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Texas Instruments TSC2005 Power Consumption Under Different Modes Application notes
Application Report
SLAA370 – October 2007
TSC2005 Power Consumption Under Different Mode
Wendy Fang, Tony Chang, and James Wang .......................................................... Precision Analog, HPA
ABSTRACT
This application report discusses the TSC2005 power consumption under different
touch screen operating modes, addresses the function and power of various TSC2005
converting functions and status states, and provides a guideline for using the TSC2005
to perform the required functions and features with the optimal low power consumption.
1
2
3
4
Contents
Introduction .......................................................................................... 2
Power Supply ....................................................................................... 2
TSC2005 Power Consumption.................................................................... 3
Conclusion ......................................................................................... 21
List of Figures
1
2
3
4
5
6
7
8
9
10
11
12
13
14
TSC2005 Touch Screen System Block Diagram ............................................... 2
Power Supply Current With Different Power Supply Voltage for (a) Analog and (b)
Digital Circuitries .................................................................................... 3
Power Supply Current Under Power-Down State .............................................. 6
RIRQ is Connected to Ground (Through the Yellow Line) During the Wait State ........... 7
Power Supply SNSVDD Maximal (a) Current and (b) Power in Wait State ................ 8
Touch Screen Controller Analog Interface Traffic .............................................. 9
Touch Panel Drive Current ...................................................................... 11
TSMode1 With X/Y/Z1/Z2 Converting and Without Batch Delay ........................... 15
TSMode1 With X/Y/Z1/Z2 Converting and With Batch Delay ............................... 16
TSMode1 With X/Y Converting and With Batch Delay ...................................... 17
TSMode2 With X/Y Converting Without Batch Delay ........................................ 18
TSMode2 With X/Y Converting With Batch Delay ............................................ 19
TSMode3 With X/Y Converting .................................................................. 20
TSMode3 With Z1/Z2 Converting ............................................................... 21
List of Tables
1
2
3
4
5
6
7
8
9
TSC2005 ADC Converter Function Selection .................................................. 4
TSC2005 IDCP (in μA) Under SNSVDD = 3.3 VDC and F = 2 MHz ........................ 12
TSC2005 IDCP (in μA) Under SNSVDD = 3.3 VDC and F = 1 MHz ........................ 12
TSC2005 IDCP (in μA) Under SNSVDD = 2.5 VDC and F = 2 MHz ........................ 12
TSC2005 IDCP (in μA) Under SNSVDD = 2.5 VDC and F = 1 MHz ........................ 12
TSC2005 IDCP (in μA) Under SNSVDD = 1.8 VDC and F = 2 MHz ........................ 13
TSC2005 IDCP (in μA) Under SNSVDD = 1.8 VDC and F = 1 MHz ........................ 13
TSC2005 Digital I/O Consumed Current IIOVDD (in μA) ...................................... 14
TSC2005 Operating Modes ...................................................................... 14
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Introduction
1
Introduction
TSC2005 is a 4-wire resistive touch screen controller with an SPI digital interface. In addition to its low
power consumption, the TSC2005 features a small-package, high-ESD level, MAV filtering, batch delay,
self-test, and other advantages.
The TSC2005 is a register-based touch screen controller with full software-programmable features; it can
operate under many different modes by setting its control registers. Although the TSC2005 data sheet
(SBAS379) provides the power consumption ranges, power performance is different under various
TSC2005 converting functions and status states. This application report addresses how to use and
operate the TSC2005 at its highest performance and lowest power consumption during the different
TSC2005 operating modes.
2
Power Supply
To operate the TSC2005 device, power supplies need to be connected to the TSC2005 pins SNSVDD
(+1.6 VDC ~ 3.6 VDC) and IOVDD (+1.2 VDC ~ SNSVDD). The SNSVDD pin receives the power for
driving the touch screen and the TSC2005 internal circuits; and the IOVDD pin receives the power for only
driving the digital I/O interface to the host processor (see Figure 1).
