Datasheet
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
GNDGND
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
3
2
1
4
Q1
Si7898DP
6
7
8
5
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
reducing start-up stresses and current surges. At power on, after the V
CC
and the line undervoltage lockout
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
output driver and the bias regulator. After the temperature is reduced (typical hysteresis = 25°C) the V
CC
regulator is enabled and a softstart sequence initiated.
Typical Application Circuit: 36V - 75 V
IN
and 3.3V, 4.5A OUT
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