Document Number: MC34845
Rev. 8.0, 5/2015
Freescale Semiconductor
Technical Data
© Freescale Semiconductor, Inc., 2011 - 2015. All rights reserved.
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
Figure 1. 34845 Simplified Application Diagram
34845
LED DRIVER
98ASA00602D
24-PIN QFN-EP
12V
FAIL
PGNDB
34845
SWA
SWB
VOUT
PGNDA
CH1
CH2
CH3
CH4
CH5
CH6
EP
EN
PWM
ISET
VIN
VDC1
VDC2
COMP
WAKE
~
~~
~~
~~
~~
~~
~
OVP
GND GND
CONTROL
UNIT
5V
Applications
• PC notebooks
• Netbooks
• GPS screens
• Portable DVD players
• Picture frames
• Smaller screen televisions
• Industrial/instrumentation displays
• Health care device displays
Analog Integrated Circuit Device Data
2Freescale Semiconductor
34845
1 Orderable Parts
Table 1. Device Variations
Part Number (1) Temperature
(TA)Package
Boost Switch Current Limit
IBOOST_LIMIT (A)
Switching Frequency
fS (kHz)
Slope Compensation VSLOPE
(V/s)
Min Typ Max Min Typ Max Min Typ Max
MC34845CEP -40 to 85 °C 24 QFN-EP 1.9 2.1 2.3 540 600 660 -0.52 -
MC34845DEP 2.1 2.35 2.6 270 300 330 0.22
Notes
1. To order parts in Tape and Reel, add the R2 suffix to the part number.
Analog Integrated Circuit Device Data
Freescale Semiconductor 3
34845
2 Internal Block Diagram
Figure 2. 34845 Simplified Internal Block Diagram
VIN
VDC1
COMP
EN
PWM
ISET
SWA
SWB
PGNDB
FAIL
CH1
CH2
CH3
CH4
CH5
CH6
6 CHANNEL
BOOST
LOGIC
CONTROLLER
CURRENT
MIRROR
V SENSE
GND
PGNDA
LDO
VDC2
VOUT
BANDGAP
CIRCUIT
WAKE LOW POWER
MODE
Analog Integrated Circuit Device Data
4Freescale Semiconductor
34845
3 Pin Connections
3.1 Pinout Diagram
Figure 3. 34845 Pin Connections
3.2 Pin Definitions
Table 2. 34845 Pin Definitions
Pin Number Pin Name Definition
1VIN 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.
2 PGNDB Power ground. This is the ground pin for the internal Boost FET.
3SWB Boost switch node connection B. Switching node of boost converter.
4SWA Boost switch node connection A. Switching node of boost converter.
5 PGNDA Power ground. This is the ground pin for the internal Boost FET.
6EN Enable pin (active high, internal pull-down).
7 - 12 CH1 - CH6 LED string connections 1 to 6. LED current drivers. Each line has the capability of driving up to 30 mA.
13, 19, 21 GND Ground Reference for all internal circuits other than the Boost FET. The Exposed Pad (EP) should be used for thermal
heat dissipation.
14 FAIL
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.
15 ISET LED current setting. The maximum current is set using a resistor from this pin to GND.
16 PWM External PWM control signal.
17 COMP 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.
18 WAKE 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.
20 VDC1 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 F should be connected between this pin and ground.
22 OVP External boost overvoltage setting. Requires a resistor divider from VOUT to GND. If no external OVP setting is desired,
this pin should be grounded.
VIN
PGNDB
SWB
SWA
PGNDA
GND
EN
WAKE
ISET
FAIL
VOUT
VDC2
OVP
COMP
VDC1
GND
GND
PWM
CH1
CH2
CH3
CH4
CH5
CH6
24
17
18
1920212223
1
87
6
5
4
3
2
16
9101112
13
14
15
EP GND
TRANSPARENT
TOP VIEW
Analog Integrated Circuit Device Data
Freescale Semiconductor 5
34845
23 VDC2 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 F should be connected between this pin and ground.
24 VOUT Boost voltage output feedback.
EP EP Ground and thermal enhancement pad
Table 2. 34845 Pin Definitions (continued)
Pin Number Pin Name Definition
Analog Integrated Circuit Device Data
6Freescale Semiconductor
34845
4 Electrical Characteristics
4.1 Absolute Maximum Ratings
Table 3. 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.
