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Document Number: MC34844

Rev. 9.0, 3/2012

Freescale Semiconductor

Advance Information

* This document contains certain information on a new product.

Specifications and information herein are subject to change without notice.

10 Channel LED Backlight Driver

with Integrated Power Supply

The 34844/A is a 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/A 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

C/SM Bus interface.

The 34844/A 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

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-clocks at a default

frequency of 600

kHz, but may be programmed via I

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 34844A has a default boost frequency of 320 kHz, but may be

programmed via I

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/A also supports optical/temperature closed loop

operation and also features LED over-temperature protection, LED

short protection, and LED open circuit protection. The IC also includes

over-voltage protection, over-current protection, and under-voltage

lockout.

Features

• Input voltage of 7.0 to 28 V

•2.5 A integrated boost FET

•Up to 50 mA on the 34844 LED current per channel

•Up to 80 mA on the 34844A LED current per channel

• 90% efficiency (DC:DC)

•I

C/SM Bus interface

• 10 channel current mirror with ±2% current matching

• Boost output voltage up to 60V, with Dynamic Headroom Control (DHC)

• PWM frequency programmable or synchronizable from 100 to 25,000 Hz for the 34844

• PWM frequency programmable or synchronizable from 110 to 27,000 Hz for the 34844A

• 32-Ld 5x5x1.0mm TQFN Package

Applications

• Monitors and HDTV - up to 42 inch

• Personal Computer Notebooks

• GPS Screens

• Small screen Televisions

LED DRIVER

34844

34844A

EP SUFFIX (PB-FREE)

98ASA10800D

32-PIN QFN-EP

ORDERING INFORMATION

Device

Temperature

Range (T

)

Package

MC34844EP/R2

-40 °C to 105 °C 32 QFN-EP

MC34844AEP/R2

Summary of content (62 pages)

