6

Functional description

The DCP3601 device is based on a “peak current mode" architecture with constant frequency control. Therefore,

the intersection between the error amplifier output and the sensed inductor current generates the PWM control

signal to drive the power switch.

The device features LNM (low noise mode) that is forced PWM control, or LCM (low consumption mode) to

increase the efficiency at light-load on the selected part number.

The main internal blocks shown in the block diagram are:

•

Embedded power elements

•

A fully integrated saw tooth oscillator with the ramp for the slope compensation avoiding subharmonic

instability

•

The transconductance error amplifier with integrated compensation network

•

The high-side current sense amplifier to sense the inductor current

•

A “pulse width modulator” (PWM) comparator and the driving circuitry of the embedded power elements

•

The soft-start blocks to ramp the error amplifier reference voltage and so decrease the inrush current at

power-up. The EN pin inhibits the device when driven low

•

The EN pin switches the device on and off

•

The current limitation circuit to implement the constant current protection, sensing pulse-by-pulse the high-

side / low-side switch current

•

A circuit to implement the thermal protection function

•

Dithering

•

The OVP circuitry to discharge the output capacitor in case of overvoltage event

6.1

EN

The EN pin controls the ON/OFF operation of the buck converter. If the voltage is less than 0.95 V, it shuts down

the device, while a voltage of greater than 1.36 V is required to start the converter.

The EN pin is an input and cannot be left open or floating. The simplest way to enable the operation of the

DCP3601 is to connect the EN to VIN. This allows self-startup when VIN is within the operating range.

6.2

Soft-start

The soft-start (SS) limits the inrush current surge and makes the output voltage increase monotonically. The

device implements the soft-start phase ramping the internal reference with very small steps. Once the SS ends,

the error amplifier reference is switched to the internal value of 0.85 V coming directly from the bandgap cell.

During normal operation, a new soft-start cycle takes place in case of:

1. Thermal shutdown event

2. UVLO event

3. EN pin rising over VEN threshold

6.3

Light-load operation

The DCP3601 implements two different light-load strategies:

1. Low consumption mode (LCM)

2. Low noise mode (LNM)

Refer to Table 9 to select the part number with the preferred light-load strategy.

6.3.1

Low consumption mode (LCM)

Low consumption mode (LCM) is an advanced feature that enhances the efficiency under light-load conditions.

When the switch peak current request is lower than the ISKIP threshold (see Table 7), the device regulates VOUT

by the skip threshold, generating pulses at a variable frequency that is inversely proportional to the load. The duty

cycle of the pulses may remain relatively constant, but the interval between pulses increases as the load

decreases.

DCP3601

Functional description

DS14782 - Rev 1

page 7/26