Symbol Ratings Value Unit Notes
ELECTRICAL RATINGS
VMAX
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
-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
V
ILED_MAX Maximum LED Current per Channel 33 mA
VESD
ESD Voltage
Human Body Model (HBM)
Machine Model (MM)
2000
200
V(2)
THERMAL RATINGS
TAOperating Ambient Temperature Range -40 to 85 °C
TJMaximum Junction Temperature 150 °C
TS Storage Temperature Range -40 to 150 °C
TPPRT Peak Package Reflow Temperature During Reflow Note 4 °C (3), (4)
TJA Thermal Resistance Junction to Ambient 36 °C/W (5)
TJC Thermal Resistance Junction to Case 3.1 °C/W (6)
PD
Power Dissipation
• TA = 25 °C
• TA = 85 °C
3.4
1.8
W(5)
Notes
2. ESD testing is performed in accordance with the Human Body Model (HBM) (AEC-Q100-2) (CZAP = 100 pF, RZAP = 1500 ), and the Machine
Model (MM) (CZAP = 200 pF, RZAP = 0
3. 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.
4. 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.
5. Per JEDEC51-8 Standard for Multilayer PCB.
6. Theoretical thermal resistance is from the die junction to the exposed pad.
Analog Integrated Circuit Device Data
Freescale Semiconductor 7
34845
4.2 Static and Dynamic Electrical Characteristics
Table 4. Static and Dynamic Electrical Characteristics
Characteristics noted under conditions VIN = 12 V, VOUT = 35 V, ILED = 30 mA, fS = 600 kHz, fPWM = 600 Hz - 40 C TA 85 C, unless
otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25 °C under nominal conditions, unless otherwise
noted.
Symbol Characteristic Min Typ Max Unit Notes
SUPPLY
VIN Supply Voltage 5.0 10 21 V
ISHUTDOWN
Supply Current when in Shutdown Mode
• EN = Low, PWM = Low -2.0 10 A
IOPERATIONAL
Supply Current when Operational Mode
• Boost = Pulse Skipping, Channels = 1% of Duty Cycle
EN = High, PWM = Low
-5.0 6.5 mA
UVLO Undervoltage Lockout
• VIN Rising 4.0 -4.4 V
UVLOHYST
Undervoltage Hysteresis
• VIN Falling -0.25 - V
VDC1
VDC1 Voltage
• CVDC1 = 2.2 F2.4 2.5 2.6 V(7)
VDC2
VDC2 Voltage (VIN between 7.0 V and 21 V)
• CVD2C = 2.2 F5.7 6.0 6.3 V(7)
BOOST
VOUT1
VOUT2
Output Voltage Range
• VIN = 5.0 V
• VIN = 21 V
8.0
24
-
-
43
60 V
(8)
IBOOST_LIMIT
Boost Switch Current Limit
• 34845C
• 34845D
1.9
2.1
2.1
2.35
2.3
2.6
A
tBOOST_TIME Boost Switch Current Limit Timeout -10 -ms
RDS(on)
RDSON of Internal FET
• IDRAIN= 1.0 A -300 520 mW
IBOOST_LEAK
Boost Switch Off State Leakage Current
• VSWA,SWB = 60 V - - 1.0 mA
VOUTLEAK
Feedback pin Off State Leakage Current
• VOUT = 60 V - - 500 mA
EFFBOOST
Peak Boost Efficiency
• VOUT = 33 V, RL = 330 -90 - % (9)
ILED/VIN
Line Regulation
• VIN = 7.0 V to 21 V, ICH = 30 mA -0.2 -0.2 %/V
ILED/VLED
Load Regulation
• VLED = 24 V to 40 V (all Channels), ICH = 30 mA -0.2 -0.2 %/V
DMIN Minimum Duty Cycle -10 15 %
DMAX Maximum Duty Cycle 88 90 - %
VOVP_INT
OVP Internally Fixed Value
• (no external voltage resistor divider) 56 60 64 V
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: fSW = 600 kHz, VIN = 12 V, VOUT = 33 V and RL = 330 . The following external
components are used: L = 10 H, DCR = 0.1 , COUT = 3x1 F (ceramic), Schottky diode VF = 0.35 V.
