National Semiconductor LM5021 Technical data

LM5021 AC-DC Current Mode PWM Controller

June 2005

General Description

The LM5021 off-line pulse width modulation (PWM) controller contains all of the features needed to implement highly efficient off-linesingle-ended flybackand forward powerconverters using current-mode control. The LM5021 features include an ultra-low (25 µA) start-up current, which minimizes power losses in the high voltage start-up network. A skip cycle mode reduces powerconsumption with light loads for energy conserving applications (ENERGY STAR CECP, etc.). Additional features include under-voltage lockout, cycle-by-cycle current limit, hiccup mode overload protection, slope compensation, soft-start and oscillator synchronization capability. This high performance 8-pin IC has total propagation delays less than 100nS and a 1MHz capable oscillator that is programmed with a single resistor.

Simplified Application Diagram

Features

n Ultra Low Start-up Current (25 µA maximum) n Current Mode Control n Skip Cycle Mode for Low Standby Power n Single Resistor Programmable Oscillator n Synchronizable Oscillator n Adjustable Soft-start n Integrated 0.7A Peak Gate Driver

n Direct Opto-Coupler Interface n Maximum Duty Cycle Limiting (80% for LM5021-1 or

50% for LM5021-2)

n Slope Compensation for (LM5021-1 Only) n Under Voltage Lockout (UVLO) with Hysteresis n Cycle-by-Cycle Over-Current Protection n Hiccup Mode for Continuous Overload Protection n Leading Edge Blanking of Current Sense Signal n Packages: MSOP-8 or MDIP-8

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Connection Diagram

LM5021

Top View

MSOP-8 and MDIP-8

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Ordering Information

Order Number Description Package Type Supplied As

LM5021MM-1 80% Duty Cycle Limit MSOP-8 1000 Units on Tape and Reel

LM5021MMX-1 80% Duty Cycle Limit MSOP-8 3500 Units on Tape and Reel

LM5021NA-1 80% Duty Cycle Limit MDIP-8 40 Units per Rail

LM5021MM-2 50% Duty Cycle Limit MSOP-8 1000 Units on Tape and Reel

LM5021MMX-2 50% Duty Cycle Limit MSOP-8 3500 Units on Tape and Reel

LM5021NA-2 50% Duty Cycle Limit MDIP-8 40 Units per Rail

Pin Description

PIN NAME DESCRIPTION APPLICATION INFORMATION

1 COMP Control input for the Pulse Width Modulator

and Hiccup comparators.

2 VIN Input voltage. Input to start-up regulator. The VIN pin is clamped at

3 VCC Output of a linear bias supply regulator.

Nominally 8.5V.

4 OUT MOSFET gate driver output. High current output to the external MOSFET gate input

5 GND Ground return. 6 CS Current Sense input. Current sense input for current mode control and

7 RT / SYNC Oscillator timing resistor pin and

synchronization input.

8 SS Soft-start / Hiccup time An external capacitor and an internal 22 µA current

COMP pull-up is provided by an internal 5K resistor which may be used to bias an opto-coupler transistor.

36V by an internal zener diode. VCC provides bias to controller and gate drive sections

of the LM5021. An external capacitor must be connected from this pin to ground.

with source/sink current capability of 0.3A and 0.7A respectively.

over-current protection. Current limiting is accomplished using a dedicated current sense comparator. If the CS comparator input exceeds 0.5 Volts the OUT pin switches low for cycle-by-cycle current limit. CS is held low for 90ns after OUT switches high to blank the leading edge current spike.

An external resistor connected from RT to GND sets the oscillator frequency. This pin will also accept synchronization pulses from an external clock.

source set the soft-start ramp. The soft -start capacitor controls both the soft-start rate and the hiccup mode period.

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LM5021

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

ESD Rating (Note 2)

Human Body Model 2kV Storage Temperature -65˚C to +150˚C Operating Junction Temperature +150˚C

VIN to GND -0.3V to 30V VIN Clamp Continuous Current 5mA

Operating Ratings (Note 1)

CS to GND -0.3V to 1.25V RT to GND -0.3V to 5.5V All other pins to GND -0.3V to 7.0V

Electrical Characteristics Specifications in standard type face are for T

type apply over the full Operating Junction Temperature Range. Unless otherwise specified: V

VIN Voltage (Note 5) 8V to 30V Junction Temperature -40˚C to +125˚C

= +25˚C and those in boldface

= 15V, RT= 44.2KΩ.

