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BAT
N
B
V
(5 VREF)
2
=
(5-12)
5.7.4.2 Auxiliary Input (Normal Mode) for VBAT
BAT
N
B
V
VREF
2
=
(5-13)
5.7.5
Port Scan
5.7.6
Buffer Mode
TSC2117
Low-Power Audio Codec With Embedded miniDSP, Stereo Class-D
Speaker Amplifier, and Smart Four-Wire Touch-Screen Controller
SLAS550A – APRIL 2009 – REVISED JUNE 2009
www.ti.com
Because the ADC code is 1/5 of the actual voltage value applied at VBAT, the correct value can be found
by multiplying the ADC code by 5. For low voltages of VREF, this function can support voltages from 0 to
(5
× VREF), where the upper voltage limit for VBAT is 6 V, and is also limited by the value listed in
In the battery-voltage measurement mode, the conversion results in an ADC output code of B, where the
voltage at the input pin (VBAT) can be calculated as:
where:
N is the programmed resolution of the SAR ADC.
VREF is the applied external reference voltage.
The default functionality for the VBAT input is similar to AUX1 and AUX2. The useful measurement range
is 0 V to VREF, and the maximum voltage input should be limited to 3.6 V. Because VBAT has an internal
resistor divider, the internal ADC code is scaled down; however, in the normal mode, it is internally scaled
back up in the digital domain, so that the normal transfer function can be realized using the SAR ADC.
Although this mode is supported in 8-bit, 10-bit, and 12-bit modes, the 8-bit mode does not show any
missing codes, whereas the 10-bit and 12-bit mode can have one missing code due to the analog input
scaling and digital output scaling. Therefore, it is recommended to always use 8-bit mode for VBAT.
where,
N is the programmed resolution of the SAR ADC.
VREF is the applied external reference voltage.
The auxiliary input can be monitored continuously in scan mode.
If making voltage measurements on the inputs AUX1, AUX2, and VBAT is desired on a periodic basis,
then the port-scan mode can be used. This mode causes the TSC2117 to sample and convert each of the
auxiliary inputs. At the end of this cycle, all of the auxiliary result registers contain the updated values.
Thus, with one write to the TSC2117, the host can cause three different measurements to be made. Port
scan can be set up by writing to page 3/register 3, bits D5–D2.
Port scan can only be used in host-controlled mode.
See Conversion Time Calculations for the TSC2117,
Section 5.7.9, and Port-Scan Operation,
The TSC2117 supports a programmable buffer mode, which is applicable for both touch-screen-related
conversion (X, Y, Z1, Z2) and nontouch-screen-related conversion (VBAT, AUX1, AUX2, TEMP1,
TEMP2). Buffer mode is implemented using a circular FIFO with a depth of 64. The number of interrupts
required to be serviced by a host processor can be reduced significantly buffer mode. Buffer mode can be
enabled using page 3/register 13, bit D7.
APPLICATION INFORMATION
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