Analog Integrated Circuit Device Data
8Freescale Semiconductor
34845
BOOST (CONTINUED)
VOVP_EXT
OVP Programming Range
• (set through an external resistor divider) 15 -60 V(10)
VREF_OVP OVP Reference Voltage 6.3 6.9 7.5 V
ISINK_OVP OVP Sink Current -0.2 -A
fS
Switching Frequency
• 34845C
• 34845D
540
270
600
300
660
330
kHz
tSS Soft Start Time (fs = 600 kHz, 100% PWM duty) -3.0 -ms
SS_VOUT Soft Start VOUT Overshoot (fs = 600 kHz, 100% PWM duty) - - OVP V
BOOST_tRBoost Switch Rise Time -8.0 -ns
BOOST_tFBoost Switch Fall Time -6.0 -ns
ACSA Current sense Amplifier Gain -9.0 -
GMOTA Transconductance -200 -S
ISS Transconductance Sink and Source Current Capability -100 -A
VSLOPE
Slope Compensation
• 34845C
• 34845D
-
-
0.52
0.22
-
-
V/s
LED DRIVER
ILED
LED Driver Sink Current
• RISET = 51 k 0.1%, PWM = 3.3 V
• RISET = 5.1 k 0.1%, PWM = 3.3 V
2.88
29.4
3.0
30
3.12
30.6
mA
VISET
ISET Pin Voltage
• RISET = 5.1 k 0.1% 2.011 2.043 2.074 V
VMIN
Regulated Minimum Voltage Across LED Drivers
• Pulse Width > 400 ns 0.675 0.75 0.825 V
ITOLERANCE
LED Current Channel to Channel Tolerance
• 10 mA ILED 30 mA
• 3.0 mA ILED < 10 mA
-2.0
-4.0
-
-
2.0
4.0
%
ICH_LEAK
Off State leakage Current, All Channels
• VCH = 45 V - - 1.0 A
tR/tFLED Channels Rise and Fall Time -50 75 ns
OFDV LED Open Protection, Channel Disabled if VCH OFDV - - 0.55 V
SFDV
LED Short Protection Voltage, Channel Disabled if VCH SFDV
(channel on time 10s) 6.5 7.0 7.5 V
FAIL PIN
IFAIL_LEAK
Off State Leakage Current
• VFAIL = 5.5 V - - 5.0 A
VOL
On State Voltage Drop
• ISINK = 4.0 mA - - 0.4 V
OVERTEMPERATURE SHUTDOWN
OTTSHUTDOWN
Over-temperature Threshold (shutdown mode)
• Rising
• Hysteresis
150
-
165
25
-
-
°C
Notes
10. The OVP level must be set 5.0 V above the worst-case LED string voltage.
Table 4. Static and Dynamic Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 12 V, VOUT = 35 V, ILED = 30 mA, fS = 600 kHz, fPWM = 600 Hz - 40 C TA 85 C, unless
otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25 °C under nominal conditions, unless otherwise
noted.