PAGE 1
Freescale Semiconductor Advance Information Document Number: MC34844 Rev. 9.0, 3/2012 10 Channel LED Backlight Driver with Integrated Power Supply The 34844/A is a 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/A 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 I2C/SM Bus interface.
PAGE 2
34844 VIN VDC1 VDC2 7.0 to 28 V SWA SWB VOUT VDC3 PGNDA COMP PGNDB SLOPE Control Unit VDC1 VDC1 FAIL SCK SDA A0/SEN CK ISET PIN NIN ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ I0 I1 I2 I3 I4 I5 I6 I7 I8 I9 PWM M/~S EN VDC1 VCC GND Figure 1. MC34844 Simplified Application Diagram (SM Bus Mode) 34844A VIN 7.
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DEVICE VARIATIONS DEVICE VARIATIONS MC34844 is within the MC34844 Specifications Pages 4 to 31, MC34844A is within the MC34844A Specifications Pages 32 to 54 Table 1. Key Device Variations between the MC34844 and MC34844A Electrical Parameter(1) Condition Value Maximum LED Current mA 34844 55 34844A 85 LED Channel Sink Current (typ) 34844 RISET=5.1 kΩ ±0.1% 50 34844A RISET=3.48 kΩ ±0.1% 80 Switching Frequency 34844 34844A PWM Frequency Range 34844 Unit (typ) (BST [1:0]=0) 0.
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MC34844 MC34844 SPECIFICATIONS PAGES 4 TO 31 MC34844 SPECIFICATIONS PAGES 4 TO 31 34844 4 Analog Integrated Circuit Device Data Freescale Semiconductor
PAGE 5
MC34844 INTERNAL BLOCK DIAGRAM INTERNAL BLOCK DIAGRAM SWA VIN VDC1 VDC2 SWB LDO A0/SEN OVP VDC3 PGNDA COMP SLOPE BOOST CONTROLLER PGNDB VOUT CK EN CLOCK/PLL V SENSE FAIL M/~S PWM I0 PWM GENERATOR I1 I2 SCK SDA I2C INTERFACE 10 CHANNEL 50 mA CURRENT MIRROR I3 I4 I5 I6 I7 I8 ISET CURRENT DAC PIN TEMP/OPTO LOOP CONTROL NIN I9 OCP/OTP/UVLO GND Figure 3.
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MC34844 PIN CONNECTIONS VOUT VDC2 M/~S COMP VDC1 SCK SDA PWM PIN CONNECTIONS 32 31 30 29 28 27 26 25 VIN 1 24 CK PGNDB 2 23 VDC3 TRANSPARENT TOP VIEW SWB 3 SWA 4 22 SLOPE 21 NIN QFN - EP 5.0 MM X 5.0 MM 32 LEAD PGNDA 5 20 PIN EP GND A0/SEN 6 19 ISET EN 7 18 FAIL IO 8 EP = Exposed Pad 17 I9 9 10 11 12 13 14 15 16 I1 I2 I3 I4 I5 I6 I7 I8 Figure 4. 34844 Pin Connections Table 2.
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MC34844 PIN CONNECTIONS Table 2. 34844 Pin Definitions (continued) A functional description of each pin can be found in the Functional Pin Description section beginning on page 14.
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MC34844 ELECTRICAL CHARACTERISTICS MAXIMUM RATINGS ELECTRICAL CHARACTERISTICS MAXIMUM RATINGS Table 3. 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 Symbol Value Unit ELECTRICAL RATINGS Maximum Pin Voltages VMAX V A0/SEN 7.0 I0, I1, I2, I3, I4, I5, I6, I7, I8, I9,EN(5) 45 VIN 30 SWA, SWB, VOUT 65 FAIL, PIN, NIN, ISET, M/~S, CK, PWM 6.
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MC34844 ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 4. Static and Dynamic Electrical Characteristics Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, ILED = 50 mA, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1, - 40 °C ≤ TA ≤ 105 °C, PGND = 0 V, unless otherwise noted. Characteristic Symbol Min Typ Max Unit VIN 7.0 12 28 V Manual & SM Bus: EN = Low, SCK & SDA=Low - 2.
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MC34844 ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 4. Static and Dynamic Electrical Characteristics (continued) Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, ILED = 50 mA, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1, - 40 °C ≤ TA ≤ 105 °C, PGND = 0 V, unless otherwise noted. Characteristic Symbol Min Typ Max Unit IOUT/VIN -0.2 - 0.2 %/V IOUT/VLED -0.2 - 0.2 %/V VSLOPE - 0.49 - V/μs ACSA - 9.
