What must be taken into account if CE pin is tied to VDD pin? Is it necessary to pull up CE pin to VDD pin by a resistor?

LDO Linear RegulatorsVoltage Detectors (Reset ICs)DC/DC Switching RegulatorsHow to use

Basically, CE pin and VDD pin can be directly tied, and there is no need to insert a resistor between the VDD pin and CE pin when making the LDO constantly ON without controlling CE pin.

But, if start-up of the power input is slow, LDO may active before the input voltage reaches the set output voltage. In that case, if the line transient response characteristic is poor, the output voltage may be unstable. Also if the power supply input may rapidly changed by a cause such as the power flicker, the output may also become unstable. In order to prevent these problems, we recommend that the level of CE pin shifted according to the set output voltage. Please refer to the circuit example 1. 

Some of our products have a CE pin with a diode connected to the VIN pin as an electrostatic discharge (ESD) protection element. If the CE pin voltage of these products exceeds the VIN + Vf of the internal ESD protection diode voltage, the IC might be damaged seriously by a large current flowing from the CE pin. In this case, we recommend that a resistor be inserted to reduce the amount of the current flowing from the CE. Please refer to the circuit example 2.

• Circuit example 1

  VDD is divided by resistors and if necessary, add a capacitor between CE and GND to make some delay for rising CE pin's level.

  

• Circuit example 2