Analog & TSC Circuits Powered by SNSVDD
SNSVDD
Digital IO Powered by IOVDD
IOVDD
SPI bus
Analog Interface
Interrupt
Processor
{
TSC2005
{
Resistive
Touch
Screen
X+, X-, Y+, Y-
Digital Interface
NOTE: The supply voltage on IOVDD must be the same as or lower than SNSVDD.
Figure 1. TSC2005 Touch Screen System Block Diagram
In Figure 1, the blocks inside the blue box are powered by SNSVDD, and those inside the red box draw
current from IOVDD power supply.
Users can use a single power supply for both SNSVDD and IOVDD pins, or use two separated supplies,
whichever is more convenient or practical.
Power consumption is closely related to power supply voltage, as Figure 2 shows. Figure 2 shows only a
power consumption tendency and is the example for a specific operating mode, test conditions, and
settings. For details of the Figure 2 test conditions/settings, see the TSC2005 data sheet (SBAS379).
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(a)
(b)
Figure 2. Power Supply Current With Different Power Supply Voltage
for (a) Analog and (b) Digital Circuitries
Two observations can be made from Figure 2 :
1)The higher the power supply, the higher the consumed current (power).
2) The analog power supply to SNSVDD (Figure 2a) consumes much more power than the digital
power supply to IOVDD (Figure 2b).
The power supply current or power consumption changes with different operating modes, different
configurations, and different control registers settings, as is discussed in the following sections.
3
TSC2005 Power Consumption
This application report focuses on power consumption in different TSC2005 Converting modes, Status
states, and Operating modes.
The Converting mode indicates how the TSC2005 ADC converting is started or initialized. TSC2005
converting is either in the Host Controlled mode or the TSC Controlled mode.
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TSC2005 Power Consumption
The Status state specifies a TSC2005 status and condition, including Power-Down state, Wait state,
Batch-Wait state, Driving/Converting/Processing state, and Reading/Writing state.
The Operating mode is a TSC2005 operating or working sequence, which is the combination of the
selected converting function in the different status states. The TSC2005 Operating mode has been
classified into TSMode1, TSMode2, and TSMode3, as defined in the TSC2005 data sheet (SBAS379).
3.1
Converting Modes
The TSC2005 ADC converter can be initialized by a command from the host processor (host-controlled
converting mode) or automatically when it detects pressure on the touch panel (TSC-controlled converting
mode).
The TSC2005 default converting mode is host controlled. The mode can be changed by setting the PSM
(bit 15) in TSC2005 Configuration Register 0 (CR0). If PSM is set to 0, the TSC2005 is in the
host-controlled converting mode; if the PSM is 1, the converting mode is TSC controlled.
The host-controlled converting mode is valid to perform all types of ADC converter functions listed in
Table 1. The TSC-controlled converting mode, however, can only be used with two touch screen
functions: the X/Y scan or X/Y/Z1/Z2 scan, highlighted in yellow at Table 1.
Table 1. TSC2005 ADC Converter Function Selection
C2
C1
C0
0
0
0
0
Touch screen scan function: X-, Y-, Z-, and Z2-coordinates converted and the results returned to X, Y, Z1, and
Z2 data registers. Scan continues until either the pen is lifted or a stop bit is sent.
0
0
0
1
Touch screen scan function: X- and Y-coordinates converted and the results returned to X and Y data registers.
Scan continues until either the pen is lifted or a stop bit is sent.
0
0
1
0
Touch screen scan function: X-coordinate converted and the results returned to X data register.
0
0
1
1
Touch screen scan function: Y-coordinate converted and the results returned to Y data register.
0
1
0
0
Touch screen scan function: Z1-, and Z2-coordinates converted and the results returned to Z1 and Z2 data
registers.
0
1
0
1
Auxiliary input converted and the results returned to the AUX data register.
0
1
1
0
A temperature measurement is made and the results returned to the Temperature Measurement 1 data
register.