Symbol Characteristic Min Typ Max Unit Notes
Analog Integrated Circuit Device Data
Freescale Semiconductor 9
34845
PWM INPUT
PWMCONTROL
PWM Dimming Mode LED Current Control
• PWM = 3.3 V, fPWM = 600 Hz 10% duty;
• PWM = 3.3 V, fPWM = 600 Hz 50% duty
• PWM = 3.3 V, fPWM = 600 Hz 100% duty
9.9
49.5
-
10
50
100
10.1
50.5
-
%
tPWM_IN
Input Minimum Pulse PWM Pin (VPWM = 3.3 V)
• Start-up (Wake mode)
• Operational (Wake mode)
• Start-up (Enable mode)
• operational (Enable mode)
1.6
-
0.4
-
-
0.2
-
0.2
-
-
-
-
s
fPWM Input Frequency Range for PWM Pin DC -100 kHz
WAKE
tSHUTDOWN Shutdown Mode Timeout 27 30 33 ms
LOGIC INPUTS (PWM)
VILL Input Low Voltage -0.3 -0.5 V
VIHL Input High Voltage 1.5 -5.5 V
ISINK Input Current -1.0 -1.0 A
LOGIC INPUTS (EN)
VILL Input Low Voltage -0.3 -0.5 V
VIHL Input High Voltage 2.1 -21 V
ISINK Input Current (VEN = 12 V) -6.0 10 A
LOGIC INPUTS (WAKE)
VILL Input Low Voltage -0.3 -0.5 V
VIHL Input High Voltage 2.1 -5.5 V
ISINK Input Current -1.0 -1.0 A
Table 4. Static and Dynamic Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 12 V, VOUT = 35 V, ILED = 30 mA, fS = 600 kHz, fPWM = 600 Hz - 40 C TA 85 C, unless
otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25 °C under nominal conditions, unless otherwise
noted.
Symbol Characteristic Min Typ Max Unit Notes
Analog Integrated Circuit Device Data
10 Freescale Semiconductor
34845
5 Functional Description
5.1 Introduction
LED backlighting has been popular for use in small LCD displays for many years. This technology is now rapidly replacing the incumbent
Cold Cathode Fluorescent Lamp (CCFL) in mid-size displays such as those used use in notebooks, monitors, and industrial/ consumer
displays. LEDs offer a number of advantages compared to the CCFL, including lower power, thinner, longer lifetime, low voltage drive,
accurate wide-range dimming control, and advanced architectures for improved image quality. LEDs are also void of hazardous materials
such as mercury which is used in CCFL.
LED backlights use different architecture depending on the size of the display and features required. For displays in the 10” to 17” + range
such as those used in notebooks, edge-lit backlights offer very thin designs down to 2.0 mm or less. The efficiency of the LED backlight
also extends battery life in portable equipment compared to CCFL. In large size panels, direct backlights support advanced architectures
such as local dimming, in which power consumption and contrast ratio are drastically improved. Edge lighting can also be used in large
displays when low cost is the driving factor.
The 34845 targets mid size panel applications in the 10” to 17” + range with edge-lit backlights. The device supports LED currents up to
30 mA and supports up to six strings of LEDs. This enables backlights up to 10 W to be driven from a single device. The device includes
a boost converter to deliver the required LED voltage from either a two or three cell Li-ion battery, or a direct 12 V input supply. The current
drivers match the current between devices to provide superior uniformity across the display. The 34845 provides for a wide range of PWM
dimming from a direct PWM control input.
5.2 Functional Device Operation
5.2.1 Power Supply
The 34845 supports 5.0 V to 21 V at the VIN input pin. Two internal regulators generate internal rails for internal operation. Both rails are
de-coupled using capacitors on the VDC1 and VDC2 pins. The VIN, VDC1, and VDC2 supplies each have their own UVLO mechanisms.
When any voltage is below the UVLO threshold, the device stops operating. All UVLO comparators have hysteresis to ensure constant
on/off cycling does not occur.
The power up sequence for applying VIN respect to the ENABLE and PWM signals is important since the 34845 device behaves differently
depending on how the sequence of these signals is applied. For the case where VIN is applied before the ENABLE and PWM signals, the
device has no limitation in terms of how fast the VIN ramp should be. However for the case where the PWM and ENABLE signals are
applied before VIN, the ramp up time of VIN between 0 V and 5.0 V should be no longer than 2.0 ms. Figure 4 and Figure 5 illustrate the
two different power up conditions.
Figure 4. Power up sequence case 1, VIN applied before the ENABLE and
PWM signals. No limitation for VIN ramp up time.
