CMPWR150 datasheet(8/15 Pages) ONSEMI

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CMPWR150

Rev. 3 | Page 8 of 15 | www.onsemi.com

Typical Transient Characteristics

The transient characterization test set-up shown below includes the effective source impedance of the V

supply (R

S). This was measured to be approximately 0.2Ω. It is recommended that this effective source

impedance be no greater than 0.25

Ω to ensure precise switching is maintained during V

CC selection and

deselection.

Both the rise and fall times during V

CC power-up/down sequencing were controlled at a 20 millisecond duration.

This is considered to represent worst case conditions for most application circuits.

A maximum rated load current of 500mA was used during characterization, unless specified otherwise.

During a selection or deselection transition, the DC load current is switching from V

AUX to VCC and vice versa. In

addition to the normal load current, there may also be an in-rush current for charging/discharging the load

capacitor. The total current pulse being applied to either V

AUX or VCC is equal to the sum of the DC load and the

corresponding in-rush current. Transient currents in excess of 1.0 amps can readily occur for brief intervals

when either supply commences to power the load.

The oscilloscope traces of V

CC power-up/down show the full bandwidth response at the VCC

and V

OUT pins under

full load (500mA) conditions.

See Application Note AP-211 for more information.

CC Power-up Cold Start.

Figure 5 shows the output response during an initial V

CC power-up with VAUX not

present. When V

CC reaches the select threshold, the regulator turns on.

The uncharged output capacitor

causes maximum in-rush current to flow, resulting in a large voltage disturbance at the V

CC pin of about 230mV.

The built-in hysteresis of 250mV ensures the regulator remains enabled throughout the transient.

Prior to V

CC reaching an acceptable logic supply level (2V), a disturbance on the Drive pin can be observed.

PowerUpCold.bmp

Figure 5. V

CC Power-up Cold Start

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