6.5

Duty cycle range

Minimum ON-time (tON_MIN) is the shortest duration of time that the high-side switch can be turned on. tON_MIN is

typically 100 ns.

Minimum OFF-time (tOFF_MIN) is the shortest duration of time that the high-side switch can be off. tOFF_MIN is

typically 120 ns. In CCM operation, tON_MIN and tOFF_MIN limit the voltage conversion range without switching

frequency foldback.

The minimum duty cycle without frequency foldback allowed is:

DMIN=tON_min∙FSW

(5)

The maximum duty cycle without frequency foldback allowed is:

DMAX=1− tOFF_min∙FSW

(6)

Given a required output voltage, the maximum VIN can be found by:

VIN_MAX=VOUT/tON_min∙FSW

(7)

6.6

Overcurrent protection

The current protection circuitry features a constant current protection, so the device limits the maximum peak

current (please refer to Table 7) in overcurrent condition.

The DCP3601 device implements a pulse-by-pulse current sensing on both power elements (high-side and low-

side switches) for effective current protection over the duty cycle range. The high-side current sensing is called

“peak”, the low-side sensing “valley”.

The internal noise generated during the switching activity makes the current sensing circuitry ineffective for a

minimum conduction time of the power element. This time is called “masking time” because the information from

the analog circuitry is masked by the logic to prevent an erroneous detection of the overcurrent event. Therefore,

the peak current protection is disabled for a masking time after the high-side switch is turned on. The masking

time for the valley sensing is activated after the low-side switch is turned on. In other words, the peak current

protection can be ineffective at extremely low duty cycles, the valley current protection at extremely high duty

cycles.

The DCP3601 device assures an effective overcurrent protection sensing the current flowing in both power

elements. In case one of the two current sensing circuitry is ineffective because of the masking time, the device is

protected sensing the current on the opposite switch. Thus, the combination of the “peak” and “valley” current

limits assure the effectiveness of the overcurrent protection even in extreme duty cycle conditions.

In case the current diverges because of the high-side masking time, the low-side power element is turned on until

the switch current level drops below the valley current sense threshold. The low-side operation is able to prevent

the high-side turn-on, so the device can skip pulses decreasing the switching frequency.

DCP3601

Functional description

DS14782 - Rev 1

page 9/26