VIN
EN
PWM
VOUT
Boost
Soft St ar t
Analog Integrated Circuit Device Data
Freescale Semiconductor 11
34845
Figure 5. Power up sequence case 2, VIN applied after the ENABLE and PWM signals.
VIN ramp up time between 0 V and 5.0 V should be not higher than 2.0 ms
5.2.2 Boost Converter
The boost converter uses a Dynamic Headroom Control (DHC) loop to automatically set the output voltage needed to drive the LED
strings. The DHC is designed to operate under specific pulse width conditions in the LED drivers. It operates for pulse widths higher than
400 ns. If the pulse widths are shorter than specified, the DHC circuit does not operate and the voltage across the LED drivers increase
to a value given by the OVP, minus the total LED voltage in the LED string. It is therefore imperative to select the proper OVP level to
avoid exceeding the max off state voltage of the LED drivers (45 V).
The boost operates in current mode and is compensated externally through a type 2 network on the COMP pin. A modification of the
compensation network is suggested to minimize the amplitude of the ripple at VOUT. The details of the suggested compensation network
are shown in Figure 10 and Figure 11.
An integrated 2.0 A minimum FET supplies the required output current. An overcurrent protection circuit limits the output current cycle-
by-cycle to IOCP. If the condition exists longer than 10 ms, then the device shuts down. The frequency of the boost converter is internally
set to 300 kHz or 600 kHz, depending on the device’s version.
The boost also includes a soft start circuit. Each time the IC comes out of shutdown mode, the soft start period lasts for tSS.
Overvoltage protection is also included. The device has an internally fixed OVP value of 60 V (typical) which serves as a secondary fault
protection mechanism, in the event the externally programmed OVP fails (i.e. resistor divider opens up). While the internal 60 V OVP
detector can be used exclusively without the external OVP network, this is only recommended for applications where the LED string
voltage approaches 55 V or more. The OVP level can be set by using an external resistor divider connected between the output voltage
and ground with its output connected to the OVP pin. The OVP can be set up to 60 V by varying the resistor divider to match the OVP
internal reference of 6.9 V (typical).
5.2.3 LED Driver
The six channel LED driver provides current matching for six LED strings to within 2% maximum. The current in the strings is set using
a resistor tied to GND from the ISET pin. The LED current level is given by the equation: RSET = 153/ ILED. The accuracy of the RSET
resistor should be 0.1% for best performance.
5.2.4 LED Error Detect
If an LED is open, the output voltage ramps to the OVP level. If there is still no current in the LED string, the LED channel is turned off
and the output voltage ramps back down to normal operating level.
If LEDs are shorted and the voltage in any of the channels is greater than the SFDV threshold (7.0 V typical), then the device turns off this
channel. However if the on-time of the channels is less than 10 s, the SFDV circuit does not disable any of the channels, regardless of
the voltage across them. All the LED errors can be cleared by recycling the EN pin or applying a complete power-on-reset (POR).
VIN
EN
PWM
VOUT
Boost
Soft Start
5V
2ms
VIN ramp
UVLO Rising
Analog Integrated Circuit Device Data
12 Freescale Semiconductor
34845
5.2.5 WAKE Operation
The WAKE pin provides the means to set the device for low power consumption (shutdown mode) without the need of an extra logic signal
for enable. This is achieved by connecting the WAKE and PWM pins together, and tying the EN pin to ground. In this configuration, the
PWM signal is used to control the LED channels, while allowing low power consumption by setting the device into its shutdown mode every
time the PWM signal is kept low for longer time than the WAKE time out of 27 ms.
5.2.6 Overtemperature Shutdown and Temperature Control Circuits
The 34845 includes over-temperature protection. If the internal temperature exceeds the over-temp threshold OTTSHUTDOWN, then the
device shuts down all functions. Once the temperature falls below the low level threshold, the device is re-enabled.