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MC34844 ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 4. Static and Dynamic Electrical Characteristics (continued) Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, ILED = 50 mA, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1, - 40 °C ≤ TA ≤ 105 °C, PGND = 0 V, unless otherwise noted. Characteristic Symbol Min Typ Max Unit VNIN_DIS 2.2 - - V ININ -2.0 - 2.
PAGE 12
MC34844 ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 4. Static and Dynamic Electrical Characteristics (continued) Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, ILED = 50 mA, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1, - 40 °C ≤ TA ≤ 105 °C, PGND = 0 V, unless otherwise noted. Characteristic Symbol Min Typ Max Unit OVP = Fh OVPFH 60.5 62.5 64.5 V OVP = Eh OVPEH 56.5 58 60 V OVP = Dh OVPDH 53 54 56 V OVP = Ch OVPCH 49 51 52.
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MC34844 ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 4. Static and Dynamic Electrical Characteristics (continued) Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, ILED = 50 mA, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1, - 40 °C ≤ TA ≤ 105 °C, PGND = 0 V, unless otherwise noted.
PAGE 14
MC34844 FUNCTIONAL DESCRIPTION INTRODUCTION FUNCTIONAL DESCRIPTION INTRODUCTION LED backlighting has become very popular for small and medium LCDs, due to some advantages over other backlighting schemes, such as the widely used cold cathode fluorescent lamp (CCFL). The advantages of LED backlighting are low cost, long life, immunity to vibration, low operational voltage, and precise control over its intensity. However, there is an important drawback of this method.
PAGE 15
MC34844 FUNCTIONAL DESCRIPTION FUNCTIONAL PIN DESCRIPTION A0/SEN Address select, device select pin, or Hardware Overvoltage Protection (OVP) Control. CURRENT SET (ISET) Each LED string can drive up to 50 mA. The maximum current can be set by using a resistor from this pin to GND. POSITIVE CURRENT SCALING (PIN) Positive current scaling factor for the external analog current control. Applying 0 V to this pin, scales the current to near 0%, and in the same way, applying 2.
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MC34844 FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION MC34844 - Functional Block Diagram Regulators / Power Down Boost 3 Internal Regulators Protection / Failure Detection Over-temperature Protection Over-current Protection Under-voltage Protection Over-voltage Protection LED Open Protection LED Channels Logic Control Optical and Temperature Control PWM Dimming Serial Interface Control Regulator / Power down Protection / Failure Detection LED Channel
PAGE 17
MC34844 FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION Table 5.
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MC34844 FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION Also the device has a precharge voltage that add 0.5 Volts to the Boost, cycle by cycle of the PWM. It helps the boost to respond faster every time the load turns back on again. CURRENT MIRROR The programmable current mirror matches the current in 10 LED strings to within 2%. The maximum current is set using a resistor to GND from the ISET pin. This can be scaled down using the I2C interface to 255 levels.
PAGE 19
MC34844 FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION If I2C communication is not present, FAIL condition should be reset by removing the failure and re-enabling the device thru the EN pin. OPTICAL AND TEMPERATURE CONTROL LOOP The 34844 supports both optical and temperature loop control. Figure 6. Single Channel Disconnect Circuit. For applications where multiple failure detection is required, then one 100 kohm resistor must be placed from each channel to a diode (D2) connected to VDC2.
