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Freescale Semiconductor Advance Information
Document Number: MC34845 Rev. 2.0, 9/2009
Low Cost 6 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 6 separate strings. The LED current tolerance in the 6 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 is 600 kHz, 34845A is 1.2 MHz and the 34845B 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. 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 4x4x0.65 mm 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
LED DRIVER
98ASA00087D 24-PIN QFN-EP
ORDERING INFORMATION
Device
MC34845EP/R2 MC34845AEP/R2 MC34845BEP/R2 Tape and Reel depicted with "R2" -40 to 85C 24 QFN-EP
Temperature Range (TA)
Package
Typical Applications * * * * * * * PC Notebooks Netbooks Picture Frames Portable DVD Players Small Screen Televisions Industrial Displays Medical Displays
5V
~
~
~
~
~
~
GND
Figure 1. 34845 Simplified Application Diagram
* This document contains certain information on a new product. Specifications and information herein are subject to change without notice.
(c) Freescale Semiconductor, Inc., 2009. All rights reserved.
DEVICE VARIATIONS
DEVICE VARIATIONS
Table 1. Device Variations
Characteristic Boost Switch Current Limit 34845, 34845A 34845B Switching Frequency 34845 34845A 34845B Slope Compensation 34845 34845A 34945B VSLOPE 0.52 0.73 0.22 fS 540 1080 270 600 1200 300 660 1320 330 V/s Symbol IBOOST_LIMIT 1.9 2.1 2.1 2.35 2.3 2.6 kHz Min Typ Max Unit A
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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
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Analog Integrated Circuit Device Data Freescale Semiconductor
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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
(1)
Symbol
Value
Unit
VMAX -0.3 to 65 -0.3 to 45 -0.3 to 20 -0.3 to 7.0 -0.3 to 2.7 -0.3 to 5.5 -0.3 to 24 ILED_MAX VESD 2000 200 33
V
mA V
Human Body Model (HBM) Machine Model (MM) THERMAL RATINGS Operating Ambient Temperature Range Maximum Junction Temperature Storage Temperature Range Peak Package Reflow Temperature During Thermal Resistance Junction to Ambient(4)
(5)
TA TJ TS Reflow(2), (3) TPPRT TJA TJC PD
-40 to 85 150 -40 to 150 Note 3 36 3.1
C C C C C/W C/W W
Thermal Resistance Junction to Case Power Dissipation(4)
TA = 25C TA = 85C
3.4 1.8
Notes 1. 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 . 2. 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. 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.
4. 5.
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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 VIN = 12 V, VOUT = 35 V, ILED = 30 mA, fS = 600 kHz, fPWM = 600 Hz - 40C TA 85C, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C 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 VIN Rising Under-voltage Hysteresis VIN Falling VDC1 Voltage(6) CVDC1 = 2.2 F VDC2 Voltage(6) (VIN between 7.0 and 21 V) CVD2C = 2.2 F BOOST Output Voltage Range(7) VIN = 5.0 V VIN = 21 V Boost Switch Current Limit 34845, 34845A 34845B Boost Switch Current Limit Timeout RDSON of Internal FET IDRAIN= 1.0 A Boost Switch Off state Leakage Current VSWA,SWB = 60 V Feedback pin Off-state Leakage Current VOUT = 60 V Peak Boost Efficiency(8) VOUT = 33 V, RL = 330 EFFBOOST 90 VOUTLEAK 500 % IBOOST_LEAK 1.0 A tBOOST_TIME RDSON 300 520 A VOUT1 VOUT2 IBOOST_LIMIT 1.9 2.1 2.1 2.35 10 2.3 2.6 ms m 8.0 24 43 60 A V VDC2 5.7 6.0 6.3 VDC1 2.4 2.5 2.6 V UVLOHYST 0.25 V UVLO 4.0 4.4 V 5.0 6.5 V IOPERATIONAL VIN ISHUTDOWN 2.0 10 mA 5.0 10 21 V A Symbol Min Typ Max Unit
Notes 6. This output is for internal use only and not to be used for other purposes 7. Minimum and maximum output voltages are dependent on Min/Max duty cycle condition. 8. 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.
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Analog Integrated Circuit Device Data Freescale Semiconductor
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ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 3. 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 - 40C TA 85C, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions, unless otherwise noted.
