ISL68124IRAZ datasheet(14/46 Pages) RENESAS

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ISL68124

FN8796 Rev.2.00

Page 14 of 46

June 16, 2017

connected to the ISL68124 TMON1 pin. The reported

temperature is that of the highest temperature SPS of the group.

In addition to the external temperature sense, the IC senses its

own die temperature, which can be monitored through

PowerNavigator.

Sensed temperature is used in the system for faults, telemetry,

and temperature compensation of sensed current.

Temperature Compensation

The ISL68124 supports inductor DCR sensing, which generally

requires temperature compensation due to the copper wire used

to form inductors. Copper has a positive temperature coefficient

of approximately 0.39%/°C. Because the voltage across the

inductor is sensed for the output current information, the sensed

current has the same positive temperature coefficient as the

inductor DCR.

Compensating current sense for temperature variation generally

requires that the current sensing element temperature and its

temperature coefficient is known. Although temperature

coefficient is generally obtained easily, actual current sense

element temperature is essentially impossible to measure

directly. Instead, a temperature sensor (a BJT for the ISL68124)

placed near the inductors is measured and the current sense

element (DCR) temperature is calculated from that

measurement. Calculating current sense element temperature is

equivalent to applying gain and offset corrections to the

temperature sensor measurement. The ISL68124 supports both

corrections.

Figure 14 depicts the block diagram of temperature

compensation. A BJT placed near the inductors used for DCR

sensing is monitored by the IC using the well known delta Vbe

method of temperature sensing. TSENSE is the direct measured

temperature of the BJT. Because the BJT is not directly sensing

DCR, corrections must be made so that TDCR reflects the true

DCR temperature. Corrections are applied according to the

relationship shown in Equation 1, where kSLOPE represents a

gain scaling and TOFFSET represents an offset correction. These

parameters are provided by the designer using the

PowerNavigator GUI:

After TDCR has been determined, the compensated DCR value

can be determined according to Equation 2, where DCR25 is the

DCR at +25°C and TC is the temperature coefficient of copper

(3900 ppm/°C). TDCR = TACTUAL here:

Thus, the temperature compensated DCR is now used to

determine the actual value of current in the DCR sense element.

In the physical PCB design, the temperature sense diode (BJT) is

placed close to the inductor of the phase that is never dropped

during automatic phase drop operation. Additionally, a filter

capacitor no larger than 500pF should be added near the IC

between each TEMPx pin and VCCS. This is shown in Figure 15.

Lossless Input Current and Power Sensing

Input current telemetry is provided using an input current

synthesizer. By using the IC’s ability to precisely determine its

operational conditions, input current can be synthesized to a high

degree of accuracy without the need for a lossy sense resistor.

Fine-tuning of offset and gain are provided for in the GUI. Note

that input current sense fine-tuning must be done after output

current sense setup is finalized. With a precise knowledge of

input current and voltage, input power can be computed.

Input current and power telemetry is accessed using PMBus and

easily monitored in the PowerNavigator GUI.

TDCR

kSLOPE TSENSE TOFFSET



(EQ. 1)

DCRCORR

DCR25 1TC

TACTUAL 25

–









(EQ. 2)

FIGURE 14. BLOCK DIAGRAM OF TEMPERATURE COMPENSATION

Vbe

VCCS

TMONx

TOFFSET

TSENSE

VOUT

DCR

CURRENT

SENSE

IPHASE#

TEMPERATURE

COMPENSATION

DCRCORR

TO TELEMETRY

CSx

CSRTNx

kSLOPE

IPHASE#

SW1

SW2

SW3

Output 1

SW0

Output 0

TMON1

VCCS

TMON0

OPTIONAL AUXILIARY

TEMPERATURE SENSE

OPTIONAL AUXILIARY

TEMPERATURE SENSE

FIGURE 15. RECOMMENDED PLACEMENT OF TEMPERATURE

SENSORS

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