7.3.4 Startup and Noise Reduction Capacitor

Fixed voltage versions of the TPS735-Q1 family of devices use a quick-start circuit to fast-charge the noise reduction capacitor, C_NR, if present (see the Functional Block Diagram section). This architecture allows the combination of very-low output noise and fast startup times. The NR pin is high impedance so a low-leakage C_NR capacitor must be used. Most ceramic capacitors are appropriate in this configuration. A high-quality, COG-type (NPO) dielectric ceramic capacitor is recommended for C_NR when used in environments where abrupt changes in temperature can occur.

Note that for fastest start-up, apply V_IN first, then drive the enable pin (EN) high. If the EN pin is tied to the IN pin, start-up is somewhat slower. Refer to the Typical Application section (see Figure 17 and Figure 18). The quick-start switch is closed for approximately 135 μs. To ensure that C_NR is charged during the quick-start time, use a capacitor with a value of no more than 0.01 μF.