Characteristic BOOST (CONTINUED) Line Regulation VIN = 7.0 V to 21 V, ICH = 30 mA Load Regulation VLED = 24 V to 40 V (all Channels), ICH = 30 mA Minimum Duty Cycle Maximum Duty Cycle OVP Internally Fixed Value (no external voltage resistor divider) OVP Programming Range(9) (set through an external resistor divider) OVP Reference Voltage OVP Sink Current Switching Frequency 34845 34845A 34845B Soft Start Time (Fs=600 kHz, 100% PWM duty) Soft Start VOUT Overshoot (Fs=600 kHz, 100% PWM duty) Boost Switch Rise Time Boost Switch Fall Time Current sense Amplifier Gain OTA Transconductance Transconductance Sink and Source Current Capability Slope Compensation 34845 34845A 34945B LED DRIVER LED Driver Sink Current RISET = 51 k 0.1%, PWM = 3.3 V RISET = 5.1 k 0.1%, PWM = 3.3 V ISET Pin Voltage RISET = 5.1 k 0.1% Regulated Minimum Voltage Across LED Drivers Pulse Width > 400ns LED Current Channel to Channel Tolerance 10 mA ILED 30 mA 3.0 mA ILED < 10 mA Notes 9. The OVP level must be set 5.0 V above the worst-case LED string voltage. 34845 ITOLERANCE -2.0 -4.0 2.0 4.0 VMIN 0.675 0.75 0.825 % VISET 2.011 2.043 2.074 V ILED 2.88 29.4 3.0 30 3.12 30.6 V mA tSS SS_VOUT BOOST_tR BOOST_tF ACSA GM ISS VSLOPE 0.52 0.73 0.22 VREF_OVP ISINK_OVP fS 540 1080 270 600 1200 300 3.0 8.0 6.0 9.0 200 100 660 1320 330 OVP S A V/s ms V ns ns VOVP_EXT 15 6.3 6.9 0.2 60 7.5 V A kHz DMIN DMAX VOVP_INT 56 60 64 V ILED/VLED -0.2 88 10 90 0.2 15 % % V ILED/VIN -0.2 0.2 %/V %/V Symbol Min Typ Max Unit
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Analog Integrated Circuit Device Data Freescale Semiconductor
ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 3. 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 - 40C TA 85C, unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions, unless otherwise noted.
Characteristic LED DRIVER (CONTINUED) Off State leakage Current, All Channels VCH = 45 V LED Channels Rise and Fall Time LED Open Protection, Channel Disabled if VCH OFDV LED Short Protection Voltage, Channel Disabled if VCH SFDV (channel on time 10 s) FAIL PIN Off State Leakage Current VFAIL = 5.5 V On State Voltage Drop ISINK = 4.0 mA OVER-TEMPERATURE SHUTDOWN Over-temperature Threshold (shutdown mode) Rising Hysteresis PWM INPUT 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 Input Minimum Pulse PWM Pin (VPWM=3.3 V) Start-up (Wake Mode) Operational (Wake Mode) Start-up (Enable Mode) Operational (Enable Mode) Input Frequency Range for PWM Pin WAKE Shutdown Mode Timeout LOGIC INPUTS (PWM) Input Low Voltage Input High Voltage Input Current LOGIC INPUTS (EN) Input Low Voltage Input High Voltage Input Current (VEN = 12 V) LOGIC INPUTS (WAKE) Input Low Voltage Input High Voltage Input Current VILL VIHL ISINK -0.3 2.1 -1.0 0.5 5.5 1.0 V V A VILL VIHL ISINK -0.3 2.1 6.0 0.5 21 10 V V A VILL VIHL ISINK -0.3 1.5 -1.0 0.5 5.5 1.0 V V A tSHUTDOWN 27 30 33 ms fPWM tPWM_IN 1.6 0.4 DC 0.2 0.2 100 kHz PWMCONTROL 9.9 49.5 10 50 100 10.1 50.5 s % OTTSHUTDOWN 150 165 25 C VOL 0.4 IFAIL_LEAK 5.0 V A tR/tF OFDV SFDV 6.5 7.0 7.5 ICH_LEAK 50 1.0 75 0.55 ns V V A Symbol Min Typ Max Unit
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Analog Integrated Circuit Device Data Freescale Semiconductor
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PIN CONNECTIONS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
PIN CONNECTIONS
VOUT VDC2 VDC1 20 GND
TRANSPARENT TOP VIEW
VIN PGNDB SWB SWA PGNDA EN 1 2 3
24
23
22
21
19 18 WAKE 17 COMP 16 PWM
EP GND 4 5 6 7 CH1 8 CH2 9 CH3 10 CH4 11 CH5 12 CH6 15 ISET 14 FAIL 13 GND
Figure 3. 34845 Pin Connections Table 4. 34845 Pin Definitions
Pin Number 1 2 3 4 5 6 7 - 12 13, 19, 21 14 Pin Name VIN PGNDB SWB SWA PGNDA EN CH1 - CH6 GND FAIL 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 terminal 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 terminal 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. 15 16 17 18 20 22 ISET PWM COMP WAKE VDC1 OVP 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 terminal 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 F should be connected between this pin and ground. External boost over-voltage setting. Requires a resistor divider from VOUT to GND. If no external OVP setting is desired, this pin should be grounded.
