34845A--Datasheet/数据表在线中文翻译

Document Number: MC34845

Rev. 2.0, 9/2009

Freescale Semiconductor

Advance Information

Low Cost 6 Channel LED

Backlight Driver with Integrated

Power Supply

34845

34845A/B

LED DRIVER

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.

98ASA00087D

24-PIN QFN-EP

ORDERING INFORMATION

Temperature

Package

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.

Device

Range (T )

A

MC34845EP/R2

MC34845AEP/R2

MC34845BEP/R2

-40° to 85°C

24 QFN-EP

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.

Tape and Reel depicted with “R2”

Typical Applications

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.

• PC Notebooks

• Netbooks

• Picture Frames

• Portable DVD Players

• Small Screen Televisions

• Industrial Displays

• Medical Displays

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 μQFN Package

34845

12V

VIN

SWA

SWB

VDC1

VDC2

VOUT

PGNDB

PGNDA

COMP

EN

OVP

5V

~

FAIL

PWM

CONTROL

UNIT

CH1

CH2

CH3

CH4

CH5

CH6

WAKE

ISET

GND EP 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.

DEVICE VARIATIONS

Table 1. Device Variations

Characteristic

Symbol

Min

Typ

Max

Unit

Boost Switch Current Limit

Switching Frequency

I_{BOOST_LIMIT}

34845, 34845A

A

1.9

2.1

2.3

2.6

34845B

2.35

f_S

kHz

34845

540

1080

270

600

1200

300

660

1320

330

34845A

34845B

Slope Compensation

V_SLOPE

V/μs

34845

-

0.52

0.73

0.22

-

34845A

34945B

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

2

INTERNAL BLOCK DIAGRAM

SWA

VIN

SWB

VDC1

VDC2

LDO

PGNDB

PGNDA

COMP

VOUT

BOOST

CONTROLLER

V SENSE

LOGIC

FAIL

EN

LOW POWER

MODE

WAKE

CH1

CH2

CH3

CH4

CH5

CH6

PWM

ISET

6 CHANNEL

CURRENT

MIRROR

BANDGAP

CIRCUIT

GND

Figure 2. 34845 Simplified Internal Block Diagram

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

3

ELECTRICAL CHARACTERISTICS

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

ABSOLUTE MAXIMUM RATINGS

Table 2. Absolute Maximum Ratings

All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or

permanent damage to the device.

Ratings

Symbol

Value

Unit

ELECTRICAL RATINGS

Maximum Pin Voltages

SWA, SWB, VOUT

V_MAX

V

-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

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

I_{LED_MAX}

V_ESD

33

mA

V

ESD Voltage⁽¹⁾

Human Body Model (HBM)

Machine Model (MM)

2000

200

THERMAL RATINGS

Operating Ambient Temperature Range

Maximum Junction Temperature

T

A

-40 to 85

150

°C

T_J

T_S

Storage Temperature Range

-40 to 150

Note 3

36

°C

Peak Package Reflow Temperature During Reflow^{(2), (3)}

Thermal Resistance Junction to Ambient⁽⁴⁾

Thermal Resistance Junction to Case⁽⁵⁾

T_PPRT

°C

T

°C/W

W

JA

θ

T

3.1

JC

θ

Power Dissipation⁽⁴⁾

TA = 25°C

P_D

3.4

1.8

TA = 85°C

Notes

1. ESD testing is performed in accordance with the Human Body Model (HBM) (AEC-Q100-2) (C_ZAP= 100 pF, R_ZAP= 1500 Ω), and the

Machine Model (MM) (C_ZAP= 200 pF, R_ZAP= 0 Ω.

2. 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.

3. 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.

4. Per JEDEC51-8 Standard for Multilayer PCB

5. Theoretical thermal resistance is from the die junction to the exposed pad.

34845

Analog Integrated Circuit Device Data

4

Freescale Semiconductor

ELECTRICAL CHARACTERISTICS

STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS

Table 3. Static and Dynamic Electrical Characteristics

Characteristics noted under conditions V_IN= 12 V, V_OUT= 35 V, I_LED= 30 mA, f_S= 600 kHz, f_PWM= 600 Hz - 40°C ≤ T_A

≤

85°C, unless otherwise noted. Typical values noted reflect the approximate parameter means at T_A= 25°C under nominal

conditions, unless otherwise noted.

