INTERNAL BLOCK DIAGRAM
VIN
VDC1
VDC2
VDC3
COMP
SLOPE
VOUT
CK
EN
M/~S
PWM
PWM GENERATOR
CLOCK/PLL
V SENSE
BOOST
CONTROLLER
LDO
OVP
SWA
SWB
A0/SEN
PGNDA
PGNDB
FAIL
I0
I1
I2
10 CHANNEL
80 mA CURRENT
MIRROR
I3
I4
I5
I6
I7
I8
SCK
SDA
I
2
C INTERFACE
ISET
CURRENT DAC
I9
PIN
NIN
TEMP/OPTO
LOOP CONTROL
OCP/OTP/UVLO
GND
Figure 3. 34844 Simplified Internal Block Diagram
34844
4
Analog Integrated Circuit Device Data
Freescale Semiconductor
PIN CONNECTIONS
PIN CONNECTIONS
COMP
VOUT
VDC2
VDC1
32
VIN 1
PGNDB 2
SWB 3
SWA 4
PGNDA 5
A0/SEN 6
EN 7
IO 8
31
30
29
28
27
26
PWM
25
24 CK
23 VDC3
22 SLOPE
21 NIN
20 PIN
19 ISET
18 FAIL
17 I9
16
I8
M/~S
SCK
14
I6
TRANSPARENT
TOP VIEW
QFN - EP
5MM X 5MM
32 LEAD
EP GND
EP = Exposed Pad
9
I1
10
I2
11
I3
12
I4
13
I5
Figure 4. 34844 Pin Connections
A functional description of each pin can be found in the Functional Pin Description section beginning on
page 13.
Table 2. 34844 Pin Definitions
Pin Number
1
2
3
4
5
6
7
8 - 17
18
19
20
21
22
23
24
25
Pin Name
VIN
PGNDB
SWB
SWA
PGNDA
A0/SEN
EN
I0-I9
FAIL
ISET
PIN
NIN
SLOPE
VDC3
CK
PWM
Pin Function
Power
Power
Input
Input
Power
Input
Input
Input
Open Drain
Passive
Input
Input
Passive
Output
Input/Output
Input
Formal Name
Input voltage
Power Ground
Switch node B
Switch node A
Power Ground
Device Select
Enable
LED Channel
Fault detection
Current set
Positive current scale
Input supply
Power ground
Boost switch connection B
Boost switch connection A
Power ground
Address select, device select pin or OVP HW control
Enable pin (active high, internal pull-up)
LED string connections
Fault detected pin (open drain):
No Failure = low-impedance
Failure = high-impedance
LED current setting resistor
Positive input analog current control
Definition
Negative current scale Negative input analog current control
Boost Slope
Internal Regulator 3
Clock signal
External PWM
Boost slope compensation setting resistor
Decoupling capacitor for internal phase locked loop power
Clock synchronization pin (input for M/~S = low - internal pull-up, output for
M/~S = high)
External PWM input (internal pull-down)
SDA
15
I7
Transparent Top View
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
5
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