ISL68134IRAZ datasheet(14/50 Pages) RENESAS

14 / 50 page

ISL68134

FN8817 Rev.1.00

Page 14 of 50

Jun 19, 2017

SPS CURRENT SENSING

SPS current sense is accomplished by sensing each SPS IMON

output individually using VCCS as a common reference. Connect

all SPS IREF input pins and all ISL68134 CSRTNn input pins

together and tie them to VCCS, then connect the SPS IMONn

output pins to the corresponding ISL68134 CSn input pins. The

signals should be run as differential pairs from the SPS back to

the ISL68134.

Temperature Sensing

The ISL68134 supports temperature sensing through BJT or

smart power stage sense elements. Support for BJT sense

elements uses the well known delta Vbe method and allows up

to two sensors (MMBT3906 or similar) on each temperature

sense input, TMON0 and TMON1. Support for smart power stage

uses a linear conversion algorithm and allows one sensor reading

per pin. The conversion from voltage to temperature for smart

power stage sensing is user programmable through the

PowerNavigator GUI.

SPS temperature sensing measures the temperature dependent

voltage output on the SPS TMON pin. All of the SPS devices

attached to the Output 0 rail have their TMON pins connected to

the ISL68134 TMON0 pin. All of the SPS devices attached to the

Output 1 rail have their TMON pins connected to the ISL68134

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 ISL68134 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 be known. Although the temperature

coefficient is generally obtained easily, the actual current sense

element temperature is essentially impossible to measure

directly. Instead, a temperature sensor (a BJT for the ISL68134)

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 and the ISL68134 supports

both corrections.

Figure 14 on page 15 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). Here, TDCR = TACTUAL

Thus, the temperature compensated DCR is now used to

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

FIGURE 11. DESIRED LOAD TRANSIENT RESPONSE WAVEFORMS

IOUT

VOUT

FIGURE 12. LOAD TRANSIENT RESPONSE WHEN R-C TIME

CONSTANT IS TOO SMALL

IOUT

VOUT

FIGURE 13. LOAD TRANSIENT RESPONSE WHEN R-C TIME

CONSTANT IS TOO LARGE

IOUT

VOUT

TDCR

kSLOPE TSENSE TOFFSET



(EQ. 1)

DCRCORR

DCR25 1TC

TACTUAL 25

–









(EQ. 2)

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