Characteristic

Symbol

Min

Typ

Max

Unit

SUPPLY

Supply Voltage

V_IN

5.0

-

10

21

10

V

Supply Current when in Shutdown Mode

EN = Low, PWM = Low

I_SHUTDOWN

μA

2.0

Supply Current when Operational Mode

Boost = Pulse Skipping, Channels = 1% of Duty Cycle

EN = High, PWM = Low

I_OPERATIONAL

mA

-

5.0

-

6.5

4.4

Under-voltage Lockout

V_INRising

UVLO

UVLO_HYST

V_DC1

V

4.0

Under-voltage Hysteresis

V_INFalling

-

0.25

2.5

-

VDC1 Voltage⁽⁶⁾

C_VDC1= 2.2 μF

VDC2 Voltage⁽⁶⁾(V_INbetween 7.0 and 21 V)

2.4

5.7

2.6

6.3

V_DC2

C_VD2C= 2.2 μF

6.0

BOOST

Output Voltage Range⁽⁷⁾

VIN = 5.0 V

V_OUT1

V_OUT2

8.0

24

-

43

60

V

A

VIN = 21 V

Boost Switch Current Limit

I_{BOOST_LIMIT}

34845, 34845A

34845B

1.9

2.1

-

2.1

2.35

10

2.3

2.6

-

Boost Switch Current Limit Timeout

RDSON of Internal FET

I_DRAIN= 1.0 A

t_{BOOST_TIME}

R_DSON

ms

mΩ

-

300

520

1.0

500

-

Boost Switch Off state Leakage Current

V_SWA,SWB= 60 V

I_{BOOST_LEAK}

VOUT_LEAK

EFF_BOOST

μA

%

-

Feedback pin Off-state Leakage Current

V_OUT= 60 V

Peak Boost Efficiency⁽⁸⁾

V_OUT= 33 V, RL = 330 Ω

90

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: f_SW= 600 kHz, V_IN= 12 V, V_OUT= 33 V and R_L= 330 Ω. The following

external components are used: L = 10 μH DCR = 0.1 Ω, C_OUT= 3x1 μF (ceramic), Schottky diode V_F= 0.35 V.

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

5

ELECTRICAL CHARACTERISTICS

STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS

Table 3. Static and Dynamic Electrical Characteristics (continued)

Characteristics noted under conditions V_IN= 12 V, V_OUT= 35 V, I_LED= 30 mA, f_S= 600 kHz, f_PWM= 600 Hz - 40°C ≤ T_A

≤

85°C, unless otherwise noted. Typical values noted reflect the approximate parameter means at T_A= 25°C under nominal

conditions, unless otherwise noted.

Characteristic

Symbol

Min

Typ

Max

Unit

BOOST (CONTINUED)

Line Regulation

I_LED/V_IN

%/V

V_IN= 7.0 V to 21 V, I_CH= 30 mA

-0.2

-

0.2

Load Regulation

I_LED/V_LED

V_LED= 24 V to 40 V (all Channels), I_CH= 30 mA

Minimum Duty Cycle

D_MIN

D_MAX

-

10

90

15

-

%

V

Maximum Duty Cycle

88

OVP Internally Fixed Value

(no external voltage resistor divider)

V_{OVP_INT}

56

60

64

OVP Programming Range⁽⁹⁾

V_{OVP_EXT}

V

(set through an external resistor divider)

15

6.3

-

60

7.5

-

OVP Reference Voltage

OVP Sink Current

V_{REF_OVP}

I_{SINK_OVP}

f_S

6.9

0.2

V

μA

Switching Frequency

kHz

34845

540

600

1200

300

3.0

-

660

34845A

34845B

1080

1320

270

330

Soft Start Time (Fs=600 kHz, 100% PWM duty)

t_SS

-

ms

V

Soft Start VOUT Overshoot (Fs=600 kHz, 100% PWM duty)

Boost Switch Rise Time

SS_

OVP

VOUT

BOOST_t_R

BOOST_t_F

A_CSA

8.0

6.0

9.0

200

100

-

ns

Boost Switch Fall Time

Current sense Amplifier Gain

OTA Transconductance

G_M

μS

μA

Transconductance Sink and Source Current Capability

Slope Compensation

I_SS

V_SLOPE

V/μs

34845

-

0.52

0.73

0.22

-

34845A

34945B

LED DRIVER

LED Driver Sink Current

I_LED

mA

V

R_ISET= 51 kΩ 0.1%, PWM = 3.3 V

R_ISET= 5.1 kΩ 0.1%, PWM = 3.3 V

2.88

29.4

3.0

30

3.12

30.6

ISET Pin Voltage

V_ISET

R_ISET= 5.1 kΩ 0.1%

2.011

0.675

2.043

0.75

2.074

0.825

Regulated Minimum Voltage Across LED Drivers

Pulse Width > 400ns

V_MIN

V

LED Current Channel to Channel Tolerance

10 mA ≤ I_LED≤ 30 mA

I_TOLERANCE

%

-2.0

-4.0

-

2.0

4.0

3.0 mA ≤ I_LED< 10 mA

Notes

9. The OVP level must be set 5.0 V above the worst-case LED string voltage.

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

6

ELECTRICAL CHARACTERISTICS

STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS

Table 3. Static and Dynamic Electrical Characteristics (continued)

Characteristics noted under conditions V_IN= 12 V, V_OUT= 35 V, I_LED= 30 mA, f_S= 600 kHz, f_PWM= 600 Hz - 40°C ≤ T_A

≤

85°C, unless otherwise noted. Typical values noted reflect the approximate parameter means at T_A= 25°C under nominal

conditions, unless otherwise noted.

Characteristic

LED DRIVER (CONTINUED)

Symbol

Min

Typ

Max

Unit

Off State leakage Current, All Channels

V_CH= 45 V

I_{CH_LEAK}

μA

-

1.0

LED Channels Rise and Fall Time

t_R/t_F

O_FDV

S_FDV

-

50

-

75

ns

V

LED Open Protection, Channel Disabled if V_CH≤ O_FDV

LED Short Protection Voltage, Channel Disabled if V_CH≥ S_FDV

(channel on time ≥ 10 μs)

0.55

V

6.5

7.0

7.5

FAIL PIN

Off State Leakage Current

V_FAIL= 5.5 V

I_{FAIL_LEAK}

μA

-

5.0

0.4

On State Voltage Drop

I_SINK= 4.0 mA

V_OL

V

OVER-TEMPERATURE SHUTDOWN

Over-temperature Threshold (shutdown mode)

OTT_SHUTDOWN

PWM_CONTROL

t_{PWM_IN}

°C

%

Rising

150

-

165

25

-

Hysteresis

PWM INPUT

PWM Dimming Mode LED Current Control

PWM = 3.3 V, f_PWM= 600 Hz 10% duty;

PWM = 3.3 V, f_PWM= 600 Hz 50% duty

PWM = 3.3 V, f_PWM= 600 Hz 100% duty

9.9

49.5

-

10

50

10.1

50.5

-

100

Input Minimum Pulse PWM Pin (V

Start-up (Wake Mode)

=3.3 V)

μs

PWM

1.6

-

0.2

-

Operational (Wake Mode)

Start-up (Enable Mode)

-

0.4

-

Operational (Enable Mode)

0.2

-

Input Frequency Range for PWM Pin

WAKE

f_PWM

DC

100

kHz

ms

Shutdown Mode Timeout

LOGIC INPUTS (PWM)

Input Low Voltage

t_SHUTDOWN

27

30

33

V_ILL

V_IHL

I_SINK

-0.3

1.5

-

0.5

5.5

1.0

V

Input High Voltage

Input Current

-1.0

μA

LOGIC INPUTS (EN)

Input Low Voltage

V_ILL

V_IHL

I_SINK

-0.3

2.1

-

0.5

21

10

V

Input High Voltage

Input Current (V_EN= 12 V)

