PT2000 datasheet(53/148 Pages) NXP

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NXP Semiconductors

PT2000

6.7.2.1

Negative current differential amplifier

The key characteristic of the second differential amplifier is it works at negative differential input voltages and therefore has a negative

gain. This is used to detect overcurrent when the low-side is Off.

The current threshold can be calculated using the following formula.

DAC_VALUE is selected and changed at runtime by the digital microcore by means of the signal dacx_value (3:0).

VDAC LSB is the DAC resolution = 156.25 mV.

VDA_BIAS is the fixed voltage biasing applied to the differential amplifier output = 250 mV.

The Gain Value GDA_DIFF is fixed to -2.0.

RSENSEX is the external sense resistor of the current measurement channel x.

6.7.2.2

Current measurement offset compensation

The analog offset compensation for the differential amplifier 5 and 6 of channel 5 and 6 is done in the same way for channel 1 to 4. The

DAC5/6L and the signal Cur5/6l_fbk are used for the offset compensation. Since the accuracy is not actually critical to detect the

overcurrent, the differential amplifier 5 and 6 negative do not have offset compensation (see Figure 19).

6.8

OA_x output pins, multiplexer and T & H

6.8.1

General features

The output signals of the six current sensing amplifiers are available via three external pins OA_1, OA_2, and OA_3 of the device (refer

to Figure 20). With the OAGainx (1:0) and OAxG1 signal, it is possible to select between five different output gains. This feature is used

to adapt the device to an ADC input range of 3.3 V or 5.0 V, and also to add the possibility of amplifying the output signal even higher for

some special measurement functions. The maximum output voltage at the OA_x pins of VCC5 always has to be taken into account.

For the two higher gains of 3.0 and 5.33, the bias voltage of nominal 250 mV of the input signal is removed before amplifying the signal

and adding again to the amplified signal afterwards.

The OA1/2/3 output pins includes the possibility of switching to hi-impedance mode to enable the direct connection of two of these output

pins to one micro-controller ADC input. All OA_x output multiplexers can also be switched to VCC2P5 as a third option. This is used to

check the connection between the PT2000 and the microcontroller ADC on the ECU level.

Table 31. Boost overcurrent sense amplifier overall gain

Gain value

Normal differential mode input voltage Full scale range current with 10 m

Ω shunt

DAC resolution with 10 m

Ω shunt

-2.0

-1047 mV …0

-104.7 A

-7.81 A

Table 32. OA_x amplifier gain selection and output voltage

Oagainx(1:0)

OAxG1

Gain value

Output voltage

d.c.

1.0

VIN * Gain

1.33

VIN * Gain

2.0

VIN * Gain

3.0

(VIN – 250 mV) * Gain +250 mV

5.33

(VIN – 250 mV) * Gain +250 mV

DACVALUE

VDACLSB

() 250mV

–

()

GDADIFF RSENSE

⋅

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