Datasheet

0.1 PF
50
LM5032
VIN
V
PWR
PWM
OUT
GND
LM5032
VCC
LM5032
SNVS344A –MARCH 2005–REVISED APRIL 2013 www.ti.com
OUT1 and OUT2 are compound gate drivers with CMOS and Bipolar output transistors as shown in Figure 21.
The parallel MOS and Bipolar devices provide a faster turn-off of the primary switch thereby reducing switching
losses. The outputs switch at one-half the oscillator frequency with the rising edges at OUT1 and OUT2 180° out
of phase with each other. The on-time of OUT1 and OUT2 is determined by their respective duty cycle control.
Figure 21. Compound Gate Driver
Thermal Shutdown
The LM5032 should be operated so the junction temperature does not exceed 125°C. If a junction temperature
transient reaches 165°C (typical), the Thermal Shutdown circuit activates the V
CC
Disable and Drivers Off lines
(see Figure 17). The V
CC
regulator and the four output drivers are disabled, the SS1, SS2, and RES pins are
grounded, and the soft-start current is set to 50 µA. This puts the LM5032 in a low power state helping to prevent
catastrophic failures from accidental device overheating. When the junction temperature reduces below 145°C
(typical hysteresis = 20°C), the V
CC
regulator is enabled and a startup sequence is initiated (Figure 4).
APPLICATIONS INFORMATION
VIN
The voltage applied to the VIN pin, normally the same as the system voltage applied to the power transformer’s
primary (V
PWR
), can vary in the range of 13 to 100V with transient capability to 105V. The current into VIN
depends primarily on the output driver capacitive loads, the switching frequency, and any external load at VCC. If
the power dissipation associated with the VIN current exceeds the package capability, an external voltage should
be applied to VCC (see Figure 5 & Figure 6) to reduce power in the internal start-up regulator. It is recommended
the circuit of Figure 22 be used to suppress transients which may occur at the input supply, in particular where
VIN is operated close to the maximum operating rating of the LM5032.
When all internal bias currents for the LM5032 and output driver currents are supplied through VIN and the
internal V
CC
regulator, the required input current (I
IN
) is shown in Figure 5 & Figure 6. In most applications, upon
turn-on, I
IN
increases with V
IN
as shown in Figure 5 until the UVLO threshold is reached. After the outputs are
enabled and the external VCC supply voltage is active, the current into VIN then drops to a nominal 120 µA.
Figure 22. Input Transient Protection
FOR APPLICATIONS >100V
For applications where the system input voltage (V
PWR
) exceeds 100V, VIN can be powered from an external
start-up regulator as shown in Figure 23, or from any other low voltage source as shown in Figure 24.
Connecting VIN and VCC together allows the LM5032 to be operated with VIN below 13V. The voltage at VCC
must not exceed 15V. The voltage source at the right side of Figure 23 is typically derived from the power stage,
and becomes active once the LM5032’s outputs are active.
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