LOGIC INPUTS (WAKE)

Input Low Voltage

6.0

μA

V_ILL

V_IHL

I_SINK

-0.3

2.1

-

0.5

5.5

1.0

V

Input High Voltage

Input Current

-1.0

μA

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

7

PIN CONNECTIONS

STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS

PIN CONNECTIONS

TRANSPARENT

TOP VIEW

24

23

22

21

20

19

VIN

PGNDB

SWB

WAKE

COMP

PWM

ISET

18

17

16

15

14

13

1

2

3

4

5

6

EP GND

SWA

FAIL

PGNDA

EN

GND

7

8

9

10

11

12

Figure 3. 34845 Pin Connections

Definition

Table 4. 34845 Pin Definitions

Pin Number Pin Name

1

VIN

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

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).

PGNDB

SWB

3

4

SWA

5

6

PGNDA

EN

7 - 12

13, 19, 21

LED string connections 1 to 6. LED current drivers. Each line has the capability of driving up to 30 mA.

CH1 - CH6

GND

Ground Reference for all internal circuits other than the Boost FET. The Exposed Pad (EP) should be used for

thermal heat dissipation.

14

Fault detected pin (open drain):

FAIL

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.

15

16

17

ISET

PWM

COMP

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.

18

20

22

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.

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.

VDC1

OVP

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

Analog Integrated Circuit Device Data

Freescale Semiconductor

8

PIN CONNECTIONS

STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS

Table 4. 34845 Pin Definitions (continued)

Pin Number Pin Name

Definition

23

6.0 V internal voltage decoupling. This pin is for internal use only, and not to be used for other purposes. A

VDC2

capacitor of 2.2 μF should be connected between this pin and ground.

24

Boost voltage output feedback.

VOUT

EP

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.

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.

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

FUNCTIONAL DEVICE OPERATION

Figures 4 and 5 illustrate the two different power up

conditions.

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.

VIN

EN

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.

PWM

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.

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

Analog Integrated Circuit Device Data

Freescale Semiconductor

10

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

LED DRIVER

PWM

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.

5V

VIN

2ms

Boost

Soft Start

UVLO Rising

LED ERROR DETECT

VOUT

VIN ramp

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.

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.

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 μs, the SFDV circuit will not disable

any of the channels, regardless of the voltage across them.

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).

All the LED errors can be cleared by recycling the EN pin

or applying a complete power-on-reset (POR).

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.

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 V_OUT. The details of

the suggested compensation network are shown in Figures

10 and 11.

OVER-TEMPERATURE SHUTDOWN AND

TEMPERATURE CONTROL CIRCUITS

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 I_OCP. 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 34845 includes over-temperature protection. If the

internal temperature exceeds the over-temp threshold

OTT_SHUTDOWN, then the device shuts down all functions.

Once the temperature falls below the low level threshold, the

device is re-enabled.

The boost also includes a soft start circuit. Each time the

IC comes out of shutdown mode, the soft start period lasts for

t_SS

.

FAIL PIN

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

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 Over-

current time-out, the EN pin or a POR must be cycled/

executed to restart the part.

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

11

TYPICAL PERFORMANCE CURVES

INTRODUCTION

TYPICAL PERFORMANCE CURVES

100.0

90.0

80.0

70.0

60.0

50.0

40.0

30.0

20.0

10.0

Vin=9V

Fs = 600kHz

L=10uH, 68mOhm (IHLP2525CZER100M01)

Schottky 5A, 100V (PDS5100HDICT-ND)

COUT = 2x2.2µF

FPWM=25kHz

Load = 9 LEDs, 20mA/channel

VLED = 27.8V, ±0.5V /channel

0.0

0

10

20

30

40

50

60

70

80

90

100

Duty Cycle (%)

Figure 6. Typical System Efficiency vs Duty Cycle (FPWM=25kHz)

Chablis ILED Dimming Linearity (FPWM=25kHz)

