EN

LM5015

1.26V

6 PA

STANDBY

(DISABLE PWM

CONTROLLER)

R1

R2

0.45V

SHUTDOWN VCC LDO

VIN

6V

1k

R1 =

1.26V

R2 =

LM5015

SNVS538C – NOVEMBER 2007 – REVISED APRIL 2013

www.ti.com

EN / UVLO VOLTAGE DIVIDER SELECTION

Two dedicated comparators connected to the EN pin are used to implement input under-voltage lockout and a

shutdown condition. When the EN pin voltage is below 0.45V, the controller is in a low current shutdown mode

where the VIN current is reduced to 110 µA. For an EN pin voltage greater than 0.45V but less than 1.26V the

controller is in standby mode, with all internal circuits operational, but with the power MOSFETs disabled. Once

the EN pin voltage is greater than 1.26V, the controller is fully enabled and the HO and LO outputs commence

switching. Two external resistors can be used to program the minimum operational voltage for the power

converter as shown in Figure 18. When the EN pin voltage falls below the 1.26V threshold, an internal 100 mV

threshold hysteresis prevents noise from toggling the state. Therefore, the voltage at the EN pin must be reduced

to 1.16V to transition to the standby state. Resistance values for R1 and R2 can be determined from the

and R2.

(4)

would set R1 to 29.4 k

Ω and R2 to 2.49 kΩ. If the voltage at the EN pin can exceed 6V, then the current into the

6V protection Zener must be limited below 4 mA by the external resistors. Be sure to check both the power and

voltage rating for the selected R1 resistor (some 0603 resistors are rated as low as 50V maximum operating

voltage).

Figure 18. Basic EN (UVLO) Configuration

A remote enable function can be accomplished with open drain device(s) connected to the EN pin as shown in

Figure 19. A MOSFET or an NPN transistor connected to the EN pin will force the regulator into the low power

‘off’ state. Adding a PN diode in the drain (or collector) provides the offset to achieve the standby state. The

advantage of standby is that the VCC LDO is not disabled and external circuitry powered by VCC remains

functional.

16

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