34845
GND
OVP
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Analog Integrated Circuit Device Data Freescale Semiconductor
PIN CONNECTIONS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. 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 F should be connected between this pin and ground. Boost voltage output feedback. Ground and thermal enhancement pad
34845
Analog Integrated Circuit Device Data Freescale Semiconductor
9
FUNCTIONAL DESCRIPTION INTRODUCTION
FUNCTIONAL DESCRIPTION
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 7" to 17" range such as those used in notebooks, edge-lit backlights offer very thin designs down to 2mm 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 7" to 17" range with edge-lit backlights. The device supports LED currents up to 30mA and supports up to 6 strings of LEDs. This enables backlights up to 10W to be driven from a single device. The device includes a boost converter to deliver the required LED voltage from either a 2 or 3 cell Li-ion battery, or a direct 12V 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.
FUNCTIONAL DEVICE OPERATION
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 MC34845 device will behave 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 will have 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 0V and 5V should be no longer than 2ms. Figures 4 and 5 illustrate the two different power up conditions.
VIN EN PWM
Boost Soft Star t
VOUT
Figure 4. Power up sequence case 1, VIN applied before the ENABLE and PWM signals. No limitation for VIN ramp up time.
34845
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Analog Integrated Circuit Device Data Freescale Semiconductor
FUNCTIONAL DEVICE OPERATION INTRODUCTION
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).
EN PWM VIN
5V 2 ms
LED DRIVER
The 6 channel LED driver provides current matching for 6 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.
Boost Soft Start
VOUT
UVLO Rising VIN ramp
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 will turn off that channel. However if the on-time of the channels is less than 10 s, the SFDV circuit will 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).
Figure 5. Power up sequence case 2, VIN applied after the ENABLE and PWM signals. VIN ramp up time between 0V and 5V should be not higher than 2ms.
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 will not operate and the voltage across the LED drivers will 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 Figures 10 and 11. An integrated 2.0 A minimum FET supplies the required output current. An Over-current Protection circuit limits the output current cycle-by-cycle to IOCP. If the condition exists longer than 10 ms, then the device will shut down. The frequency of the boost converter is internally set to 300 kHz, 600 kHz or 1.2 MHz, 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. Over-voltage 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
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.
OVER-TEMPERATURE 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.
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 over-current 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 Overcurrent time-out, the EN pin or a POR must be cycled/ executed to restart the part.
