Datasheet MP2481DH Datasheet (MPS) [ru]

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Page 1

MP2481

White LED Driver

36V, 1.2A, 1.4MHz

The Future of Analog IC Technology

DESCRIPTION

The MP2481 is a 36V, 1.2A, white LED driver suitable for either step-down or inverting step-up/down applications. It achieves 1.2A peak output current over a wide input supply range with excellent load and line regulation. Current mode operation provides fast transient response and eases loop stabilization. Fault condition protection includes thermal shutdown, cycle-by-cycle peak current limiting, input over voltage protection, open strings protection and output short circuit protection. The MP2481 incorporates both DC and PWM dimming onto a single control pin. The separate input reference ground pin allows for direct enable and/or dimming control for a positive to negative power conversion. The MP2481 requires a minimum number of readily available standard external components and is available in 8-pin MSOP8E package.

EVALUATION BOARD REFERENCE

Board Number Mode

EV2481-H-00A Step-down

EV2481-H-01A Step-up/down

FEATURES

 1.2A Maximum Output Current  Unique Step-up/down Operation (Buck-

Boost Mode)

 Wide 4.5V to 36V Operating Input Range for

Step-Down Applications (Buck Mode)

 0.30 Internal Power MOSFET Switch  Fixed 1.4MHz Frequency  Analog and PWM Dimming  0.2V Reference Voltage  Up to 95% Efficiency  5A Shutdown Mode  No minimum LED required  Stable with Low ESR Output Ceramic

Capacitors

 Cycle-by-Cycle Over Current Protection  Thermal Shutdown Protection  Open Strings Protection  Input Over Voltage Protection  Output Short Circuit Protection  Available in 8-Pin MSOP8E Package

APPLICATIONS

 General LED Illuminations  LCD Backlight Panels  Handheld Computers  Automotive Internal Lighting  Portable Multimedia Players  Portable GPS Devices

All MPS parts are lead-free and adhere to the RoHS directive. For MPS green status, please visit MPS website under Quality Assurance. “MPS” and “Th Future of Analog IC Technology” are Trademarks of Monolithic Powe Systems, Inc.

TYPICAL APPLICATION (STEP-UP/DOWN APPLICATION)

Efficiency vs.

4.5V-36V

VIN

OFF

DC or PWM INPUT

VDD OVP

EN/DIM

INGND

MP2481

VSS

BST

Cbs

3 series, 9 paralleled

Step-up/down

4 series,400mA

3 series,400mA

3 series,9 paralleded,180mA total

EFFICIENCY (%)

0 5 10 15 20 25 30

INPUT VOLTAGE (V)

Input

Application

Voltage

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MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

ORDERING INFORMATION

Part Number* Package Top Marking

MP2481DH

MSOP8E

2481D

* For Tape & Reel, add suffix –Z (e.g. MP2481DH–Z).

For RoHS compliant packaging, add suffix –LF (e.g. MP2481DH–LF–Z)

PACKAGE REFERENCE

TOP VIEW

VDD

VSS

OVP

EXPOSED PAD

ON BACK SIDE

* Do not Connect to Input Ground (INGND)

for Boost, Buck-Boost applications

BST

INGND

EN/DIM

ABSOLUTE MAXIMUM RATINGS

(1)

Supply Voltage VDD – VSS............................. 40V

– VSS............................. –0.3V to VIN + 0.3V

...................................................... VSW + 6V

BST

– VSS......................................–0.3V to +6V

OVP

– V

DIM

INGND

Continuous Power Dissipation (T

....................................–0.3V to +6V

INGND

...................................–0.3V to +6V

INGND

– VSS....................................–0.3V to 40V

= +25°C)

(2)

………………………………………………....2.3W

Junction Temperature...............................150C

Lead Temperature ....................................260C

Storage Temperature.............. –65C to +150C

Recommended Operating Conditions

(3)

Supply Voltage VDD – VSS.................4.5V to 36V

Operating Junct. Temp (T

)..... –40C to +125C

Thermal Resistance

(4)

θJC

MSOP8E (Exposed Pad) ........55 ...... 12... C/W

Notes:

1) Exceeding these ratings may damage the device.

