SNVSAK0A October 2017 – October 2019 LM76002 , LM76003
PRODUCTION DATA.
The voltage regulation loop in the LM76002/LM76003 regulates the FB voltage to be the same as the internal reference voltage. The output voltage of the LM76002/LM76003 is set by a resistor divider to program the ratio from V_{OUT} to V_{FB}. The resistor divider is connected from the output node to ground with the mid-point connecting to the FB pin.
The voltage reference system produces a precise ±1% voltage reference over temperature. TI recommends using divider resistors with 1% tolerance or better with temperature coefficient of 100 ppm or lower. Selection of R_{FBT} equal or lower than 100 kΩ is also recommended. R_{FBB} can be calculated by Equation 1:
Larger R_{FBT} and R_{FBB} values reduce the current that goes through the divider, thus helping to increase light load efficiency. However, larger values also make the feedback path more susceptible to noise. If efficiency at very light load is not critical in a certain application, TI recommends R_{FBT} = 10 kΩ to 100 kΩ. If the resistor divider is not connected properly, output voltage cannot be regulated because the feedback loop is broken. If the FB pin is shorted to ground or disconnected, the output voltage is driven close to V_{IN} because the regulator detects very low voltage on the FB node. The load connected to V_{OUT} could be damaged in this case. It is important to route the feedback trace away from the noisy area of the PCB. For more layout recommendations, see Layout.
The minimum output voltage achievable equals VFB, with R_{FBB} open. The maximum V_{OUT} is limited by the maximum duty cycle at a given frequency:
where
Ideally, without frequency foldback, V_{OUT_MAX} = V_{IN_MIN} × D_{MAX}
Maximum output voltage with frequency foldback can be estimated using Equation 3: