Datasheet

VCC1
VCC2
8V - 15V
LM5034
C2
C1
VIN
8V-15V
Start-up
Voltage
V
PWR
VIN
VCC1
VCC2
8V - 15V (from
power stage)
C2
C1
LM5034
9V
0.1
0.1 PF
50
LM503
4
V
IN
V
PWR
LM5034
www.ti.com SNVS347A –FEBRUARY 2005–REVISED APRIL 2013
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 loads on the
VCC pins. If the power dissipation associated with the VIN current exceeds the package capability, an external
voltage should be applied to the VCC pins (see Figure 6 & Figure 7) to reduce power in the internal start-up
regulator. It is recommended the circuit of Figure 26 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 LM5034.
When all internal bias currents for the LM5034 and output driver currents are supplied through VIN and the
internal V
CC
regulator, the required input current (I
IN
) is shown in Figure 6 & Figure 7. In most applications, upon
turn-on, I
IN
increases with V
IN
as shown in Figure 6 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 26. Input Transient Production
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 27, or from any other low voltage source as shown in Figure 28.
Connecting VIN and the VCC together allows the LM5034 to be operated with VIN below 13V. The voltage at the
VCC pins must not exceed 15V. The voltage source at the right side of Figure 27 is typically derived from the
power stage, and becomes active once the LM5034’s outputs are active.
Figure 27. Start-up Regulator for V
PWR
>100V
Figure 28. Bypassing the Internal Start-up Regulator
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