2) The maximum allowable power dissipation is a function of the maximum junction temperature T ambient thermal resistance 

. The maximum allowable continuous power dissipation at

any ambient temperature is calculated by P (MAX)-TA)/JA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal shutdown circuitry protects the device from permanent damage.

3) The device is not guaranteed to function outside of its operating conditions.

4) Measured on JESD51-7, 4-layer PCB.

(MAX), the junction-to-

, and the ambient temperature

(MAX) = (T

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MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

ELECTRICAL CHARACTERISTICS

VIN = 12V, TA = +25C, all voltages with respect to VSS, unless otherwise noted.

Parameters Symbol Condition Min Typ Max Units

Feedback Voltage VFB

4.5V  V

 36V

Feedback Current IFB VFB = 0.2V 0.2 A Switch-On Resistance

(5)

DS(ON)

0.30 

Switch Leakage VEN = 0V, VSW = 0V 10 A Switch Current Limit

(5)

2.0 A Oscillator Frequency fSW VFB = 0.1V 1.0 1.4 1.8 MHz Fold-back Frequency V

< 0.4V 120 kHz

OVP

Maximum Duty Cycle VFB = 0.1V 89 % Minimum On-Time

(5)

100 ns

Under Voltage Lockout Threshold Rising 3.1 3.4 3.7 V Under Voltage Lockout Threshold

Hysteresis

EN Input Current

480 mV

VEN = 2V 2.0 V

= 0V 0.1

EN OFF Threshold (w/Respect to INGND) VEN Falling 0.4 V EN ON Threshold (w/Respect to INGND) VEN Rising 0.7 V Supply Current (Quiescent) I Thermal Shutdown

(5)

150 °C Open LED OV Threshold V Open LED OV Hysteresis V

Note:

5) Guaranteed by design.

OVP, th

OVP, hys

VEN = 2V, VFB = 1V 0.6 1.1 mA

1.23 V

0.1 V

0.187 0.203 0.219 V

A

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MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

PIN FUNCTIONS

Pin # Name Description

1 VDD

2 VSS

3 OVP

4 FB

5 EN/DIM

6 INGND Input Ground Reference. This pin is the reference for the EN/DIM signal.

7 BST

8 SW

Supply Voltage. The MP2481 operates from a +4.5V to +36V unregulated input (with respect to VSS). C1 is needed to prevent large voltage spikes from appearing at the input.

Power Return Pin. Connect to the lowest potential in the circuit, which is typically the anode of the Schottky rectifier. This pin is the voltage reference for the regulated output voltage. For this reason care must be taken in its layout. This node should be placed outside of the D1 to C1 ground path to prevent switching current spikes from inducing voltage noise into the part. The exposed pad is also connected to this pin.

Over Voltage Protection Pin. Use one external resistor voltage divider to program OVP threshold. When the OVP pin voltage (with respect to VSS) is lower than 0.4V, the chip frequency will be folded back. Program the OVP pin voltage from 0.4V to 1.23V for normal operation. When the OVP pin voltage reaches the shutdown threshold 1.23V, the switch will be turned off

LED Current Feedback Input. MP2481 regulates the voltage across the current sensing resistor between FB and VSS. Connect the current sensing resistor from the bottom of the LED strings to VSS. The FB pin is connected to the bottom of the LED strings. The regulation voltage is 0.2V.

On/Off Control Input and Dimming Command Input. A voltage greater than 0.7V will turn on the chip. When the EN/DIM pin voltage (with respect to INGND) rises from 0.7V to 1.4V, the LED current will change from 0% to 100% of the maximum LED current. To use PWM dimming, apply a 100Hz to 1kHz square wave signal with amplitude greater than 1.4V to this pin.

Bootstrap. A capacitor is connected between SW and BST pins to form a floating supply across the power switch driver. This capacitor is needed to drive the power switch’s gate above the supply voltage.