2.000%

1.500%

1.000%

0.500%

0.000%

-0.500%

-1.000%

-1.500%

-2.000%

(-) Mismatch @25°C

(+) Mismatch @ 25°C

1

10

100

% Duty cycle

Figure 7. Typical ILED Dimming Linearity (FPWM=25kHz)

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

12

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)

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

13

TYPICAL APPLICATIONS

INTRODUCTION

TYPICAL APPLICATIONS

10 uH

VIN

LED

LEG

LED

LEG

LED

LEG

LED

LEG

LED

LEG

60 V, 1A

1

2

LEG 3

4

5

6

2 .2uF

2.2 uF

10uf

25V

100 pF

100pF

100 pF

Cap s should be l ocated

as c lose as poss ible to

VIN

1

100 pF

SW A

SW B

4

3

the MC 34845 de vice

0. 1uf

VD C 1

20

VOU T

PGN D

100 pF

24

2

VD C 2

23

2 .2uF

2. 2uF

5

kΩ

5.6 M O

100p F

10 V

OVP

22

kΩ

MO

1

CH1

CH2

7

8

2 .2nF

MC34845

COMP

17

CH3

CH4

9

10

11

22 kkΩO

1 0 kkOΩ

56 pF

EN

CH5

6

CH6

12

Cont rol

Un it

PWM

16

WAKE

18

15

FAIL

14

13

GND

EP

21

GND

kΩ

7.6 5 KO

0.1 %

Figure 10. Typical Application Circuit for Single Wire Control, f_S= 600 KHz

(V_IN= 9.0 V, I_LED/channel = 20 mA/channel, 12 LEDs/channel, OVP = 45 V, V_PWM= 3.3 V)

4 .7uH

VIN

LED

LEG

LED

LEG

LED

LEG

LED

LEG

LED

LEG

60 V, 1A

1

2

LEG 3

4

5

6

2 .2uF

2.2 uF

10uf

25V

100 pF

100pF

100 pF

Cap s should be l ocated

as c lose as poss ible to

VIN

100 pF

SW A

SW B

1

4

3

the MC 34845 de vice

0. 1uf

VD C 1

VD C 2

VOU T

PGN D

100 pF

20

23

24

2

2 .2uF

10 V

2. 2uF

10 V

5

kΩ

5.6 M O

100p F

OVP

22

kΩ

MO

1

CH1

CH2

7

8

2 .2nF

MC34845A

COMP

56 pF

17

CH3

CH4

9

10

11

kΩ

1 0 kO

22 kkΩO

CH5

EN

6

CH6

12

Cont rol

Un it

PWM

16

WAKE

18

15

FAIL

14

13

GND

EP

21

GND

7.6 5 KkΩO

0.1 %

Figure 11. Typical Application Circuit for Single Wire Control, f_S= 1.2 MHz

(V_IN= 9.0 V, I_LED= 20 mA/channel, 12 LEDs/channel, OVP = 45 V, V_PWM= 3.3 V)

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

14

TYPICAL APPLICATIONS

INTRODUCTION

33 u H

VIN

LED

LEG

LED

LEG

LED

LEG

LED

LEG

LED

LEG 5

LED

LEG

80 V, 1A

1

2

3

4

6

2.2uF

2.2uF 2.2 u F

10 u f

25 V

100 pF

10 0 pF

Caps s hould be located

as cl os e a s p os si ble to

the MC 34 84 5 de vic e

100 pF

VI N

SWA

1

4

3

SWB

0. 1 uf

VDC1

VDC2

VOUT

10 0 pF

20

23

24

2

PGND

2.2uF

10V

2.2uF

10 V

5

1 MO

100 pF

OVP

22

16 2 kO

CH1

CH2

7

8

8.2nF

MC34845 B

COMP

150pF

17

CH3

CH4

9

3.3 kO

10

CH5

CH6

11

12

EN

PWM

WAKE

6

Cont rol

Unit

16

18

15

FAIL

14

13

GND

EP

21

GND

7. 65 K O

0. 1 %

Figure 12. Typical Application Circuit for Single Wire Control, f_S= 300 kHz

(V_IN= 8.0 V, I_LED= 20 mA/channel, 14 LEDs/channel, OVP = 49 V, V_PWM= 3.3 V)

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

15

TYPICAL APPLICATIONS

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:

D

1 – D

I

= I_OUT

×

------------

RMS – C_OUT

V

_OUT+ V_D– V_IN

D = ----------------------------------------------

_OUT+ V_D– V_SW

V

The average input current depends directly on the output

current when the internal switch is off.

