LM5027ASQSLASHNOPB datasheet(22/35 Pages) TI

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VPWR - 2.0 - 20 PA x R1

2.0 x R1

R2 =

LM5027A

VIN

VCC

VPWR

10V

10V-15V (from

power stage)

LM5027A

SNVS642B – APRIL 2010 – REVISED MARCH 2013

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For Applications > 100V

For applications where the system input voltage (VPWR) exceeds 100V, VIN can be powered from an external

start-up regulator as shown in Figure 28. Connecting the VIN and VCC pins together allows the LM5027A to be

operated with VIN below 13V. To turn-off the internal start-up regulator the VCC voltage must be raised above

9.9V. The voltage at the VCC pin must not exceed 15V. The voltage source at the right side of Figure 28 is

typically derived from the power stage, and becomes active when the LM5027A outputs are active.

Figure 28. Start-up Regulator for VPWR > 100V

UVLO

The under-voltage lockout threshold (UVLO) is internally set to 2.0V at the UVLO pin. With two external resistors

as shown in Figure 29, the LM5027A is enabled when VPWR causes the UVLO pin to exceed threshold voltage of

2V. When VPWR is below the threshold, the internal 20 µA current sink is enabled to reduce the voltage at the

UVLO pin. When the UVLO pin voltage exceeds the 2V threshold, the 20 µA current sink is turned off causing

the UVLO voltage to increase and providing hysteresis. The values of R1 and R2 can be determined from the

following equation:

R1 = VHYS/20 µA

(5)

(6)

Where VHYS is the desired UVLO hysteresis at VPWR, and VPWR in the second equation is the turn-on voltage. For

example, if the LM5027A is to be enabled when VPWR reaches 34V, and the hysteresis is 1.8V, then R1 is 90 kΩ

and 5.6 k

Ω. For this application R1 was selected to be 90.0 kΩ, R2 was selected to be 6.19 kΩ. The LM5027A

can be remotely shutdown by taking the UVLO pin below 0.4V with an external open collector or open drain

device, as shown in Figure 29. The outputs and the VCC regulator are disabled in shutdown mode.

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LM5027ASQ/NOPB Datasheet(PDF) 22 Page - Texas Instruments