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3.6 INTEGRATED DROOP FUNCTION (Optional)

Droop function realizes dependence between the regulated voltage and the delivered current (Load Reg-

ulation). In this way, a part of the drop due to the output capacitor ESR in the load transient is recovered.

As shown in Figure 12, the ESR drop is present in any case, but using the droop function the total devia-

tion of the output voltage is minimized.

Amplifier gain, the Output Characteristic is then given by the following relationship (when droop enabled):

with a remote amplifier gain of 1/2, the regulated output voltage results in being doubled.

The Droop current is equal to 50

µA at nominal full load and 70µA at the OC intervention threshold, so the

maximum output voltage deviation is equal to:

is sunk from the FB pin. The device regulates at the voltage programmed by the VID.

If this effect is not desired, shorting DROOP pin to SGND, the device regulates as a Voltage Mode Buck

converter.

Figure 12. Load Transient response (Left) and DROOP pin connection (Right).

3.7 MONITOR AND PROTECTIONS

The device monitors through pin VSEN the regulated voltage in order to build the PGOOD signal and man-

age the OVP / UVP conditions.

the programmed value (RA_Gain=1). It is an open drain output and it is enabled only after the soft start

is finished (2048 clock cycles after start-up). During Soft-Start this pin is forced low.

than one clock period, the device turns off all mosfets and resets restarting operations with a new soft-

start phase (hiccup mode, see Figure 13).

115% (min) of the programmed voltage (or the external reference) the controller permanently switches

on both the low-side mosfets and switches off both the high-side mosfets in order to protect the load.

The OSC/ FAULT pin is driven high (5V) and power supply (VCC) turn off and on is required to restart

operations.

Both Over Voltage and Under Voltage are active also during soft start (Under Voltage after than the

V

OUT

1

RA_Gain

-------------------------

VID

R

FB

I

DROOP

⋅

–

()

⋅

1

RA_Gain

-------------------------

VID

R

FB

R

SENSE

Rg

---------------------- I

OUT

⋅⋅

–

⎝⎠

⎛⎞

⋅

==

∆V

FULL

POSITIVE

–

LOAD

–

1

RA_Gain

------------------------- R

⋅

FB

50

µA

∆V

OC

INTERVENTION

–

1

RA_Gain

------------------------- R

⋅

FB

70

µA

⋅

–

=

⋅

–

=

V

MAX

V

MIN

V

NOM

ESR DROP

DROOP PIN = GND

DROOP PIN = FB PIN

Reference

I

DROOP

REMOTE

AMPLIFIER

ERROR

AMPLIFIER

DROOP

FB

COMP

VSEN

FBG

FBR

Remote

Ground

Remote

V

OUT

R

F

C

F

R

FB

R2

R2

R1

R1

Short to GND if DROOP function is not

implemented (Classic Voltage Mode).