L6706 datasheet(24/47 Pages) STMICROELECTRONICS

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Output current monitoring (IMON)

L6706

24/47

Doc ID 15698 Rev 2

Output current monitoring (IMON)

The device sources from IMON pin a current proportional to the load current (the sourced

current is a copy of droop current).

Connect IMON pin through a RIMON resistor to remote ground (GND Core) to implement a

load indicator, as shown in Figure 9.

As INTEL VR11.1 specification required, on the IMON voltage as to be added a small

positive offset to avoid under-estimation of the output load (due to elements accuracy).

The voltage across IMON pin is given by the following formula:

where:

The IMON pin voltage is clamped to 1.100 V max to preserve the CPU from excessive

voltages as INTEL VR11.1 specification required.

Figure 9.

Output monitoring connection (left) and thermal compensation (right)

Current sense element (DCR inductor) has a non-negligible temperature variation. As a

consequence, the sensed current is subjected to a measurement error that causes the

monitoring voltage to vary accordingly.

To recover from this temperature related error, NTC resistor can be added into monitoring

network, as shown in Figure 9.

The monitoring voltage is then driven by the following relationship (neglecting the offset term

for simplicity):

where now the RIMON is the equivalent monitoring resistor and it depends on the

temperature through NTC resistor.

Considering the relationships between IDROOP and the IOUT, the voltage results:

MONITORING

IMON

⋅

IMON

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

DROOP

⋅

REF

IMON

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

⋅

DROOP

DCR

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

OUT

⋅

DROOP

IMON

To GND_core

(Remote Sense)

NTC

CIMON

VREF = +3V3

RIMON_OS

RIMON

To CPU

DROOP

IMON

To GND_core

(Remote Sense)

CIMON

VREF = +3V3

RIMON_OS

RIMON

To CPU

MONITORING

IMON

⋅

IMON

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

DROOP

⋅

IMON

⋅

IMON

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

DCR

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

OUT

⋅⋅

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