bq76PL536APAP datasheet(16/60 Pages) TI

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bq76PL536A

SLUSAD3A – JUNE 2011 – REVISED AUGUST 2012

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The GPAI measurement can be configured to use one of two references via FUNCTION_CONFIG[GPAI_REF].

Either the internal bandgap (VREF) or REG50 can be selected. When REG50 is selected, the ADC returns a ratio

of the voltage at the inputs and REG50, removing the need for compensation of the REG50 voltage accuracy or

drift when used as a source to excite the sensor. When the device is configured to measure VBAT

(FUNCTION_CONFIG[GPAI_SRC]

1),

the

device

selects

VREF

automatically

and

ignores

the

FUNCTION_CONFIG[GPAI_REF] setting.

Converting GPAI Result to Voltage

To convert the returned GPAI measurement value to a voltage using the internal band-gap reference

(FUNCTION_CONFIG[GPAI_REF] = 1), the following formula is used.

mV = (REGMSB × 256 + REGLSB) × 2500 / 16,383

FUNCTION_CONFIG[] = 0100 xxxxb

Example:

The voltage connected to the GPAI inputs == 1.25 V;

After conversion, REG_01 == 0x20; REG_02 == 0x00

0x20 × 0x100 + 0x00 = 0x2000 (8192.)

8192 × 2500 / 16,383 = 1250 mV

Converting VBAT Result to Voltage

To convert the returned VBAT measurement value to a voltage, the following formula is used.

V = (REGMSB × 256 + REGLSB) × 33.333 / 2

14 (33.333 ≈ 6.25 / 0.1875)

FUNCTION_CONFIG[] = 0101 xxxxb

Example:

The sum of the series cells connected to VC6–VC0 == 20.295 V;

After conversion, REG_01 == 0x26; REG_02 == 0xf7

0x26 × 0x100 + 0xf7 = 0x26f7 (9975.)

9975 × 33.333 / 16,383 = 20.295 V

Temperature Measurement

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

These inputs are typically driven by an external thermistor/resistor divider network. 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 16,383, 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.

External Temperature Sensor Support (TS1+, TS1– and TS2+, 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 5. 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 5 for details.

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