5.2.7 FAIL Pin
The FAIL pin is at its low-impedance state when no error is detected. However, if an error such as an LED channel open or boost
overcurrent is detected, the FAIL pin goes into high-impedance. Once a failure is detected, the FAIL pin can be cleared by recycling the
EN pin or applying a complete power-on-reset (POR). If the detected failure is an Over-current time-out, the EN pin or a POR must be
cycled/executed to restart the part.
5.3 Typical Performance Curves
Figure 6. Typical System Efficiency vs Duty Cycle (FPWM = 25 kHz)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
0 102030405060708090100
Duty Cycle (%)
Efficiency (%)
Vin=9V
Fs = 600kHz
L=10uH, 68mOhm (IHLP2525CZE R100M01)
Schottky 5A, 100V (PDS5100HDICT-ND)
COUT = 2x2.2µF
FPWM=25kHz
Load = 9 LEDs, 20mA/channel
VLED = 27.8V, ±0.5V /channel
Analog Integrated Circuit Device Data
Freescale Semiconductor 13
34845
Figure 7. Typical ILED Dimming Linearity (FPWM = 25 kHz)
Figure 8. Typical Operating Waveforms (FPWM = 25 kHz, 50% duty)
Chablis ILED Dimming Linearity (FPWM=25kHz)
-2.000%
-1.500%
-1.000%
-0.500%
0.000%
0.500%
1.000%
1.500%
2.000%
110100
% Duty cycle
% ILED Channel mismatch
(-) Mismatch @ 25°C
(+) Mismatch @ 25°C
Chablis ILED Dimming Linearity (FPWM=25kHz)
-2.000%
-1.500%
-1.000%
-0.500%
0.000%
0.500%
1.000%
1.500%
2.000%
110100
% Duty cycle
% ILED Channel mismatch
(-) Mismatch @ 25°C
(+) Mismatch @ 25°C
PWM
VOUT (ac coupled)
VCH1
ILED1
PWM
VOUT (ac coupled)
VCH1
ILED1
Analog Integrated Circuit Device Data
14 Freescale Semiconductor
34845
Figure 9. Low Duty Dimming Operation Waveforms (FPWM = 25 kHz, 1% duty)
PWM
VOUT (ac coupled)
VCH1
ILED1
PWM
VOUT (ac coupled)
VCH1
ILED1
Analog Integrated Circuit Device Data
Freescale Semiconductor 15
34845
6 Typical Applications
6.1 Application Diagram
Figure 10. Typical Application Circuit for Single Wire Control, fS = 600 KHz
(VIN = 9.0 V, ILED/channel = 20 mA/channel, 10 LEDs/channel, OVP = 35 V, VPWM = 3.3 V)
MC 3484 5
CH5
CH1
CH2
CH3
33 uH
CH4
20
23
18
11
10
9
8
7
3
4
60 V, 1A LE D
LE G 2
VI N
LE D
LE G 1
CH6
12
LE D
LE G 3
SW A
SW B
LE D
LE G 4
LE D
LE G 5
LE D
LE G 6
4.7 uF
OVP
14 FAIL
22
1
VIN
2.2uF
10 V
VD C 1
2. 2uF
10 V
VD C 2
EN 6
24 VO U T
PG N D
2
5PG N D
WAKE
EP
10uf
25V
15
0.1 %
2113
GNDGND
PWM 16
680KΩ
167KΩ
4.7 uF
100 pF
100pF
100 pF
100 pF
100 pF
100p F
0. 1uf
220pF
COM P 17
33nF
kO10KΩ
Cont rol
Un it
3.3kΩ
/C
765KΩ
Caps should be located
as close as possible to the
MC34845 Device
7.65k
Analog Integrated Circuit Device Data
16 Freescale Semiconductor
34845
Figure 11. Typical Application Circuit for Single Wire Control, fS = 300 kHz
(VIN = 8.0V, ILED = 20 mA/channel, 14 LEDs/channel, OVP = 49V, VPWM = 3.3V)
6.2 Components Calculation
The following formulas are intended for the calculation of all external components related with the boost converter and network
compensation. To calculate the duty cycle, the internal losses of the MOSFET and diode should be taken into consideration:
The average input current depends directly on the output current when the internal switch is off.
6.2.1 Inductor
For calculating the Inductor, consider the losses of the internal switch and winding resistance of the inductor:
It is important to look for an inductor rated at least for the maximum input current:
MC 34845 B/D
CH5
CH1
CH2
CH3
33 u H
CH4
20
23
18
11
10
9
8
7
3
4
80 V, 1A LED
LEG 2
VIN
LED
LEG 1
CH6
12
LED
LEG 3
SWA
SWB
LED
LEG 4
LED
LEG 5
LED
LEG 6
OVP
14 FAIL
22
1
VI N
2.2uF
10V
VD C1
2.2uF
10 V
VD C2
EN 6
24 VOUT
PGND
2
5PGND
WAKE
EP
10 u f
25 V
15
0. 1 %
2113
GNDGND
PW M 16
100 pF
10 0 pF
10 0 pF
100 pF
10 0 pF
100 pF
0. 1 uf
220pF
COMP
56nF
2kΩ
Co nt ro l
Unit
2uF
10kΩ
114kΩ
680kΩ
2uF 2uF 2uF
765kΩ
Caps should be located
as close as possible to the
MC34845 Device
7.65k
D
VOUT VDVIN
–+
VOUT VDVSW
–+
-----------------------------------------------
=
IIN AVG–
IOUT
1D–
-------------
=
L
VIN VSW
–I
IN AVG–RINDUCTOR
–D
IIN AVG–rFSW
------------------------------------------------------------------------------------------------------------------
=
IIN MAX–IIN AVG–
VIN VOUT VIN
–
2LFSW
VOUT
---------------------------------------------------------
+=
Analog Integrated Circuit Device Data
Freescale Semiconductor 17
34845
6.2.2 Input Capacitor
The input capacitor should handle at least the following RMS current.
6.2.3 Output Capacitor
For the output capacitor selection the transconductance should be taken in consideration.
The output voltage ripple (∆VOUT) depends on the ESR of the Output capacitor. For a low output voltage ripple, it is recommended to use
ceramic capacitors which have a very low ESR. Since ceramic capacitor are costly, electrolytic or tantalum capacitors can be mixed with
ceramic capacitors for a less expensive solution.
The output capacitor should at least handle the following RMS current.
6.2.4 Network Compensation
Since this Boost converter is current controlled, a Type II compensation is needed. Note that before calculating the network compensation,
all boost converter components need to be known. For this type of compensation it is recommended to push out the Right Half Plane Zero
to higher frequencies where it does not significantly affect the overall loop.
The crossover frequency must be set much lower than the location of the Right half plane zero:
Since the system has a fixed slope compensation, RCOMP should be fixed for all configurations, i.e. RCOMP = 2.0 k
CCOMP1 and CCOMP2 should be calculated as follows:
The recommended values of these capacitors for an acceptable performance of the system in different operating conditions are
CCOMP1 = 33 nF and CCOMP2 = 220 pF.
A resistor network can be implemented from the PWM pin to ground with a connection to the compensation network, to improve the
transient response of the boost. This configuration should inject a 1.0 V signal to the COMP pin and the equivalent Thevenin resistance
of the divider should be close to RCOMP, (i.e. for 2.0 k COMP resistor, RCOMP = 3.3 k and RSHUNT = 10 k. See Figure 10 and
Figure 11 for implementation guidelines.
If a faster transient response is needed, a higher voltage (e.g. 1.3V) should be injected to the COMP pin; so the resistor divider should be
modified accordingly, but keeping the equivalent Thevenin resistance of the divider close to RCOMP.