Switch Output. SW is the source of the internal MOSFET switch. Connect to the power inductor and cathode of the Schottky rectifier.

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MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

TYPICAL PERFORMANCE CHARACTERISTICS

VIN=12V, I noted.

=1A, one 5W WLED, Step-down application (refer to Figure 3), unless otherwise

LED

10V/div.

200mV/div.

OUT

AC Coupled

200mV/div.

INDUCTOR

I 500mA/div.

V 10V/div.

INDUCTOR

I 500mA/div.

Steady State Operation

400ns/div

Short Circuit Protection

Short LED+ to INGND

10V/div.

PWM

5V/div.

OUT

2V/div.

LED

500mA/div.

100

EFFICIENCY (%)

PWM Dimming

PWM

=1kHz,D

PWM

=50%

Efficiency vs. Input Voltage

2 WLEDs in series,500mA

1 WLED,500mA

3 WLEDs in series,500mA

1 WLED,1A

10 20 30 40

INPUT VOLTAGE (V)

Open Load Protection

OUT

2V/div.

V 10V/div.

LED

I 1A/div.

LED Current vs. Analog Dimming Voltage

1.2

1.0

0.8

0.6

0.4

LED CURRENT (A)

0.2

0.4

ANALOG DIMMING VOLTAGE (V)

0.6 0.8 1.0 1.2 1.4 1.6 1.8

LED Current vs.

0.8

1.0

PWM Dimming Duty

PWM

=1kHz

1.2

1.0

0.8

0.6

0.4

LED CURRENT (A)

0.2

0.2 0.4 0.6

PWM Dimming Duty

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MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

TYPICAL PERFORMANCE CHARACTERISTICS (continued)

VIN=12V, I unless otherwise noted.

=180mA, 3 WLEDs in series, 9 strings, Step-up/down application (refer to Figure 4),

LED

10V/div.

AC Coupled

200mV/div.

INDUCTOR

500mA/div.

10V/div.

INDUCTOR

I 500mA/div.

Steady State Operation

400ns/div

Short Circuit Protection

Short LED+ to VSS

V 20V/div.

PWM

5V/div.

2V/div.

LED

200mA/div.

EFFICIENCY (%)

PWM Dimming

PWM

=1kHz,D

=50%

PWM

Efficiency vs. Input Voltage

4 series,400mA

3 series,400mA

3 series,9 paralleded,180mA total

0 5 10 15 20 25 30

INPUT VOLTAGE (V)

V 20V/div.

V 5V/div.

LED

I 200mA/div.

200

180

160

140

120

100

LED CURRENT (mA)

Open Load Protection

LED Current vs.Analog Dimming Voltage

0.4

0.6 0.8 1.0 1.2 1.4 1.6 1.8

ANALOG DIMMING VOLTAGE (V)

LED Current vs. PWM Dimming Duty

PWM

200

180

160

140

120

100

LED CURRENT (mA)

=1kHz

0 0.2 0.4 0.6

PWM Dimming Duty

0.8

1.0

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FUNCTION BLOCK DIAGRAM

MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

VDD

EN/DIM

INGND

VSS

ENABLE

DIMMING CONTROL

(VEN-0.7)/3.5

0.2V

POR&

REGULATOR

REFERENCE

SOFTSTART

4.0V

RAMP

GENERATOR

OVP

OSCILLATOR

1.4MHz/120KHz

27pF

+ +

1pF

ERROR

AMPLIFIER

REGULATOR

CURRENT LIMIT COMPARATOR

PWM

COMPARATOR

Figure 1—Function Block Diagram

CURRENT SENSE

x20

AMPLIFIER

DRIVER

+ +

1.2V

BST

VDD

OVP

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OPERATION

The MP2481 is a current mode regulator. The EA output voltage is proportional to the peak inductor current.

At the beginning of a cycle, M1 is off. The EA output voltage is higher than the current sense amplifier output, and the current comparator’s output is low. The rising edge of the 1.4MHz CLK signal sets the RS Flip-Flop. Its output turns on M1 thus connecting the SW pin and inductor to the input supply.

