Freescale Semiconductor
Technical Data
Document Number: MC34845
Rev. 7.0, 6/2014
Low Cost Six Channel LED
Backlight Driver with Integrated
Power Supply
The 34845 series represents high efficiency LED drivers for use in
backlighting LCD displays from 10” to 17”. Operating from supplies of
5.0 to 21 V, the 34845 series is capable of driving up to 16 LEDs in
series in six separate strings. The LED current tolerance in the six
strings is within ±2% maximum and is set using a resistor to GND.
PWM dimming is performed by applying a PWM input signal to the PWM
pin which modulates the LED channels directly. An Enable Pin (EN)
provides for low power standby. Alternatively, a single wire scheme
selects power down when PWM is connected to the Wake Pin and held
low.
The integrated boost converter uses dynamic headroom control to
automatically set the output voltage. There are three device versions for
boost frequency; 34845/C is 600 kHz, 34845A is 1.2 MHz and the
34845B/D is 300 kHz. External compensation allows the use of different
inductor/ capacitor combinations.
The 34845 includes fault protection modes for LED short and open, over
temperature, over current and over voltage errors. It features an
internally fixed OVP value of 60 V (typical) which protects the device in
the event of a failure in the externally programmed OVP. The OVP level
can be set by using an external resistor divider. This device is powered
using SMARTMOS technology.
Features
• Input voltage of 5.0 to 21 V
• Boost output voltage up to 60 V
• 2.0 A integrated boost FET
• Fixed boost frequency - 300 kHz, 600 kHz or 1.2 MHz
• OTP, OCP, UVLO fault detection
• LED short/open protection
• Programmable LED current between 3.0 mA and 30 mA
• 24-Ld 4x4x0.65mm
QFN
Package
34845
12V
VIN
VDC1
VDC2
VOUT
PGNDB
COMP
PGNDA
OVP
EN
CONTROL
UNIT
PWM
WAKE
ISET
FAIL
CH1
CH2
CH3
CH4
CH5
CH6
EP
GND
SWA
SWB
34845
34845A/B/C/D
LED DRIVER
98ASA00087D
24-PIN QFN-EP
Applications
• PC notebooks
• Netbooks
• GPS screens
• Portable DVD players
• Picture frames
• Smaller screen televisions
• Industrial/instrumentation displays
• Health care device displays
5V
~
~
~
~
~
~
GND
Figure 1. 34845 Simplified Application Diagram
© Freescale Semiconductor, Inc., 2011 - 2014. All rights reserved.
1
Orderable Parts
Table 1. Device Variations
Part Number
(1)
MC34845EP
MC34845AEP
MC34845BEP
MC34845CEP
MC34845DEP
-40 to 85 °C
24 QFN-EP
Temperature
Package
(T
A
)
Boost Switch Current Limit
I
BOOST_LIMIT
(A)
Min
1.9
1.9
2.1
1.9
2.1
Typ
2.1
2.1
2.35
2.1
2.35
Max
2.3
2.3
2.6
2.3
2.6
Switching Frequency
f
S
(kHz)
Min
540
1080
270
540
270
Typ
600
1200
300
600
300
Max
660
1320
330
660
330
Slope Compensation
V
SLOPE
(V/s)
Min
-
-
-
-
-
Typ
0.52
0.73
0.22
0.52
0.22
Max
-
-
-
-
-
Notes
1. To order parts in Tape and Reel, add the R2 suffix to the part number.
34845
2
Analog Integrated Circuit Device Data
Freescale Semiconductor
INTERNAL BLOCK DIAGRAM
INTERNAL BLOCK DIAGRAM
VIN
VDC1
VDC2
LDO
SWA
SWB
PGNDB
COMP
BOOST
CONTROLLER
PGNDA
VOUT
LOGIC
V SENSE
FAIL
EN
WAKE
LOW POWER
MODE
CH1
CH2
6 CHANNEL
CURRENT
MIRROR
CH3
CH4
CH5
CH6
PWM
BANDGAP
CIRCUIT
ISET
GND
Figure 2. 34845 Simplified Internal Block Diagram
34845
Analog Integrated Circuit Device Data
Freescale Semiconductor
3
ELECTRICAL CHARACTERISTICS
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
ABSOLUTE MAXIMUM RATINGS
Table 2. Absolute Maximum Ratings
All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or permanent
damage to the device.
