NXP Semiconductors
Data Sheet: Technical Data
Document Number: MC34845
Rev. 8.0, 8/2016
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 V 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;
34845C is 600 kHz, and the 34845D is 300 kHz. External compensation allows
the use of different inductor/ capacitor combinations.
The 34845 includes fault protection modes for LED short and open,
overtemperature, overcurrent and overvoltage 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 V to 21 V
• Boost output voltage up to 60 V
• 2.0 A integrated boost FET
• Fixed boost frequency - 300 kHz or 600 kHz
• OTP, OCP, UVLO fault detection
• LED short/open protection
• Programmable LED current between 3.0 mA and 30 mA
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
LED DRIVER
98ASA00602D
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
© 2016 NXP B.V.
1
Orderable parts
Table 1. Device variations
Part number
(1)
MC34845CEP
MC34845DEP
Temperature
(T
A
)
-40 to 85 °C
Package
Boost switch current limit
I
BOOST_LIMIT
(A)
Min.
24 QFN-EP
1.9
2.1
Typ.
2.1
2.35
Max.
2.3
2.6
Switching frequency
f
S
(kHz)
Min.
540
270
Typ.
600
300
Max.
660
330
Slope compensation V
SLOPE
(V/μs)
Min.
-
Typ.
0.52
0.22
Max.
-
Notes
1. To order parts in Tape and Reel, add the R2 suffix to the part number.
34845
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NXP Semiconductors
2
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
NXP Semiconductors
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3
3.1
Pin connections
Pinout diagram
VOUT
VDC2
VDC1
20
GND
GND
19
18 WAKE
17 COMP
16 PWM
EP GND
SWA
PGNDA
EN
4
5
6
7
CH1
8
CH2
9
CH3
10
CH4
11
CH5
12
CH6
15 ISET
14 FAIL
13 GND
OVP
22
TRANSPARENT
TOP VIEW
VIN
PGNDB
SWB
1
2
3
24
23
21
Figure 3. 34845 pin connections
3.2
Pin definitions
Table 2. 34845 Pin definitions
Pin number
1
2
3
4
5
6
7 - 12
13, 19, 21
Pin name
VIN
PGNDB
SWB
SWA
PGNDA
EN
CH1 - CH6
GND
Definition
Main voltage supply Input. IC Power input supply voltage, is used internally to produce internal voltage regulation for logic
functioning, and also as an input voltage for the boost regulator.
Power ground. This is the ground pin for the internal Boost FET.
Boost switch node connection B. Switching node of boost converter.
Boost switch node connection A. Switching node of boost converter.
Power ground. This is the ground pin for the internal Boost FET.
Enable pin (active high, internal pull-down).
LED string connections 1 to 6. LED current drivers. Each line has the capability of driving up to 30 mA.
Ground Reference for all internal circuits other than the Boost FET. The Exposed Pad (EP) should be used for thermal
heat dissipation.
Fault detected pin (open drain):
• No Failure = Low-impedance pull-down
• Failure = High-impedance
When a fault situation is detected, this pin goes into high-impedance.
LED current setting. The maximum current is set using a resistor from this pin to GND.
External PWM control signal.
Boost compensation component connection. This passive pin is used to compensate the boost converter. Add a
capacitor and a resistor in series to GND to stabilize the system as well as a shunt capacitor.
Low power consumption mode for single wire control. This is achieved by connecting the WAKE and PWM pins together
and grounding the ENABLE (EN) pin.
2.5 V internal voltage decoupling. This pin is for internal use only, and not to be used for other purposes. A capacitor of
2.2
μF
should be connected between this pin and ground.
External boost overvoltage setting. Requires a resistor divider from VOUT to GND. If no external OVP setting is desired,
this pin should be grounded.
14
FAIL
15
16
17
18
20
22
ISET
PWM
COMP
WAKE
VDC1
OVP
34845
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NXP Semiconductors
Table 2. 34845 Pin definitions (continued)
Pin number
23
24
EP
Pin name
VDC2
VOUT
EP
Definition
6.0 V internal voltage decoupling. This pin is for internal use only, and not to be used for other purposes. A capacitor of
2.2
μF
should be connected between this pin and ground.
Boost voltage output feedback.
Ground and thermal enhancement pad
34845
NXP Semiconductors
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