The increasing inductor current is sensed and amplified by the Current Sense Amplifier. Ramp compensation is summed to the Current Sense Amplifier output and compared to the Error Amplifier output by the PWM Comparator. When the sum of the Current Sense Amplifier output and the Slope Compensation signal exceeds the EA output voltage, the RS Flip-Flop is reset and M1 is turned off. The external Schottky rectifier diode (D1) conducts the inductor current.

If the sum of the Current Sense Amplifier output and the Slope Compensation signal does not exceed the EA output for a whole cycle, then the falling edge of the CLK resets the Flip-Flop.

The output of the Error Amplifier integrates the

voltage difference between the feedback and the

0.2V reference. The polarity is such that a FB pin voltage lower than 0.2V increases the EA output voltage. Since the EA output voltage is proportional to the peak inductor current, an increase in its voltage also increases current delivered to the output.

MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

Open Strings Protection

If LED strings are open, there is no voltage on the FB pin. The duty cycle increases until V(VDD)

- V(VSS) reaches to 38V or V(OVP) - V(VSS) reaches the shutdown threshold 1.23V. Then the top switch is kept off. It will be switching again when the voltage V(VDD) - V(VSS) and V(OVP) V(VSS) decreases sufficiently.

Dimming Control

The MP2481 allows both DC and PWM dimming. When V(EN/DIM) – V(INGND) is less than 0.4V, the chip is turned off. For analog dimming, when V(EN/DIM) – V(INGND) rises from 0.7V to 1.4V, the LED current will change from 0% to 100% of the maximum LED current. If V(EN/DIM) – V(INGND) is higher than 1.4V, maximum LED current is generated. If a PWM signal is used, its amplitude V (EN/DIM) – V (INGND) must exceed

1.4V.

The MP2481 is designed with an internal EN shut-down delay (see Figure 2). If EN is pulled down, the FB reference drops to zero immediately and the LED current decreases. But the IC keeps internal logic on for about 2.5ms. In this period, the IC may switch with very short pulses in pulse-skipping mode, while the LED current is zero since the FB reference is zero. It has benefit that the IC will start up more quickly without delay when next PWM duty comes. This function offers the possibility to extend the PWM dimming frequency and also the minimum PWM on time for further dimming depth.

Figure 2— Internal EN Shut-down Delay Function Waveform Diagram

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APPLICATION INFORMATION



Setting the LED Current

The external resistor is used to set the maximum LED current (see the schematic on front page) through the use of the equation:

SENSE

0.200V

Setting the OVP point

To make sure the chip functions properly, the Over Voltage Protection (OVP) resistor divider must be set with proper value, the recommended OVP point is about 1.3~1.5 times higher than the output voltage for normal operation and over voltage protection.

Selecting the Inductor

(Step-Down Applications, see Figure 3)

A 3.3µH to 10µH inductor with a DC current rating of at least 25% higher than the maximum load current is recommended for most applications. For highest efficiency, the inductor’s DC resistance should be less than 200m. Refer to Table 1 for suggested surface mount inductors. For most designs, the required inductance value can be derived from the following equation.



Where V the output voltage, I

is the lowest input voltage, V

is the inductor ripple

current.

Choose the inductor ripple current to be 30% of the maximum load current. The maximum inductor peak current is calculated from:

LOAD)MAX(L

LED





)VV(V

OUTINOUT

fIV



SWLIN

OUT



MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

If the calculation of above equations results in an inductance greater than 10uH, a 10uH inductor is still preferred.

Under light load conditions below 100mA, a larger inductance is recommended for improved efficiency.

Also note that the maximum recommended load current is 1A if the duty cycle exceeds 35%.

(Step up/Down Applications, see Figure 4)

Operation at step-up/down mode, the recommended inductance value can be derived from the following equation:

-V V



OUT IN

IN OUT L SW



When V

(V - V )

is the lowest input voltage, V

output voltage (negative), I

is the inductor

OUT

is the

ripple current. For most step-up/down applications, a 3.3uH to 22uH with suitable DC current rating is recommended. See Table 1 for suggested inductors.

