LM5033SD-EVAL National Semiconductor, LM5033SD-EVAL Datasheet - Page 9

• Manufacturer Part Number: LM5033SD-EVAL
• Description: BOARD EVALUATION LM5033SD
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5033SD-EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 9V
• Current - Output: 20A
• Voltage - Input: 40 ~ 60V
• Regulator Topology: Buck
• Frequency - Switching: 315kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM5033
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -
• Lead Free Status / Rohs Status: Not Compliant

Current Sense (Pin 8)
The external current sensing circuit should include an RC
filter located near the IC to prevent false triggering of the
Current Sense comparator due to transients or noise. An
internal MOSFET discharges the external filter capacitor at
the conclusion of each PWM cycle to improve dynamic
performance. The discharge time is equal to the deadtime
between Out1 and Out2 at maximum duty cycle. Additionally,
pin 8 is pulled low when V
threshold or when an over temperature condition occurs.
Oscillator, Sync Capability (Pin 9)
The LM5033 oscillator frequency is set by a single external
resistor connected between Rt/Sync and ground. The re-
quired Rt resistor is calculated from:
The outputs (Out1 and Out2) alternate at half the oscillator
frequency. The voltage at the Rt/Sync pin is internally regu-
lated to a nominal 2.0V. The Rt resistor should be located as
close as possible to the IC, and connected directly to the
pins (Rt and GND).
The LM5033 can be synchronized to an external clock by
applying a narrow pulse to pin 9. The external clock must be
a higher frequency than the free running frequency set by
the Rt resistor, and the pulse width must be between 15 and
150 ns. The clock signal must be coupled into the Rt/Sync
pin through a 100 pF capacitor. When the synchronizing
pulse transitions low-to-high, the voltage at pin 9 must ex-
ceed 3.8V from its nominal 2.0V dc level. During the clock
signal’s low time the voltage at pin 9 will be clamped at 2.0V
by an internal regulator. The Rt resistor is always required,
whether the oscillator is free running or externally synchro-
nized.
Soft Start (Pin 10)
The softstart feature allows the converter to gradually reach
a steady state operating point, thereby reducing start-up
stresses and current surges. Upon turn-on, after the under-
voltage sensor resets at V
source charges an external capacitor at pin 10 to generate a
ramping voltage (0 to + 5V) which allows the voltage on the
Comp pin (pin 3) to increase gradually. As the COMP voltage
increases the output duty cycle will increase from zero to the
value required for regulation. Internally, the softstart pin is
pulled low when a current fault is detected at pin 8, the V
voltage is below the lower threshold of the under-voltage
sensor, or when a thermal shutdown occurs. Additionally, the
softstart pin can be pulled low by an external device.
In the event of a current fault, (see Current Sense section)
the softstart capacitor will be discharged by an internal pull-
down device. The falling voltage at pin 10 will pull down the
COMP pin, thereby ensuring a minimum output duty cycle
when the outputs are re-enabled. The softstart capacitor will
then begin to ramp up, allowing the COMP voltage to in-
crease. As the COMP voltage increases, the output duty
cycle increases from zero to the value required for regula-
tion. However, if the fault condition is still present the above
sequence repeats until the fault is removed.
If the V
threshold (typically 6.8V) the outputs are disabled, and the
CC
voltage falls below the lower under-voltage sensor
CC
CC
, an internal 10 µA current
is below the under-voltage
(Continued)
CC
9
softstart capacitor is discharged. The falling voltage at pin 10
will pull down the COMP pin, thereby ensuring minimum
output duty cycle when the outputs are re-enabled. After the
V
9.5V), the outputs are enabled, and the softstart capacitor
will begin to ramp up, allowing the COMP pin voltage to
increase. The output duty cycle will then increase from zero
to the value required for regulation.
In the event of a fault which results in an excessively high die
temperature, an internal Thermal Shutdown circuit is pro-
vided to protect the IC. When activated (at 165˚C) the IC is
forced into a low power reset state, disabling the output
drivers and the V
reduced (typical hysteresis = 15˚C), the V
enabled and a softstart sequence will initiate.
Using an externally controlled switch, the outputs (Pins 5 &
6) can be disabled at any time by pulling pin 10 below 0.5V.
This will pull down the COMP pin to near ground, causing the
output duty cycle to go to zero. Upon releasing pin 10, the
softstart capacitor will ramp up, allowing the COMP pin
voltage to increase. The output duty cycle then increases
from zero to the value required for regulation.
OUT1, OUT2 (Pins 5, 6)
The LM5033 provides two alternating outputs, OUT1 and
OUT2, each capable of sourcing and sinking 1.5A peak.
Each will toggle at one-half the internal oscillator frequency.
The voltage output levels are nominally ground and V
minus a saturation voltage at each level which depends on
the current flow.
The outputs can drive power MOSFETs directly in a push-
pull application, or they can drive a high voltage gate driver
(e.g., LM5100) in a bridge application.
The outputs are disabled when any of the following condi-
tions occur:
1. An overcurrent condition is detected at pin 8,
2. The V
3. An over-temperature condition is detected, or
4. The voltage at Pin 10 is below 0.5V
Thermal Protection
The system design should limit the LM5033 junction tem-
perature to not exceed 125˚C during normal operation. How-
ever, in the event of a fault which results in a higher die
temperature, an internal Thermal Shutdown circuit is pro-
vided to protect the IC. When thermal shutdown is activated,
typically at 165˚C, the IC is forced into a low power reset
state disabling the output drivers and the V
feature helps prevent catastrophic failures from accidental
device overheating. When the die temperature has reduced
(typical hysteresis = 15˚C) the V
a softstart sequence initiates.
Application Information
The following information is intended to provide guidelines
for implementing the LM5033. However, final selection of all
external components is dependent on the configuration and
operating characteristics of the complete power conversion
system.
CC
voltage increases above the upper threshold (typically
CC
under-voltage sensor is active,
CC
regulator. When the die temperature has
CC
regulator is enabled and
CC
CC
regulator. This
regulator is
www.national.com
CC
,