0
1
1
1
A differential temperature measurement is made and the results returned to the Temperature Measurement 2
data register.
1
0
0
0
Auxiliary input is converted continuously, and the results are returned to the AUX data register.
1
0
0
1
Touch screen panel connection to X-axis drivers is tested. The test result is output to PINTDAV and shown in
STATUS register.
1
0
1
0
Touch screen panel connection to Y-axis drivers is tested. The test result is output to PINTDAV and shown in
STATUS register.
1
0
1
1
RESERVED (Note: any condition caused by this command can be cleared by setting the STS bit to 1).
1
1
0
0
Touch screen panel short-circuit (between X and Y plates) is tested through Y-axis. The test result is output to
PINTDAV and shown in the STATUS register.
1
1
0
1
Turn on X+, X– drivers
1
1
1
0
Turn on Y+, Y– drivers
1
1
1
Turn on Y+, X– drivers
1
(1)
(2)
FUNCTION (1) (2)
C3
Set with bits 6 ~3 in control byte 1 (CB1).
See TSC2005 data sheet (SBAS379).
In the host-controlled converting mode, the touch system works with the following sequence:
- when the touch panel is pressed, the TSC senses the touch and sends a PENIRQ interrupt to the host;
- the host receives the interrupt from the TSC, and responses to the TSC in the order based on its tasks
and priority;
- the host then sends the 8-bit CB1 (Control Byte 1) to the TSC and specifies which converting function in
Table 1 should start;
- after receiving the command from the host, the TSC starts powering the corresponding driver and
converting the signal.
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Obviously, some wait occurs at TSC2005 between the time a touch is sensed on the panel and before
TSC2005 starts a conversion.
In the TSC-controlled mode, on other hand, the touch system works in a different sequence:
- after power up or RESET, the host programs the TSC into either a X/Y or X/Y/Z1/Z2 scan function, that
is, the C3-C0 (in Table 1) is set to 0000b or 0001b;
- when the touch panel is pressed, the TSC senses the touch and starts the corresponding conversion
automatically and immediately;
- the TSC sends an interrupt to the host after all data is ready to be read, and the host thus reads the data
registers.
Compared to the host-controlled converting mode, the TSC-controlled converting mode does not wait for
the host to response and starts the touch data converting whenever the panel is touched. The TSC2005
can produce thousands of sets of coordinates in its TSC-controlled converting mode if a touch continues
to press on the panel.
However, the TSC's fast converting function may not be necessary in real-world applications. For
example, most touch screen applications need only 100 to 500 sets of good touch data per second for
human interfacing. Thus, the advantage of the host-controlled converting mode is apparent because the
host can control the time and interval of the TSC2005 driving/sampling and samples only needed touch
data sets; therefore, this eliminates unnecessary current for driving the touch panel, reduces the analog
interface traffic, and reduces the system power consumption.
Furthermore, the advanced Batch-Delay feature of TSC2005 can perform even better. With the TSC2005
Batch-Delay feature in its TSC-controlled converting mode, TSC2005 can control the time and interval of
the touch screen samples, taking over the task from the host and thus not only reducing analog interface
traffic, but also reducing digital interface traffic and saving resources at the host. For additional details
about the Batch-Delay feature, see the TSC2005 data sheet (SBAS379).
3.2
Status States
The power consumption of the different TSC2005 status states varies. To optimize TSC2005 performance
and reduce power consumption, an understanding of the TSC2005 main status states and their power
consumption can benefit the user.
3.2.1
Power-Down State
Besides physically turning off power to the TSC2005, the next best power-saving state is to bring the
TSC2005 into its power-down or sleeping state, which consumes very low current, typically in
nanoamperes (nA) (see Figure 3), See the specifications in the TSC2005 data sheet.(SBAS379).
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Figure 3. Power Supply Current Under Power-Down State
TSC2005 enters power-down state after power up or RESET by default, and returns to the power-down
state whenever the TSC2005 ADC is stopped.