Note that before calculating the network compensation, all

boost converter components need to be known.

I_OUT

I_{IN – AVG}= ------------

1 – D

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.

Inductor

For calculating the Inductor, consider the losses of the

internal switch and winding resistance of the inductor:

2

(V_IN– V_SW– (I_{IN – AVG}× R_INDUCTOR)) × D

L = -----------------------------------------------------------------------------------------------------------------

I_{IN – AVG}× r × F_SW

V

× (1 – D)

OUT

= --------------------------------------------

f

RHPZ

I

× 2π × L

OUT

It is important to look for an inductor rated at least for the

maximum input current:

V

× (V

– V

)

IN

OUT

× V

IN

OUT

I

= I

+ ---------------------------------------------------------

IN – MAX

IN – AVG

The crossover frequency must be set much lower than the

location of the Right half plane zero:

2 × L × F

SW

Input Capacitor

f_RHPZ

f_CROSS= --------------

5

The input capacitor should handle at least the following

RMS current.

Since our system has a fixed slope compensation, RCOMP

should be fixed for all configurations, i.e. RCOMP = 8.2 Kohm

V

× (V

– V

)

⎛

⎜

⎝

⎞

⎟

⎠

IN

OUT

× V

IN

OUT

---------------------------------------------------------

I

=

× 0.3

RMS – C

2 × L × F

C_COMP1and C_COMP2should be calculated as follows:

IN

SW

2

C

= ----------------------------------------------------------------

COMP1

R

Output Capacitor

2π × f

× COMP

CROSS

For the output capacitor selection the transconductance

should be taken in consideration.

G

M

C

= -----------------------------

COMP2

6.28 × F

SW

R

× 5 × G × I

× L

COMP

M

OUT

× 0.35

C

= -------------------------------------------------------------------------------

OUT

The recommended values of these capacitors for an

acceptable performance of the system in different operating

conditions are Ccomp1=2.2nF and Ccomp2=56pF.

(1 – D) × V

OUT

The output voltage ripple (ΔV_OUT) 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.

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. 10kΩ and 39kΩ.

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.

V

× ΔV

× F

× L

OUT

× (1 – D)

SW

ESR

= --------------------------------------------------------------------------

C_OUT

V

OUT

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.

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

16

TYPICAL APPLICATIONS

COMPONENTS CALCULATION

Variable definition

I_RMS-COUT= RMS current for output capacitor

L = Inductor.

D = Duty cycle

R_INDUCTOR= Inductor winding resistor

F_SW= Boost switching frequency

C_OUT= Output capacitor

V_OUT= Output voltage

V_D= Diode voltage

V_IN= Input voltage

R_COMP= Compensation resistor

G_M= OTA transconductance

V_SW= Internal switch voltage drop.

ΔV_OUT= Output voltage ripple

I_IN-AVG= Average input current = I_L-AVG

I_OUT= Output current

ESR_COUT= ESR of the output capacitor

f_RHPZ= Right half plane zero frequency

f_CROSS= Crossover frequency

C_COMP1= Compensation capacitor

C_COMP2= Shunt compensation capacitor

I_IN-MAX= Maximum input current

r = Current ripple ratio at the inductor = ΔI_L/ I_L-AVG

I_RMS-CIN= RMS current for the input capacitor

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

17

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

Analog Integrated Circuit Device Data

Freescale Semiconductor

18

PACKAGING

PACKAGE DIMENSIONS

EP SUFFIX

24-PIN

98ASA00087D

REVISION A

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

19

PACKAGING

EP SUFFIX

24-PIN

98ASA00087D

REVISION A

34845

Analog Integrated Circuit Device Data

Freescale Semiconductor

20

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MC34845

Rev. 2.0

9/2009