I am using an LM3489 buck controller in a power supply. It has an enable/shutdown pin. When the EN pin is low, the device is deactivated. The datasheet describes a typical control scheme using an open collector transistor. That could be easily done with a PIC pin driving a small transistor.
The following statement from the LM3489 datasheet caught my attention:
I am using a PIC12F509 to control the enable pin with GP2 (pin5) and had intended to use a direct connection or resistor, say 1K, to prevent excessive current. (Total supply current in shutdown is 7 uA, so I assume the most the EN pin can source is = < 7uA.)
Microchip, however, gives the following warning:
1) Is that assumption correct?
2) Should I still use a resistor?
3) Or, should I take the most conservative approach and use a transistor driven by the PIC?
Thanks in advance.
John
The following statement from the LM3489 datasheet caught my attention:
Elsewhere, it is stated that the EN pin is internally pulled high with the voltage clamped at 8V typical.For normal operation this pin should be left open. In case an external voltage control source is applied to this pin for enable control, the applied voltage should not exceed the maximum operating voltage level..., i.e., 5.5V
I am using a PIC12F509 to control the enable pin with GP2 (pin5) and had intended to use a direct connection or resistor, say 1K, to prevent excessive current. (Total supply current in shutdown is 7 uA, so I assume the most the EN pin can source is = < 7uA.)
Microchip, however, gives the following warning:
I am assuming that with the low currents involved, the PIC output pin will not be driven high or low. Therefore, I can use a direct connection.A pin actively outputting a high or low should not be driven from external devices at the same time in order to change the level on this pin. The resulting high output currents may damage the chip.
1) Is that assumption correct?
2) Should I still use a resistor?
3) Or, should I take the most conservative approach and use a transistor driven by the PIC?
Thanks in advance.
John