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Analog Integrated Circuit Device Data Freescale Semiconductor
11
TYPICAL PERFORMANCE CURVES INTRODUCTION
TYPICAL PERFORMANCE CURVES
100.0 90.0 80.0 70.0 Efficiency (%) 60.0 50.0 40.0 30.0 20.0 10.0 0.0 0 10 20 30 40 50 60 70 80 90 100 Duty Cycle (%) Vin=9V Fs = 600kHz L=10uH, 68mOhm (IHLP2525CZER100M01) Schottky 5A, 100V (PDS5100HDICT-ND) COUT = 2x2.2F FPWM=25kHz Load = 9 LEDs, 20mA/channel VLED = 27.8V, 0.5V /channel
Figure 6. Typical System Efficiency vs Duty Cycle (FPWM=25kHz)
Chablis ILED Dimming Linearity (FPWM=25kHz)
2.000% 1.500%
(-) Mismatch @ 25C (+) Mismatch @ 25C
% ILED Channel mismatch
1.000% 0.500% 0.000% -0.500% -1.000% -1.500% -2.000% 1 10
100
% Duty cycle
Figure 7. Typical ILED Dimming Linearity (FPWM=25kHz)
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Analog Integrated Circuit Device Data Freescale Semiconductor
TYPICAL PERFORMANCE CURVES INTRODUCTION
PWM
VOUT (ac coupled)
VCH1
ILED1
Figure 8. Typical Operating Waveforms (FPWM=25kHz, 50% duty)
PWM
VOUT (ac coupled)
VCH1 ILED1
Figure 9. Low Duty Dimming Operation Waveforms (FPWM=25 kHz, 1% duty)
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Analog Integrated Circuit Device Data Freescale Semiconductor
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TYPICAL APPLICATIONS INTRODUCTION
TYPICAL APPLICATIONS
VIN
10 uH
60 V, 1A
LED LEG 1 2 .2uF 2.2 uF
LED LEG 2
LED LEG 3
LED LEG 4
LED LEG 5
LED LEG 6
10uf 25V
100 pF
100pF
100 pF
VIN 0. 1uf VD C1 VD C2 2 .2uF 10 V 2. 2uF 10 V
1
4 3
SWA SWB VOU T PGN D PGN D
Cap s should be l ocated as c lose as poss ible to the MC 34845 de vice
100 pF
20 23
24 2 5
100 pF
k 5.6 M O
100p F
22
OVP
k 1 MO
2 .2nF COM P
17
MC34845
7 8 9 10
CH1 CH2 CH3 CH4 CH 5 CH6
22 k kO
1 0 kO k
56 pF
EN Cont rol Un it PWM WAKE
11 6 16 18 15 14 13 GND EP 21 GND 12
F AIL
k 7.6 5 KO 0.1 %
Figure 10. Typical Application Circuit for Single Wire Control, fS = 600 KHz (VIN = 9.0 V, ILED/channel = 20 mA/channel, 12 LEDs/channel, OVP = 45 V, VPWM = 3.3 V)
VIN 4 .7uH
60 V, 1A
LED LEG 1 2 .2uF 2.2 uF
LED LEG 2
LED LEG 3
LED LEG 4
LED LEG 5
LED LEG 6
10uf 25V
100 pF
100pF
100 pF
VIN 0. 1uf VD C1 VD C2 2 .2uF 10 V 2. 2uF 10 V
1
4 3
SWA SWB VOU T PGN D PGN D
Cap s should be l ocated as c lose as poss ible to the MC 34845 de vice
100 pF
20 23
24 2 5
100 pF
k 5.6 M O
100p F
22
OVP
k 1 MO
2 .2nF COM P
17
MC34845A
7 8 9 10
CH1 CH2 CH3 CH4 CH 5 CH6
22 k kO
1 0 k kO
56 pF
EN Cont rol Un it PWM WAKE
11 6 16 18 15 14 13 GND EP 21 GND 12
F AIL
7.6 5 KO k 0.1 %
Figure 11. Typical Application Circuit for Single Wire Control, fS = 1.2 MHz (VIN = 9.0 V, ILED = 20 mA/channel, 12 LEDs/channel, OVP = 45 V, VPWM = 3.3 V)
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Analog Integrated Circuit Device Data Freescale Semiconductor
TYPICAL APPLICATIONS INTRODUCTION
VIN
33uH
80V, 1A 2.2uF 10uf 25V 100 pF 2. 2uF 2.2uF
LED LEG 1
LED LEG 2
LED LEG 3
LED LEG 4
LED LEG 5
LED LEG 6
100pF
100pF
VI N 0. 1uf VDC1 VDC2 2. 2uF 10V 2.2uF 10V
1
4 3
S WA S WB V OUT P GND P GND OVP
Caps should be located as cl ose as possi ble to the MC 34845 device
100 pF
20 23
24 2 5 22
100pF
1 MO
100 pF
162 kO 8.2nF COMP
17
MC34845 B
7 8 9 10
CH1 CH2 CH3 CH4 CH5 CH6
3.3 kO
150pF
EN Cont rol Unit PWM WAKE
11 6 16 18 15 14 13 GND EP 21 GND 12
FAIL
7. 65 K O 0. 1%
Figure 12. Typical Application Circuit for Single Wire Control, fS = 300 kHz (VIN = 8.0 V, ILED = 20 mA/channel, 14 LEDs/channel, OVP = 49 V, VPWM = 3.3 V)
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Analog Integrated Circuit Device Data Freescale Semiconductor
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TYPICAL APPLICATIONS COMPONENTS CALCULATION
COMPONENTS CALCULATION
