Datasheet

47 nF
R
TH
R
T
R
B
REG50
TS+
TS–
R
B TH@40C TH@90C
= 0.4 (R – R )
R
T
= R
TH@ 40C
– 2R
TH @90C
– R
B
bq76PL536-Q1
www.ti.com SLUSAB1 –MAY 2011
Figure 5. Thermistor Connection
Converting TSn Result to Voltage (Ratio)
To convert the returned TSn measurement value to a ratio, R
TS
= V
TS
: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 = (V
TSn
/ REG50 × scalar) – OFFSET
TS1: R
TS1
= ((TEMPERATURE1_H × 256 + TEMPERATURE1_L) + 2) / 33,046
TS2: R
TS2
= ((TEMPERATURE2_H × 256 + TEMPERATURE2_L) + 9) / 33,068
Example:
The voltage connected to the TS1 inputs (TS1+ – TS1–) == 0.661 V; V
REG50
≈ 5 V nominal
After conversion, REG
MSB
== 0x11; REG
LSB
== 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
ADC Band-Gap Voltage Reference
The ADC and protection subsystems use separate and independent internal voltage references. The ADC
bandgap (V
REF
) is nominally 2.5 V. The reference is temperature-compensated and stable.
The internal reference is brought out to the VREF pin for bypassing. A high quality 10-μF capacitor should be
connected between the VREF and AGND pins, in very close physical proximity to the device pins, using short
track lengths to minimize the effects of track inductance on signal quality. The AGND pin should be connected to
VSS. Device VSS connections should be brought to a single point close to the IC to minimize layout-induced
errors. The device tab should also be connected to this point, and is a convenient common VSS location. The
internal VREF should not be used externally to the device by user circuits.
Conversion Control
Convert Start
Two methods are available to start a conversion cycle. The CONV_H pin may be asserted, or firmware may set
the CONVERT_CTRL[CONV] bit.
Copyright © 2011, Texas Instruments Incorporated 17