LM5020

C5

0.01 PF

SS

R6

12.4k

GND

GND

C8

100 pF

RT/

SYNC

10

9

3

U1

GND

6

FB

2

CS

8

100

R7

C11

1000 pF

R8

0.47

R9

0.47

GND

GND

GND

OUT

5

UVLO

7

VIN

1

VCC

4

C10

4.7 PF

C4

0.1 PF

GND

GND

R1

10

R4

1.00k

R2

61.9k

C2

2.2 PF

GND

C1

2.2 PF

GND

Shutdown

C3

0.01 PF

GND

R3

2.87k

GND

V+

1

J1

30-75V IN

Q1

Si7898DP

GND

D1

CMPD2838E

Z1

1SMB5936B

GND

T1

D3

MBRD835L

D2

CMPD2838E

20

R13

GND

C12

470 pF

10, 1W

R10

GND

R12

1.47k

R11

2.43k

0.1 PF

C9

GND

OUT RTN

1

2

GND

GND

2

J2

+3.3V

C13

100 PF

GND

C14

100 PF

GND

C15

270 PF

GND

COMP

SYNC

Input

R5

15.0k

C7

3300 pF

C6

220 pF

LM5020

www.ti.com

SNVS275F – MAY 2004 – REVISED APRIL 2006

Soft Start

The softstart feature allows the power converter to gradually reach the initial steady state operating point, thereby

thresholds are satisfied, an internal 10µA current source charges an external capacitor connected to the SS pin.

The capacitor voltage will ramp up slowly and will limit the COMP pin voltage and the duty cycle of the output

pulses.

Gate Driver and Maximum Duty Cycle Limit

The LM5020 provides an internal gate driver (OUT), which can source and sink a peak current of 1 Amp. The

LM5020 is available in two duty cycle limit options. The maximum output duty cycle is typically 80% for the

LM5020-1 option and precisely equal to 50% for the LM5020-2 option. The maximum duty cycle function for the

LM5020-2 is accomplished with an internal toggle flip-flop which ensures an accurate duty cycle limit. The

internal oscillator frequency of the LM5020-2 is therefore twice the operating frequency of the PWM controller

(OUT pin).

The 80% maximum duty cycle limit of the LM5020-1 is determined by the internal oscillator and varies more than

the 50% limit of the LM5020-2. For the LM5020-1 the internal oscillator frequency and the operational frequency

of the PWM controller are equal.

Thermal Protection

Internal thermal shutdown circuitry is provided to protect the integrated circuit in the event the maximum junction

temperature is exceeded. This feature prevents catastrophic failures from accidental device overheating. When

activated, typically at 165 degrees Celsius, the controller is forced into a low power standby state, disabling the

regulator is enabled and a softstart sequence initiated.

Copyright © 2004–2006, Texas Instruments Incorporated

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