The following formulas are intended for the calculation of all external components related with the boost converter and network compensation. In order to calculate the Duty Cycle, the internal losses of the MOSFET and Diode should be taken into consideration: V OUT + V D - V IN D = ---------------------------------------------V OUT + V D - V SW The average input current depends directly on the output current when the internal switch is off. I OUT I IN - AVG = -----------1-D Inductor For calculating the Inductor, consider the losses of the internal switch and winding resistance of the inductor: ( V IN - V SW - ( I IN - AVG x R INDUCTOR ) ) x D L = ----------------------------------------------------------------------------------------------------------------I IN - AVG x r x F SW It is important to look for an inductor rated at least for the maximum input current:
V IN x ( V OUT - V IN ) I IN - MAX = I IN - AVG + -------------------------------------------------------2 x L x F SW x V OUT 2 V OUT x ( 1 - D ) f RHPZ = -------------------------------------------I OUT x 2 x L
I RMS - C
OUT
D= I OUT x -----------1-D
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 will not significantly affect the overall loop.
Input Capacitor The input capacitor should handle at least the following RMS current.
I RMS - C V IN x ( V OUT - V IN ) = -------------------------------------------------------- x 0.3 2 x L x F SW x V OUT IN
The crossover frequency must be set much lower than the location of the Right half plane zero: f RHPZ f CROSS = -------------5 Since our system has a fixed slope compensation, RCOMP should be fixed for all configurations, i.e. RCOMP = 8.2 Kohm CCOMP1 and CCOMP2 should be calculated as follows:
2 C COMP1 = ---------------------------------------------------------------R 2 x f CROSS x COMP GM C COMP2 = ----------------------------6.28 x F SW
Output Capacitor For the output capacitor selection the transconductance should be taken in consideration.
R COMP x 5 x G M x I OUT x L C OUT = ------------------------------------------------------------------------------( 1 - D ) x V OUT x 0.35
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 that 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.
ESR C
OUT
V OUT x V OUT x F SW x L = -------------------------------------------------------------------------V OUT x ( 1 - D )
The output capacitor should at least handle the following RMS current. Network Compensation Since this Boost converter is current controlled, a Type II compensation is needed.
The recommended values of these capacitors for an acceptable performance of the system in different operating conditions are Ccomp1=2.2nF and Ccomp2=56pF. In order to improve the transient response of the boost a resistor divider has been implemented from the PWM pin to ground with a connection to the compensation network. This configuration should inject a 1V signal to the COMP pin and the equivalent Thevenin resistance of the divider is close to RCOMP, i.e. 10k and 39k. 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.
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Analog Integrated Circuit Device Data Freescale Semiconductor
TYPICAL APPLICATIONS COMPONENTS CALCULATION
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
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Analog Integrated Circuit Device Data Freescale Semiconductor
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PACKAGING PACKAGE DIMENSIONS
PACKAGING
PACKAGE DIMENSIONS
For the most current package revision, visit www.freescale.com and perform a keyword search using the "98A" listed below.
EP SUFFIX 24-PIN 98ASA00087D REVISION A 34845
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Analog Integrated Circuit Device Data Freescale Semiconductor
PACKAGING PACKAGE DIMENSIONS
EP SUFFIX 24-PIN 98ASA00087D REVISION A
34845
Analog Integrated Circuit Device Data Freescale Semiconductor
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PACKAGING
EP SUFFIX 24-PIN 98ASA00087D REVISION A
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Analog Integrated Circuit Device Data Freescale Semiconductor
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MC34845 Rev. 2.0 9/2009

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