Ratings
ELECTRICAL RATINGS
Maximum Pin Voltages
SWA, SWB, VOUT
CH1, CH2, CH3, CH4, CH5, CH6 (Off state)
CH1, CH2, CH3, CH4, CH5, CH6 (On state)
FAIL
OVP
COMP, ISET
PWM, WAKE
EN, VIN
Maximum LED Current per Channel
ESD Voltage
(2)
Human Body Model (HBM)
Machine Model (MM)
THERMAL RATINGS
Operating Ambient Temperature Range
Maximum Junction Temperature
Storage Temperature Range
Peak Package Reflow Temperature During Reflow
(3), (4)
Thermal Resistance Junction to Ambient
(5)
Thermal Resistance Junction to Case
(6)
Power Dissipation
(5)
T
A
= 25°C
T
A
= 85°C
T
A
T
J
T
S
T
PPRT
T
JA
T
JC
P
D
3.4
1.8
-40 to 85
150
-40 to 150
Note 4
36
3.1
°C
°C
°C
°C
°C/W
°C/W
W
I
LED_MAX
V
ESD
2000
200
V
MAX
-0.3 to 65
-0.3 to 45
-0.3 to 20
-0.3 to 7.0
-0.3 to 7.75
-0.3 to 2.7
-0.3 to 5.5
-0.3 to 24
33
mA
V
V
Symbol
Value
Unit
Notes
2. ESD testing is performed in accordance with the Human Body Model (HBM) (AEC-Q100-2) (C
ZAP
= 100 pF, R
ZAP
= 1500
),
and the
Machine Model (MM) (C
ZAP
= 200 pF, R
ZAP
= 0
3.
4.
Pin soldering temperature limit is for 10 seconds maximum duration. Not designed for immersion soldering. Exceeding these limits may
cause malfunction or permanent damage to the device.
Freescale’s Package Reflow capability meets Pb-free requirements for JEDEC standard J-STD-020C. For Peak Package Reflow
Temperature and Moisture Sensitivity Levels (MSL), Go to www.freescale.com, search by part number [e.g. remove prefixes/suffixes
and enter the core ID to view all orderable parts. (i.e. MC33xxxD enter 33xxx), and review parametrics.
Per JEDEC51-8 Standard for Multilayer PCB.
Theoretical thermal resistance is from the die junction to the exposed pad.
5.
6.
34845
4
Analog Integrated Circuit Device Data
Freescale Semiconductor
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 3. Static and Dynamic Electrical Characteristics
Characteristics noted under conditions V
IN
= 12 V, V
OUT
= 35 V, I
LED
= 30 mA, f
S
= 600 kHz, f
PWM
= 600 Hz - 40C
T
A
85C, unless otherwise noted. Typical values noted reflect the approximate parameter means at T
A
= 25°C under nominal
conditions, unless otherwise noted.
Characteristic
SUPPLY
Supply Voltage
Supply Current when in Shutdown Mode
EN = Low, PWM = Low
Supply Current when Operational Mode
Boost = Pulse Skipping, Channels = 1% of Duty Cycle
EN = High, PWM = Low
Under-voltage Lockout
V
IN
Rising
Under-voltage Hysteresis
V
IN
Falling
VDC1 Voltage
(7)
C
VDC1
= 2.2
F
VDC2 Voltage
(7)
Symbol
Min
Typ
Max
Unit
V
IN
I
SHUTDOWN
5.0
-
10
2.0
21
10
V
A
mA
I
OPERATIONAL
-
UVLO
4.0
UVLO
HYST
-
V
DC1
2.4
V
DC2
5.7
6.0
6.3
2.5
2.6
0.25
-
-
4.4
5.0
6.5
V
V
V
V
(V
IN
between 7.0 and 21 V)
C
VD2C
= 2.2
F
BOOST
Output Voltage Range
(8)
VIN = 5.0 V
VIN = 21 V
Boost Switch Current Limit
34845, 34845A, 34845C
34845B, 34845D
Boost Switch Current Limit Timeout
RDSON of Internal FET
I
DRAIN
= 1.0 A
Boost Switch Off state Leakage Current
V
SWA,SWB
= 60 V
Feedback pin Off-state Leakage Current
V
OUT
= 60 V
Peak Boost Efficiency
(9)
V
OUT
= 33 V, RL = 330
EFF
BOOST
VOUT
LEAK
I
BOOST_LEAK
t
BOOST_TIME
R
DSON
V
OUT1
V
OUT2
I
BOOST_LIMIT
8.0
24
1.9
2.1
-
-
-
-
-
-
-
2.1
2.35
10
300
-
-
90
43
60
V
A
2.3
2.6
-
520
A
1.0
A
500
%
-
ms
m
Notes
7. This output is for internal use only and not to be used for other purposes.
8. Minimum and maximum output voltages are dependent on Min/Max duty cycle condition.
9. Boost efficiency test is performed under the following conditions: f
SW
= 600 kHz, V
IN
= 12 V, V
OUT
= 33 V and R
L
= 330
.
The following
external components are used: L = 10
H DCR = 0.1
,
C
OUT
= 3x1
F (ceramic), Schottky diode V
F
= 0.35 V.
34845
Analog Integrated Circuit Device Data
Freescale Semiconductor
5