PAGE 20
MC34844 FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION shorted LED happens to be in the LED string with the highest forward voltage, the DHC circuit will automatically regulate the output voltage with respect to the new highest LED voltage. If more LEDs are shorted in the same LED string, it may cause excessive power dissipation in the channel which may cause the OTT circuit to trip which will completely shutdown the device.
PAGE 21
MC34844 FUNCTIONAL DEVICE OPERATION OPERATIONAL MODES FUNCTIONAL DEVICE OPERATION OPERATIONAL MODES NORMAL MODE I 2C In normal operation the 34844 is programed via to drive up to 50 mA of current through each one of the LED channels. The 34844 can be configured in master or slave mode as set by the M/~S pin. In Master mode, the internal PWM generator frequency is programmed through the I2C interface. The programmed value sets the number of 25 kHz clocks (40μs) in one PWM cycle.
PAGE 22
MC34844 FUNCTIONAL DEVICE OPERATION I2C BUS SPECIFICATION During manual mode, all internal Registers are in Default Configuration, refer Table 7, under this configuration the PIN and NIN pins are enabled to scale the current capability per string and may be disable by setting 2.2 V in the corresponding pin.
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MC34844 FUNCTIONAL DEVICE OPERATION LOGIC COMMANDS AND REGISTERS LOGIC COMMANDS AND REGISTERS Table 6.
PAGE 24
MC34844 FUNCTIONAL DEVICE OPERATION LOGIC COMMANDS AND REGISTERS Table 7. Register Description Register Name Default Value (Hex) BST[1:0] 2 ICH#[7:0] FF Channel Current Program (FFh = Maximum Current) ICHG[7:0] FF Global Current Program Description Boost Frequency (150,300,600,1200 kHz) [0h=150 Hz] Table 8.
PAGE 25
MC34844 FUNCTIONAL DEVICE OPERATION TYPICAL PERFORMANCE CURVES (TA=25°C) TYPICAL PERFORMANCE CURVES (TA=25°C) 95% 94% 93% Efficiency (%) 92% 91% 90% Fs = 600KHz L=22uH, DCR=52mO Schottky V12P10-E3/86A COUT = 2x4.7µF, 2x2.2µF/100V FPWM=600Hz, 100% duty Load = 16 LEDs, 50mA/channel VLED = 48V, ±1V /channel 89% 88% 87% 86% 85% 10 12 14 16 18 20 22 24 26 28 30 Vin, volts Figure 9. Boost efficiency vs Input Voltage 50.50 ILED (highest VLED channel), mA 50.
PAGE 26
MC34844 FUNCTIONAL DEVICE OPERATION TYPICAL PERFORMANCE CURVES (TA=25°C) 50.0 45.0 50.01 mA LED Current, mA 40.0 37.59 mA 35.0 30.0 25.0 25.03 mA 20.0 15.0 12.46 mA 10.0 FPWM=25KHz 5.0 0.0 0.4% 0.14 mA 25.0% 50.0% 75.0% 99.6% PWM Duty Cycle (%) Figure 11. PWM Dimming Linearity 10.10 10.08 10.06 Bias Current, mA 10.04 10.02 10.00 9.98 9.96 9.94 I2C Mode SM_Bus Mode Manual Mode 9.92 9.90 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Vin, volts Figure 12.
PAGE 27
MC34844 FUNCTIONAL DEVICE OPERATION TYPICAL PERFORMANCE CURVES (TA=25°C) 3.12 3.10 Bias Current, mA 3.08 3.06 3.04 3.02 I2C Mode 3.00 SM_Bus Mode 2.98 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Vin, volts Figure 13. Bias Current vs Input Voltage (Sleep Mode) COMP Vin=24V Load=16 LEDs, 50mA/channel VLED = 47V, ±1V VOUT INDUCTOR CURRENT Figure 14.
PAGE 28
MC34844 FUNCTIONAL DEVICE OPERATION TYPICAL PERFORMANCE CURVES (TA=25°C) ILED, CH1 ISET=40mA (all channels) FPWM=600Hz, 40% duty VCH1 VOUT (ac coupled) Precharge INDUCTOR CURRENT Figure 15. Typical Operation Waveforms for FPWM=600 Hz, 40% Duty SWA SWB INDUCTOR CURRENT VOUT (ac coupled) ILED, CH1 ISET=50mA (all channels) FPWM=600Hz, 100% duty Figure 16.
PAGE 29
MC34844 FUNCTIONAL DEVICE OPERATION TYPICAL PERFORMANCE CURVES (TA=25°C) VCh1 ISET = 20mA, FPWM=20KHz, Duty=0.78% (2LSB) ILED1 Figure 17. Low Duty Dimming Operation Waveforms (FPWM=20 kHz, 2LSB) VCh1 ISET = 20mA, FPWM=20KHz, Duty=0.39% (1LSB) ILED1 Figure 18.
PAGE 30