IRMS CIN
–
VIN VOUT VIN
–
2LFSW
VOUT
---------------------------------------------------------
0.3=
COUT
RCOMP 5GM
IOUT
L
1D–VOUT
0.35
-------------------------------------------------------------------------------
=
ESRCOUT
VOUT VOUT
FSW
L
VOUT 1D–
---------------------------------------------------------------------------
=
IRMS COUT
–IOUT
D
1D–
-------------=
fRHPZ
VOUT 1D–
2
IOUT 2 L
---------------------------------------------
=
fCROSS
fRHPZ
5
---------------
=
CCOMP1
2
fCROSS
COMP
R
-------------------------------------------------------------
=
CCOMP2
2GM
6.28 FSW
-----------------------------
=
Analog Integrated Circuit Device Data
18 Freescale Semiconductor
34845
6.2.5 Variable definition
D = Duty cycle
VOUT = Output voltage
VD = Diode voltage
VIN = Input voltage
VSW = Internal switch voltage drop.
∆VOUT = Output voltage ripple
IIN-AVG = Average input current = IL-AVG
IOUT = Output current
IIN-MAX = Maximum input current
r = Current ripple ratio at the inductor = IL/ IL-AVG
IRMS-CIN= RMS current for the input capacitor
IRMS-COUT= RMS current for output capacitor
L = Inductor.
RINDUCTOR= Inductor winding resistor
FSW= Boost switching frequency
COUT = Output capacitor
RCOMP = Compensation resistor
GM= OTA transconductance
ESRCOUT= ESR of the output capacitor
fRHPZ= Right half plane zero frequency
fCROSS= Crossover frequency
CCOMP1= Compensation capacitor
CCOMP2= Shunt compensation capacitor
6.2.6 Component Suggestions
The Component Suggestions only apply to the conditions shown. Therefore, adjustments are necessary for different application
conditions.
Table 5. Component Suggestion Table
Application
Case VIN(min) VIN(Max) VO(max) VOVP fBOOST
ILED per
channel ROVP_UPPER ROVP_LOWER
19.0 V 12 V 30 V 35 V 600 kHz 20 mA 680 k167 k
26.0 V 12 V 43 V 48 V 300 kHz 23 mA 680 k114 k
Application
Case L(min)
L(min)
Continuous
mode
CIN(min) COUT(min) RCOMP at
VPWM =3.3V
RSHUNT at
VPWM =3.3 V
CCOMP1 CCOMP2
122 H33 H1x10 F; X7R;
25 V
2 x 4.7 F;
X7R; 50 V 3.3 k10 k33 nF 220 pF
222 H33 H1x10 F; X7R;
25 V
4 x 2.2 F;
X7R; 100 V 2.0 k16 k56 nF 220 pF
ISAT min = 2.6 A
Analog Integrated Circuit Device Data
Freescale Semiconductor 19
34845
7 Packaging
7.1 Package Mechanical Dimensions
Package dimensions are provided in package drawings. To find the most current package outline drawing, go to www.freescale.com and
perform a keyword search for the drawing’s document number.
Table 6. Packaging Information
Package Suffix Package Outline Drawing Number
24-Pin QFN-EP EP 98ASA00602D
Analog Integrated Circuit Device Data
20 Freescale Semiconductor
34845
Analog Integrated Circuit Device Data
Freescale Semiconductor 21
34845
Analog Integrated Circuit Device Data
22 Freescale Semiconductor
34845
8 Revision History
Revision Date Description of Changes
6.0 12/2011 • Changed the max rating for the OVP pin from 7.0V to 7.75V in the Absolute Maximum Ratings Table on page 6.
• Updated Freescale form and style.
7.0 6/2014 • No technical changes. Revised back page. Updated document properties. Added SMARTMOS sentence to first
paragraph.
8.0 5/2015
• Removed obsolete part numbers from Orderable Parts
• Updated Packaging
• Updated Freescale form and style
Document Number: MC34845
Rev. 8.0
5/2015
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There are no express or implied copyright licenses granted hereunder to design or fabricate any integrated circuits based
on the information in this document.
Freescale reserves the right to make changes without further notice to any products herein. Freescale makes no
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and all liability, including without limitation consequential or incidental damages. “Typical” parameters that may be
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may vary over time. All operating parameters, including “typicals,” must be validated for each customer application by
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respective owners.
© 2015 Freescale Semiconductor, Inc.
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