Datasheet

VIN
FBCOMP
VCC
OUT
RT
UVLO GND
CS
SS
LM5022
L1
D1
Q1
C1
C2R1
C
F
C
SS
C
O1,2
C
IN1,2
R
T
R
UV1
R
UV2
R
FB1
R
FB2
R
SNS
V
IN
= 9V to 16V
V
O
= 40V
C
CS
R
S1
C
INX
R
S2
C
OX
LM5022
www.ti.com SNVS480G –JANUARY 2007–REVISED DECEMBER 2013
Example Circuit
Figure 12. Design Example Schematic
APPLICATIONS INFORMATION
OVERVIEW
The LM5022 is a low-side N-channel MOSFET controller that contains all of the features needed to implement
single ended power converter topologies. The LM5022 includes a high-voltage startup regulator that operates
over a wide input range of 6V to 60V. The PWM controller is designed for high speed capability including an
oscillator frequency range up to 2 MHz and total propagation delays less than 100 ns. Additional features include
an error amplifier, precision reference, input under-voltage lockout, cycle-by-cycle current limit, slope
compensation, soft-start, oscillator sync capability and thermal shutdown.
The LM5022 is designed for current-mode control power converters that require a single drive output, such as
boost and SEPIC topologies. The LM5022 provides all of the advantages of current-mode control including input
voltage feed-forward, cycle-by-cycle current limiting and simplified loop compensation.
HIGH VOLTAGE START-UP REGULATOR
The LM5022 contains an internal high-voltage startup regulator that allows the VIN pin to be connected directly to
line voltages as high as 60V. The regulator output is internally current limited to 35 mA (typical). When power is
applied, the regulator is enabled and sources current into an external capacitor, C
F
, connected to the VCC pin.
The recommended capacitance range for C
F
is 0.1 µF to 100 µF. When the voltage on the VCC pin reaches the
rising threshold of 5V, the controller output is enabled. The controller will remain enabled until VCC falls below
4.7V. In applications using a transformer, an auxiliary winding can be connected through a diode to the VCC pin.
This winding should raise the VCC pin voltage to above 7.5V to shut off the internal startup regulator. Powering
VCC from an auxiliary winding improves conversion efficiency while reducing the power dissipated in the
controller. The capacitance of C
F
must be high enough that it maintains the VCC voltage greater than the VCC
UVLO falling threshold (4.7V) during the initial start-up. During a fault condition when the converter auxiliary
winding is inactive, external current draw on the VCC line should be limited such that the power dissipated in the
start-up regulator does not exceed the maximum power dissipation capability of the controller.
An external start-up or other bias rail can be used instead of the internal start-up regulator by connecting the
VCC and the VIN pins together and feeding the external bias voltage (7.5V to 14V) to the two pins.
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