Datasheet

LM5033
SNVS181B –APRIL 2004–REVISED APRIL 2013 www.ti.com
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 increase. As the COMP voltage increases, the output duty cycle increases from zero to the
value required for regulation. However, if the fault condition is still present the above sequence repeats until the
fault is removed.
If the V
CC
voltage falls below the lower under-voltage sensor threshold (typically 6.8V) the outputs are disabled,
and the 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
CC
voltage increases above the
upper threshold (typically 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 provided 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
CC
regulator. When the die temperature has reduced (typical hysteresis = 15°C), the
V
CC
regulator is 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
CC
, 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 conditions occur:
1. An overcurrent condition is detected at pin 8,
2. The V
CC
under-voltage sensor is active,
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 temperature to not exceed 125°C during normal operation.
However, in the event of a fault which results in a higher die temperature, an internal Thermal Shutdown circuit is
provided 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
CC
regulator. This feature helps prevent catastrophic
failures from accidental device overheating. When the die temperature has reduced (typical hysteresis = 15°C)
the V
CC
regulator is enabled and 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.
V
IN
(PIN 1)
The voltage applied at pin 1, normally the same as that applied to the main transformer’s primary, can be in the
range of 15 to 90V, with transient capability to 100V. The current into pin 1 depends not only on V
IN
, but also on
the load on the output driver pins, any load on V
CC
, and whether or not an external voltage is applied to V
CC
. If
Vin is close to the absolute maximum rating of the LM5033, it is recommended the circuit of Figure 13 be used to
filter transients which may occur at the input supply.
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