Datasheet

LM2677
www.ti.com SNVS077I –MAY 2004–REVISED JUNE 2012
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This is the input to a two-stage high gain amplifier, which drives the PWM controller. It is necessary to connect
pin 6 to the actual output of the power supply to set the dc output voltage. For the fixed output devices (3.3V, 5V
and 12V outputs), a direct wire connection to the output is all that is required as internal gain setting resistors are
provided inside the LM2677. For the adjustable output version two external resistors are required to set the dc
output voltage. For stable operation of the power supply it is important to prevent coupling of any inductor flux to
the feedback input.
ON/OFF
This input provides an electrical ON/OFF control of the power supply. Connecting this pin to ground or to any
voltage less than 0.8V will completely turn OFF the regulator. The current drain from the input supply when OFF
is only 50μA. Pin 7 has an internal pull-up current source of approximately 20μA and a protection clamp zener
diode of 7V to ground. When electrically driving the ON/OFF pin the high voltage level for the ON condition
should not exceed the 6V absolute maximum limit. When ON/OFF control is not required pin 7 should be left
open circuited.
DAP (VSON PACKAGE)
The Die Attach Pad (DAP) can and should be connected to PCB Ground plane/island. For CAD and assembly
guidelines refer to Application Note AN-1187 (SNOA401).
DESIGN CONSIDERATIONS
Figure 19. Basic circuit for fixed output voltage applications.
Figure 20. Basic circuit for adjustable output voltage applications
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