BQ76PL536APAPR datasheet(19/74 Pages) TI1

19 / 74 page

47 nF

RTH

REG50

TS+

TS–

TH@40C

TH@90C

= 0.4 (R

– R

)

RT = RTH@ 40C – 2RTH @90C – RB

bq76PL536A

www.ti.com

SLUSAD3B – JUNE 2011 – REVISED JANUARY 2016

Feature Description (continued)

7.3.1.5 Temperature Measurement

The bq76PL536A can measure the voltage TS1+, TS1– and TS2+, TS2– differential inputs using the ADC. An

external thermistor or resistor divider network typically drives these inputs. The TSn inputs use the REG50 output

divided down and internally connected as the ADC reference during conversions. This produces a ratiometric

result and eliminates the need for compensation or correction of the REG50 voltage drift when used to drive the

temperature sensors. The REG50 reference allows an approximate 2.5-V full-scale input at the TSn inputs. The

final reading is limited between 0 and 16383, corresponding to an external ratio of 0 to 0.5.

Two control bits are required for the ADC to convert the TSn input voltages successfully. ADC_CONTROL[TSn]

is set to cause the ADC to convert the TSn channel on the next requested conversion cycle. IO_CONTROL[TSn]

is set to cause the FET switch connecting the TSn– input to VSS to close, completing the circuit of the voltage

divider. The IO_CONTROL bits should only be set as needed to conserve power; at high temperatures,

thermistor excitation current may be relatively high.

7.3.1.5.1

External Temperature Sensor Support (TS1+, TS1–, TS2+, and TS2–)

The device is intended for use with a nominal 10 k

Ω at 25ºC NTC external thermistor (AT103 equivalent) such as

the Panasonic ERT-J1VG103FA, a 1% device. A suitable external resistor-capacitor network should be

connected to position the response of the thermistor within the range of interest. This is typically RT= 1.47 kΩ

and RB = 1.82 kΩ (1%) as shown in Figure 14. A parallel bypass capacitor in the range 1 nF to 47 nF placed

across the thermistor should be added to reduce noise coupled into the measurement system. The response

time delay created by this network should be considered when enabling the respective TS input prior to

conversion and setting the OT delay timer. See Figure 14 for details.

Figure 14. Thermistor Connection

7.3.1.5.2

Converting TSn Result to Voltage (Ratio)

To convert the returned TSn measurement value to a ratio, RTS = VTS:REG50, the following formulas are used.

The setting FUNCTION_CONFIG = 0100 xxxxb is assumed. Note that the offset and gain correction are slightly

different for each channel.

ADC behavior: COUNT = (VTSn / REG50 × scalar) – OFFSET

(4)

TS1: RTS1 = ((TEMPERATURE1_H × 256 + TEMPERATURE1_L) + 2) / 33,046

(5)

Example:

The voltage connected to the TS1 inputs (TS1+ – TS1–) == 0.661 V; VREG50 ≈ 5 V nominal

After conversion, REGMSB == 0x11; REGLSB == 0x16

ACTUAL_COUNT = 0x11 × 0x100 + 0x16 = 0x1116 (4374.)

(4374 + 2) / 33,046 = 0.1324 (ratio of TSn inputs to REG50)

0.1324 × REG50 = 0.662 V

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