Selecting the Input Capacitor

The input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. The input capacitor impedance at the switching frequency should be less than the input source impedance to prevent high frequency switching current from passing through the input. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. For most applications, a 4.7µF capacitor is sufficient.

Table 1—Suggested Surface Mount Inductors

Manufacturer Part Number Inductance(µH) Max DCR(Ω)

Toko A921CY-4R7M 4.7 0.027 1.66 6 x 6.3 x 3

Sumida CDRH4D28C/LD 4.7 0.036 1.5 5.1 x 5.1 x 3

Wurth Electronics 7440530047 4.7 0.038 2.0 5.8 x 5.8 x 2.8

Current

Rating (A)

Dimensions

L x W x H (mm

)

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Selecting the Output Capacitor

MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

PC Board Layout Considerations

The output capacitor keeps the output voltage ripple small and ensures feedback loop stability. The output capacitor impedance should be low at the switching frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended for their low ESR characteristics. For most applications, a 2.2µF ceramic capacitor will be sufficient.

The high current paths (VSS, VDD and SW) should be placed very close to the device with short, direct and wide traces. The input capacitor needs to be as close as possible to the VDD and VSS pins. The external feedback resistors should be placed next to the FB pin. Keep the switch node traces short and away from the feedback network.

Page 11

TYPICAL APPLICATION CIRCUITS

6V-36V

VIN

VDD OVP

MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

BST

C3 10nF

OFF

DC or PWM INPUT

4.5V-36V

VIN

OFF

DC or PWM INPUT

EN/DIM

INGND

MP2481

VSS

D1 B140

LED1

0.2 1%

Figure 3—Step-Down White LED Driver Application

VDD OVP

MP2481

EN/DIM

INGND

VSS

BST

C3 10nF

D1 B140

3 series, 9 paralleled

Figure 4—Step-up/down White LED Driver Application

1.1

VDD

EN/DIM

INGND

OVP

MP2481

VSS

BST

C3 10nF

D1 B140

3 series, 9 paralleled

1.1

100

4.5V-7.5V

VIN

OFF

DC or PWM INPUT

Figure 5—Optional Step-up White LED Driver Application

Page 12

PACKAGE INFORMATION

MP2481 –36V, 1.2A, 1.4MHz WHITE LED DRIVER

MSOP8E W/ EXPOSED PAD

PIN 1 ID

(NOTE 5)

0.010(0.25)

0.014(0.35)

0.030(0.75)

0.037(0.95)

0.114(2.90)

0.122(3.10)

TOP VIEW

0.0256(0.65)BSC

0.000(0.00)

0.006(0.15)

0.114(2.90)

0.122(3.10)

0.043(1.10)MAX

SEATING PLANE

0.187(4.75)

0.199(5.05)

GAUGE PLANE

0.010(0.25)

0o-6

0.087(2.20)

0.099(2.50)

0.062(1.58)

0.074(1.88)

Exposed Pad

BOTTOM VIEW

0.004(0.10)

0.016(0.40)

0.026(0.65)

0.008(0.20)

0.040(1.00)

0.016(0.40)

FRONT VIEW

0.100(2.54)

0.181(4.60)0.075(1.90)

0.0256(0.65)BSC

NOTE:

1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN BRACKET IS IN MILLIMETERS.

2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH, PROTRUSION OR GATE BURR.

3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSION.

4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.004" INCHES MAX.

5) PIN 1 IDENTIFICATION HAS HALF OR FULL CIRCLE OPTION.

6) DRAWING MEETS JEDEC MO-187, VARIATION AA-T.

7) DRAWING IS NOT TO SCALE.

SIDE VIEW

RECOMMENDED LAND PATTERN

NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third

party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications.

Page 13

Datasheet MP2481DH Datasheet (MPS) [ru]

Specifications and Main Features

Frequently Asked Questions

User Manual