SNVS288K September 2004 – September 2018 LM2734
An alternative method when VIN is greater than 5.5 V is to place the zener diode D3 in a shunt configuration. A small 350 mW to 500 mW 5.1 V zener in a SOT or SOD package can be used for this purpose. A small ceramic capacitor such as a 6.3 V, 0.1 μF capacitor (C4) should be placed in parallel with the zener diode. When the internal NMOS switch turns on, a pulse of current is drawn to charge the internal NMOS gate capacitance. The 0.1 μF parallel shunt capacitor ensures that the VBOOST voltage is maintained during this time.