TSC2046IPWR datasheet(13/34 Pages) TI2

13 / 34 page

TSC2046

SBAS265G − OCTOBER 2002 − REVISED JANUARY 2008

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The second mode does not require a test temperature

calibration, but uses a two-measurement method to eliminate

the need for absolute temperature calibration and for

achieving 2

°C accuracy. This mode requires a second

conversion with an address of A2 = 1, A1 = 1, and A0 = 1,

with a 91 times larger current. The voltage difference

between the first and second conversion using 91 times the

bias current is represented by Equation (1):

DV + kT

q @ In(N)

where:

N is the current ratio = 91

k = Boltzmann’s constant = 1.3807

× 10−23 J/K

(joules/kelvins).

q = the electron charge = 1.6022

× 10–19 C (coulombs).

T = the temperature in kelvins (K).

This method can provide improved absolute temperature

measurement, but at a lower resolution of 1.6

°C/LSB. The

resulting equation that solves for T is:

@ DV

@ In(N)

where:

∆V = VBE(TEMP1) − VBE(TEMP0) (in mV)

∴ T = 2.573 ⋅ ∆V (in K)

or T = 2.573

⋅ ∆V – 273 (in °C)

NOTE: The bias current for each diode temperature

measurement is only on for 3 clock cycles (during the

acquisition mode) and, therefore, does not add any

noticeable increase in power, especially if the temperature

measurement only occurs occasionally.

BATTERY MEASUREMENT

An added feature of the TSC2046 is the ability to monitor the

battery voltage on the other side of the voltage regulator

(DC/DC converter), as shown in Figure 7. The battery

voltage can vary from 0V to 6V, while maintaining the voltage

to the TSC2046 at 2.7V, 3.3V, etc. The input voltage (VBAT)

is divided down by 4 so that a 5.5V battery voltage is

represented as 1.375V to the ADC. This simplifies the

multiplexer and control logic. In order to minimize the power

consumption, the divider is only on during the sampling

period when A2 = 0, A1 = 1, and A0 = 0 (see Table 1 for the

relationship between the control bits and configuration of the

TSC2046).

+VCC

VBAT

7.5k

Ω

2.5k

Ω

DC/DC

Converter

Battery

0.5V

5.5V

0.125V to 1.375V

2.7V

ADC

Figure 7. Battery Measurement Functional Block

Diagram

(1)

(2)

TSC2046IPWR Datasheet(PDF) 13 Page - Texas Instruments

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