MC34844 TYPICAL APPLICATIONS TYPICAL APPLICATIONS MANUAL MODE (Single Wire Control) 22uH VIN = 24V 1 2 VOUT U1 1.0K 47uF 1 + 2.2uF 2.2uF 2.2uF 0 56pF 0 5.6K 309K 1.8nF 0 0 CLK VOUT 0 150K OVP = 55V 20K VDC1 5.1K VDC1 VDC1 VDC2 VDC3 29 22 COMP SLOPE 32 PGNDA PGNDB CK EN 25 PWM 27 26 SCK SDA 6 30 A0/SEN M/~S 19 ISET 20 21 PIN NIN 0 VOUT VIN 28 31 23 Master CK Output 24 7 SWA SWB 4 3 2 D1 1 LED MATRIX (16S10P) 13.
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MC34844 TYPICAL APPLICATIONS 22uH VIN = 24V 1 2 VOUT U3 1.0K 47uF 1 + 2.2uF 2.2uF 0 2.2uF 56pF 0 5.6K 309K 1.8nF Master CK 0 0 Control VDC1 0 SCK SDA Unit VDC1 5.1K VDC1 VIN 28 31 23 VDC1 VDC2 VDC3 29 22 COMP SLOPE 24 7 CK EN 25 PWM 27 26 SCK SDA 6 30 A0/SEN M/~S 19 ISET 20 21 PIN NIN 0 SWA SWB 4 3 VOUT 32 D8 2 1 LED MATRIX (16S10P) 13.8uF + 5 2 PGNDA PGNDB FAIL 18 I0 I1 I2 I3 I4 I5 I6 I7 I8 I9 8 9 10 11 12 13 14 15 16 17 GND 33 VCC 3.
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MC34844A MC34844A SPECIFICATIONS PAGES 32 TO 54 MC34844A SPECIFICATIONS PAGES 32 TO 54 34844A Analog Integrated Circuit Device Data Freescale Semiconductor 32
PAGE 33
MC34844A INTERNAL BLOCK DIAGRAM INTERNAL BLOCK DIAGRAM SWA VIN SWB VDC1 LDO VDC2 A0/SEN OVP VDC3 PGNDA COMP BOOST CONTROLLER SLOPE PGNDB VOUT CK CLOCK/PLL EN V SENSE FAIL M/~S PWM I0 PWM GENERATOR I1 I2 SCK SDA I2C INTERFACE 10 CHANNEL 80 mA CURRENT MIRROR I3 I4 I5 I6 I7 I8 ISET CURRENT DAC PIN TEMP/OPTO LOOP CONTROL NIN I9 OCP/OTP/UVLO GND Figure 23.
PAGE 34
MC34844A PIN CONNECTIONS VOUT VDC2 M/~S COMP VDC1 SCK SDA PWM PIN CONNECTIONS 32 31 30 29 28 27 26 25 VIN 1 24 CK PGNDB 2 23 VDC3 TRANSPARENT TOP VIEW SWB 3 SWA 4 22 SLOPE 21 NIN QFN - EP 5MM X 5MM 32 LEAD PGNDA 5 20 PIN EP GND A0/SEN 6 19 ISET EN 7 18 FAIL IO 8 EP = Exposed Pad 17 I9 9 10 11 12 13 14 15 16 I1 I2 I3 I4 I5 I6 I7 I8 Figure 24. 34844A Pin Connections Table 9.
PAGE 35
MC34844A PIN CONNECTIONS Table 9. 34844A Pin Definitions (continued) A functional description of each pin can be found in the Functional Pin Description section beginning on page 42.
PAGE 36
MC34844A ELECTRICAL CHARACTERISTICS MAXIMUM RATINGS ELECTRICAL CHARACTERISTICS MAXIMUM RATINGS Table 10. 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 Symbol Value Unit ELECTRICAL RATINGS Maximum Pin Voltages VMAX V A0/SEN 7.0 I0, I1, I2, I3, I4, I5, I6, I7, I8, I9(17) EN, VIN 45 30 SWA, SWB, VOUT 65 FAIL, PIN, NIN, ISET, M/~S, CK, PWM 6.
PAGE 37
MC34844A ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 11. Static and Dynamic Electrical Characteristics Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1, -40°C ≤ TA ≤ 105°C, PGND = 0 V, unless otherwise noted. Characteristic Symbol Min Typ Max Unit VIN 7.
PAGE 38
MC34844A ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 11. Static and Dynamic Electrical Characteristics (continued) Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1, -40°C ≤ TA ≤ 105°C, PGND = 0 V, unless otherwise noted. Characteristic Symbol Min Typ Max Unit IOUT/VIN -0.2 - 0.2 %/V IOUT/VLED -0.2 - 0.2 %/V VSLOPE - 0.49 - V/μs ACSA - 9.
PAGE 39
MC34844A ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 11. Static and Dynamic Electrical Characteristics (continued) Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1, -40°C ≤ TA ≤ 105°C, PGND = 0 V, unless otherwise noted. Characteristic Symbol Min Typ Max Unit VNIN_DIS 2.2 - - V ININ -2.0 - 2.
PAGE 40
MC34844A ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 11. Static and Dynamic Electrical Characteristics (continued) Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1, -40°C ≤ TA ≤ 105°C, PGND = 0 V, unless otherwise noted. Characteristic Symbol Min Typ Max Unit OVP = Fh (Default) OVPFH 60.5 62.5 64.5 V OVP = Eh OVPEH 56.5 58 60 V OVP = Dh OVPDH 53 54 56 V OVP = Ch OVPCH 49 51 52.
PAGE 41
MC34844A ELECTRICAL CHARACTERISTICS STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS Table 11. Static and Dynamic Electrical Characteristics (continued) Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1, -40°C ≤ TA ≤ 105°C, PGND = 0 V, unless otherwise noted. Characteristic Symbol Min Typ Max Unit fPWMS 110 - 27000 Hz 25000 27000 29000 Hz 103 110 112 tfPWM - 0.
PAGE 42
MC34844A FUNCTIONAL DESCRIPTION INTRODUCTION FUNCTIONAL DESCRIPTION INTRODUCTION LED backlighting has become very popular for small and medium LCDs, due to some advantages over other backlighting schemes, such as the widely used cold cathode fluorescent lamp (CCFL). The advantages of LED backlighting are low cost, long life, immunity to vibration, low operational voltage, and precise control over its intensity. However, there is an important drawback of this method.
PAGE 43
MC34844A FUNCTIONAL DESCRIPTION FUNCTIONAL PIN DESCRIPTION A0/SEN Address select, device select pin, or Hardware Overvoltage Protection (OVP) Control. CURRENT SET (ISET) Each LED string can drive up to 50 mA. The maximum current can be set by using a resistor from this pin to GND. POSITIVE CURRENT SCALING (PIN) Positive current scaling factor for the external analog current control. Applying 0 V to this pin, scales the current to near 0%, and in the same way, applying VSET (2.048 V Typ.
PAGE 44
MC34844A FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION MC34844 - Functional Block Diagram Regulators / Power Down Boost 3 Internal Regulators Protection / Failure Detection Over-temperature Protection Over-current Protection Under-voltage Protection Over-voltage Protection LED Open Protection LED Channels Logic Control Optical and Temperature Control PWM Dimming Serial Interface Control Regulator / Power down Protection / Failure Detection LED Channe
PAGE 45
MC34844A FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION Table 12.
PAGE 46
MC34844A FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION OVER-CURRENT PROTECTION (OCP) The boost converter also features internal Over-current Protection (OCP) and has a user programmable Overvoltage Protection (OVP). The OCP operates on a cycle by cycle basis. However, if the OCP condition remains for more than 10ms then the device turns off the LED Drivers, the Boost goes to Sleep mode and the output FAULT pin goes into high-impedance.
PAGE 47
MC34844A FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION DISABLING LED CHANNELS The 34844A allows the user to enable and disable each of the 10 channels separately by writing the corresponding CHENx bit on Registers 08 and 09 thru I2C. Since the enable and disable functions reconnects the feedback circuit of the LED drivers, this shouldn’t be used on any channel that shuts down either because an open LED channel condition or because is was previously POWER OFF.
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MC34844A FUNCTIONAL DEVICE OPERATION OPERATIONAL MODES FUNCTIONAL DEVICE OPERATION OPERATIONAL MODES NORMAL MODE In normal operation the 34844A is programed via I2C to drive up to 50 mA of current through each one of the LED channels. The 34844A can be configured in master or slave mode as set by the M/~S pin. In Master mode, the internal PWM generator frequency is programmed through the I2C interface. The programmed value sets the number of 27 kHz clocks (37μs) in one PWM cycle.
PAGE 49
MC34844A FUNCTIONAL DEVICE OPERATION I2C BUS SPECIFICATION charge of controlling LED dimming and enabling the device every time the PWM is active. For this configuration the EN pin should be LOW. I2C BUS SPECIFICATION The 34844A is a unidirectional device that can only be written by an external control unit. Since the device is a 7 bit address device (1110110), the control unit needs to follow a specific data transfer format which is shown in Table 26. Figure 26.