(Note 3)

Symbol Parameter Conditions Min Typ Max Unit

STARTUP CIRCUIT

Start Up Current Before VCC Enable 18 25 µA VCC Regulator enable threshold 17 20 23 V VCC Regulator disable

7.25 V

threshold VIN ESD Clamp voltage I = 5mA 30 36 40 V

VIN

Operating supply current COMP = 0VDC 2.5 3.75 mA

VCC SUPPLY

Controller enable threshold 6.5 7 7.5 V Controller disable threshold 5.3 5.8 6.3 V VCC regulated output No External Load 8 8.5 9 V VCC dropout voltage (VIN -

I=5mA 1.7 V

VCC) VCC regulator current limit VCC = 7.5V (Note

15 22 mA

SKIP CYCLE MODE COMPARATOR

Skip Cycle mode enable

⁄3[COMP - 1.25V] 75 125 175 mV

threshold Skip Cycle mode hysteresis 5 mV

CURRENT LIMIT

CS limit to OUT delay CS stepped from 0

35 ns to 0.6V, time to OUT transition low, C

load

=0.

CS limit threshold 0.45 0.5 0.55 V Leading Edge Blanking time 90 ns CS blanking sinking impedance 35 55 Ω

SOFT-START

SS-OCV

SS pin open-circuit voltage 4.3 5.2 6.1 V Soft-start Current Source 15 22 30 µA Soft-start to COMP Offset 0.35 0.55 0.75 V COMP sinking impedance During SS ramp 60 Ω

OSCILLATOR

Frequency1 (RT = 44.2K) 135 150 165 kHz Frequency2 (RT = 13.3K) 440 500 560 kHz Sync threshold 2.4 3.2 3.8 V

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Electrical Characteristics Specifications in standard type face are for T

apply over the full Operating Junction Temperature Range. Unless otherwise specified: V

LM5021

3) (Continued)

= +25˚C and those in boldface type

= 15V, RT= 44.2KΩ. (Note

Symbol Parameter Conditions Min Typ Max Unit

PWM COMPARATOR

COMP to OUT delay COMP set to 2V

20 ns

CS stepped 0 to

0.4V, time to OUT transition low, C

load

=0. Min Duty Cycle COMP = 0V 0 % Max Duty Cycle (-1 Device) 75 80 85 % Max Duty Cycle (-2 Device) 50 % COMP to PWM comparator gain 0.33 COMP Open Circuit Voltage 4.2 5.1 6 V COMP at Max Duty Cycle 2.75 V COMP Short Circuit Current COMP = 0V 0.6 1.1 1.5 mA

SLOPE COMPENSATION

Slope Comp Amplitude (LM5021-1 only)

CS pin to PWM

Comparator offset at

70 90 110 mV

maximum duty cycle

OUTPUT SECTION

OUT High Saturation IOUT = 50mA, VCC

0.6 1.1 V

- OUT OUT Low Saturation IOUT = 100mA 0.3 1 V Peak Source Current OUT = VCC/2. 0.3 A Peak Sink Current OUT = VCC/2. 0.7 A Rise time C Fall time C

= 1nF 25 ns

load

= 1nF 10 ns

load

HICCUP MODE

V I I

OVLD

RST

DTCS

OVCS

Over load detection threshold COMP pin V Hiccup mode threshold SS pin V

HIC

SS-OCV

– 0.8 V – 0.8 V

SS-OCV

– 0.6 V – 0.6 V

SS-OCV

Hiccup mode Restart threshold SS pin 0.1 0.3 0.5 V Dead-time current source 0.1 0.25 0.4 µA Overload detection timer current

6 10 14 µA

– 0.4 V – 0.4 V

source

THERMAL RESISTANCE

Note 1: Absolute Maximum Ratingsare limitsbeyond which damageto thedevice may occur. Operating Ratingsare conditions underwhich operationof the device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.

Note 2: The human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin. Note 3: Min and Max limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical

Quality Control (SQC) methods. Limits are used to calculate National’s Average Outgoing Quality Level (AOQL).

Note 4: Device thermal limitations may limit usable range. Note 5: After initial turn-on at VIN = 20V.

MSOP-8 Junction to Ambient 0 LFM 200 ˚C/W

MDIP-8 Junction to Ambient 0 LFM 107 ˚C/W

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Simplified Block Diagram

LM5021

FIGURE 1.

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