3.2.2
Wait State
The wait state occurs only under the host-controlled converting mode and between the times after the
panel is touched and before the host sends a command to TSC2005 (see Section 3.1).
In the host-controlled converting mode, the TSC2005 PINTDAV pin should be programmed as PENIRQ or
PENIRQ AND DAV, by bits 15-14 of CR2 (Configuration Register 2). Thus, the TSC2005 can detect
whether the panel is touched or not, and sends the PENIRQ interrupt to the host whenever the panel is
touched.
During the wait state, the power is mainly consumed by the internal pullup resistor RIRQ, which is
approximately 51 kΩ or 90 kΩ (programmble). See Figure 4.
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Figure 4. RIRQ is Connected to Ground (Through the Yellow Line) During the Wait State
When the panel is not pressured, the X- and Y-layers of the touch panel are separated and thus no circuit
is connected between the SNSVDD and its ground SNSGND. A touch on the panel connects the X- and
Y-layer at the point A ( Figure 4), and an electric loop starts from the SNSVDD pin, through the internal
pullup resistor RIRQ and through the touch panel and point A, to the ground SNSGND, as shown by the
yellow line in Figure 4.
The power consumption at wait state changes with the touch location on the panel. The approximate
maximal current for RIRQ = 51-kΩ:
V
I wait*max ^ SNSVDD .
51000
(1)
And approximate maximal power consumption is:
P wait*max ] VSNSVDD VSNSVDDń51000.
(2)
Where VSNSVDD is the SNSVDD voltage, Iwait-max is the maximal wait-state current drawing from SNSVDD;
and Pwait-max the maximal wait-state power consumption from the SNSVDD. Figure 5 shows the current
and power during the wait state, under RIRQ = 51-kΩ, from a different SNSVDD value.
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(a)
(b)
Figure 5. Power Supply SNSVDD Maximal (a) Current and (b) Power in Wait State
In the wait state, the consumed current is less than 31.4 μA for the minimal SNSVDD (1.6 VDC) and less
than 70.6 μA for the maximal SNSVDD (3.6 VDC), as shown in Figure 5(a).
3.2.3
Batch-Wait State
The batch-wait state occurs only in the TSC-controlled converting mode and with the batch-delay timing
being set larger than 0 ms, by BDT2 ~ BDT0, D2~D0 of CFR1 (Configuration Register 1). The TSC2005
batch delay can be programmed to 1 ms, 2 ms, 4 ms 10 ms, 20 ms, 40 ms, or 100 ms, corresponding to
1000, 500, 250, 100, 50, 25 or 10 SSPS (sample sets per second). For additional information, see the
TSC2005 data sheet (SBAS379).
Batch delay is a feature that allows the TSC2005 to control the time interval between two sets of touch
screen data. With batch delay, the TSC2005 drives and samples the touch data in a fixed interval (batch
delay) while a touch keeps pressure on the panel.
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……
Driving Y/X/Z1/Z2
Driving Y/X/Z1/Z2
……
(a)
Driving Y/X/Z1/Z2
Batch-Wait ...
(b)
NOTE: a) Touch screen controller keeps driving, sampling, and converting X, Y, Z1, and Z2 data at a rate of
1/(274 μs) = 3650 sets per second without Batch Delay. b) The rate is controllable and the analog interface
traffic is greatly reduced with Batch Delay. Where Ch1 is X+; Ch2 is X–, Ch3 is Y+, and Ch4 is Y–.
Figure 6. Touch Screen Controller Analog Interface Traffic
As previously discussed, in the TSC-controlled converting mode, the TSC2005 starts to drive, sample, and
convert X /Y or X/Y/Z1/Z2 as soon as a touch is sensed on the panel. If the touch remains on the panel
without any batch delay, the TSC2005 continuously drives the touch panel and samples and converts the
data. Thus, the touch panel is powered up/down without stopping, and the traffic on the analog interface
continues and becomes heavy, as shown by Figure 6(a).