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MC34844A FUNCTIONAL DEVICE OPERATION LOGIC COMMANDS AND REGISTERS LOGIC COMMANDS AND REGISTERS Table 13.
PAGE 51
MC34844A FUNCTIONAL DEVICE OPERATION LOGIC COMMANDS AND REGISTERS Table 14. Register Description Register Name Default Value (Hex) FPWM[17:0] 300 PWM Frequency DPWM[7:0] FF PWM Duty Cycle (FFh =100%) CHEN[9:0] 3FF Channel Enable (0=off, 1=on) ALL_OFF 0 All 10 channels OFF at the same. In order to reactivate channels this bit should be clear. CLRFAIL 0 Clear fail if channels are re-enable.
PAGE 52
MC34844A TYPICAL APPLICATIONS TYPICAL APPLICATIONS MANUAL MODE (Single Wire Control) 22uH VIN = 24V 1 2 1.0K 47uF 1 + 2.2uF 2.2uF 0 2.2uF 56pF 0 5.6K 309K 1.8nF VDC1 VDC2 VDC3 29 22 COMP SLOPE Master CK Output 24 7 0 0 CLK VOUT VIN 28 31 23 0 150K OVP = 55V 20K VDC1 5.1K VDC1 PWM 27 26 SCK SDA 6 30 A0/SEN M/~S 19 ISET 20 21 PIN NIN 0 SWA SWB 4 3 VOUT 32 D1 2 1 13.
PAGE 53
MC34844A TYPICAL APPLICATIONS I2C MODE (Master Mode) 1 VIN = 24V 1 + 10uF 2.2uF 2.2uF 0 5.6K OUTPUT 0 MASTER CK VDC1 0 24 7 25 CONTROL UNIT VDC1 4.64K ISET = 60mA VDC1 SCK SDA 6 30 A0/SEN M/~S 19 ISET 20 21 PIN NIN 0 8 9 10 11 12 13 14 15 16 17 I0 I1 I2 I3 I4 I5 I6 I7 I8 I9 4.
PAGE 54
MC34844A TYPICAL APPLICATIONS LED MATRIX (40S8P) 1 150UH PDS3200 VIN = 60V to 72V 2 1 VDC2 1.0k 2.2uF EN_DLY 1 0 2.2uF 3.3nF 100pF 0 0 2.2uF 28 31 23 200k 0 EN_DLY 6.8K VOUT PWM = 200Hz (5V) 0 270K 4.
PAGE 55
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 a Duty Cycle, the internal losses of the MOSFET and Diode should be taken into consideration. Vout + V D – Vin D = --------------------------------------------Vout + V D – V SW The average input current depends directly to the output current when the internal switch is off.
PAGE 56
COMPONENTS CALCULATION 3 2 C Comp1 = -------------------------------------------------------f Cross × R Comp × π × 2 33 ×10 R SLOPE = ----------------------------V SLOPE × 5 GM C Comp2 = --------------------------6.28 × F SW In order to improve the transient response of the boost, on the 34844A, a resistor divider has been implemented from the PWM pin to ground with a connection to the compensation network. This configuration should inject a 1.
PAGE 57
LAYOUT GUIDELINES LAYOUT GUIDELINES RECOMMENDED STACK-UP SWITCHING NODE (SWA & SWB) The following table shows the recommended layer stackup for the signals to have good shielding and Thermal Dissipation. The components associated to this node must be placed as close as possible to each other to keep the switching loop small enough so that it does not contaminate other signals.
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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.
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PACKAGING PACKAGE DIMENSIONS EP SUFFIX 32-PIN 98ASA10800D REVISION O 34844 Analog Integrated Circuit Device Data Freescale Semiconductor 59
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PACKAGING PACKAGE DIMENSIONS EP SUFFIX 32-PIN 98ASA10800D REVISION O 34844 60 Analog Integrated Circuit Device Data Freescale Semiconductor
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REVISION HISTORY REVISION HISTORY REVISION DATE DESCRIPTION OF CHANGES 3.0 11/2008 • Initial Release 4.0 3/2009 • • • • 5.0 5/2009 • Corrected Compensation Components paragraph on page 32. 6.0 9/2009 • Added Part Number MC34844AEP/R2. 7.0 3/2010 8.0 7/2010 9.0 3/2012 • Combined Complete Data sheet for Part Numbers MC34844 and MC34844A to this data sheet. • Removed OVP=4h, OVP=3h and OVP=2h rows from Table 11. • PWM and CK Frequency range changed in Electrical Characteristics table.
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