LM5022LEDEVAL National Semiconductor, LM5022LEDEVAL Datasheet - Page 8

• Manufacturer Part Number: LM5022LEDEVAL
• Description: BOARD EVALUATION FOR LM5022
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5022LEDEVAL

• Current - Output / Channel: 1A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 40V
• Features: Dimmable
• Voltage - Input: 10 ~ 14V
• Utilized Ic / Part: LM5022
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Example Circuit
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. Addi-
tional features include an error amplifier, precision reference,
input under-voltage lockout, cycle-by-cycle current limit, slope
compensation, soft-start, oscillator sync capability and ther-
mal shutdown.
The LM5022 is designed for current-mode control power con-
verters that require a single drive output, such as boost and
SEPIC topologies. The LM5022 provides all of the advan-
tages 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 regu-
lator 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 ca-
pacitor, C
capacitance range for C
age on the VCC pin reaches the rising threshold of 5V, the
controller output is enabled. The controller will remain en-
abled 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 reg-
ulator. Powering VCC from an auxiliary winding improves
conversion efficiency while reducing the power dissipated in
the controller. The capacitance of C
F
, connected to the VCC pin. The recommended
F
is 0.1 µF to 100 µF. When the volt-
F
must be high enough
FIGURE 1. Design Example Schematic
8
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, ex-
ternal 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 con-
troller.
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.
INPUT UNDER-VOLTAGE DETECTOR
The LM5022 contains an input Under Voltage Lock Out (UV-
LO) circuit. UVLO is programmed by connecting the UVLO
pin to the center point of an external voltage divider from VIN
to GND. The resistor divider must be designed such that the
voltage at the UVLO pin is greater than 1.25V when VIN is in
the desired operating range. If the under voltage threshold is
not met, all functions of the controller are disabled and the
controller remains in a low power standby state. UVLO hys-
teresis is accomplished with an internal 20 µA current source
that is switched on or off into the impedance of the set-point
divider. When the UVLO threshold is exceeded, the current
source is activated to instantly raise the voltage at the UVLO
pin. When the UVLO pin voltage falls below the 1.25V thresh-
old the current source is turned off, causing the voltage at the
UVLO pin to fall. The UVLO pin can also be used to implement
a remote enable / disable function. If an external transistor
pulls the UVLO pin below the 1.25V threshold, the converter
will be disabled. This external shutdown method is shown in
Figure
2.
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