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is used for a VRM module. The very low offset amplifier senses the output voltage remotely through the

pins FBR and FBG (FBR is for the regulated voltage sense while FBG is for the ground sense) and reports

this voltage internally at VSEN pin with unity gain eliminating the errors. Keeping the FBR and FBG traces

parallel and guarded by a power plane results in common mode coupling for any picked-up noise.

comes not connected and still senses the output voltage through the remote buffer. In this case the FBG

and FBR pins must be connected anyway to the regulated voltage (See figure 9).

The remote buffer is included in the trimming chain in order to achieve ±0.5% accuracy on the output volt-

age when the RB Is used: eliminating it from the control loop causes the regulation error to be increased

by the RB offset worsening the device performances.

Figure 8. Remote Buffer Connections

OUTPUT VOLTAGE MONITOR PROTECTION

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

age the OVP / UVP conditions comparing this voltage level with the programmed reference VID*.

Power good output is forced low if the voltage sensed by VSEN is not within ±12% (Typ.) of the pro-

grammed value. 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.

Under voltage protection is provided. If the output voltage monitored by VSEN drops below the 60% of the

reference voltage for more than one clock period, the device turns off all mosfets and the OSC/FAULT is

driven high (5V). The condition is latched, to recover it is required to cycle the power supply.

Over Voltage protection is also provided:

Once VCC crosses the turn-ON threshold, when the voltage monitored by VSEN reaches 125% (Typ.) of

the programmed voltage the controller permanently switches on both the low-side mosfets and switches

off both the high-side mosfets in order to protect the CPU. 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 output

voltage reaches 0.6V). The reference used in this case to determine the UV thresholds is the increasing

voltage driven by the 2048 soft start digital counter while the reference used for the OV threshold is the

final reference programmed by the VID pins.

Reference

REMOTE

BUFFER

ERROR

AMPLIFIER

FB

COMP

VSEN

FBG

FBR

Remote

Ground

Remote

32k

32k

32k

32k

Reference

REMOTE

BUFFER

ERROR

AMPLIFIER

FB

COMP

VSEN

FBG

FBR

32k

32k

32k

32k

RB used (±0.5% Accuracy)

RB Not Used