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On other hand, with the batch delay, the TSC enters the batch-wait state after the first processed sample
set is completed and stays in it until the end of the batch-delay time, even though the pen touch is still
detected during the entire time. Therefore, the panel driver is not unnecessarily on, ADC conversion is
eliminated during the batch delay, the analog interface traffic is reduced, and power is saved.
During the Batch-Wait state, the current from SNSVDD is a function of VSNSVDD or
I batch*wait + ƒȀǒVSNSVDDǓ
(3)
and Ibatch-wait is less than 100 μA with VSNSVDD = 3.3 VDC, consisting of:
– power for an internal batch-delay timer
– the current through the PINTDAV pullup resistor, i.e., the Equation 1 as discussed in Section 3.2.2.
3.2.4
DCP State
The DCP (Driving/Converting/Processing) state is for acquiring touch screen data, such as X/Y/Z. It is the
highest power-consuming period or state. To get touch screen data, the TSC2005 powers on the touch
panel, converts the sampled voltage into digital data, and preprocesses the touch data if the MAVF is
programmed ON. The TSC2005 SNSVDD provides the power under the DCP state.
The power consumed from SNSVDD consists of two parts: internal by the TSC2005 device itself and
external by driving the touch panel and the analog interface. That is:
I DCP + I Internal ) I External
(4)
Where: IInternal is the current used by TSC2005 internal SAR ADC, system clocks, and other processing
circuits, such as the PENIRQ circuit shown in Figure 4. Thus, IInternal can be expressed by a function of
VSNSVDD or
I Internal + ƒǒVSNSVDDǓ
(5)
The ƒ( VSNSVDD ) can be affected by temperature and may vary a little from part to part.
Example 1: Some experiential data with a TSC2005EVM shows that: in the fully operational DCP state,
the TSC2005 internal DCP current under SNSVDD = 3.3 VDC is approximately 900 μA and that under
SNSVDD = 2.5 VDC is approximately 680 μA. Using a first-order curve fit produces the following equation:
ƒǒV SNSVDDǓ ^ k
V SNSVDD
and
k ^ 0.2724
10 3.
(6)
To drive the touch panel, TSC2005 consumes IExternal from SNSVDD power supply. The IExternal is decided
by:
– SNSVDD voltage
– the touch panel resistance
– the ratio of the driver's power ON and OFF timing.
The peak or maximal panel driving current IExternal-max (= VSNSVDD / Rtouch) has been shown in Figure 7,
where the Rtouch is the touch panel average resistance. For example, if the resistance between a touch
panel's X+ and X- pins is 600 Ω and that between Y+ and Y- is 400 Ω, the Rtouch is 500 Ω (= (600+400)/2).
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NOTE: The touch screen is driven by the touch screen controller; the panel resistance Rtouch determines the peak
drive current from the touch screen controller from the SNSVDD power supply.
Figure 7. Touch Panel Drive Current
Figure 7 considers only the ideal TSC driving condition where the TSC's internal driving ON resistance
has been ignored (because it is small compared to the touch panel's resistance). Thus, the actual power
consumption in this case should be a little less than that shown in Figure 7.
The average external current within a second is:
V
I External + I External*max t + SNSVDD SSPS S
Rtouch
F
B
(7)
Where τ = SSPS × S × B/F, the driving–ON time per second. SSPS is sample sets per second that
indicates how many sets of touch data the host gets within a second; S is the number of data in a set of
samples; B is the TSC resolution, either 10 bit or 12 bit; and F is ADC clock frequency, which can be 4, 2,
or 1 MHz.
The number of data in a set of samples, or the S in Equation 6, is the total number of samples in a set.
For example, if the needed touch coordinates consist of X and Y, and the MVA filter is disabled, then S =
2, an X and a Y data. If needing X, Y, Z1, and Z2 (with MVA filter still disabled), S = 4; and if needing X,
Y, Z1, and Z2 and with MVA filter enabled, S = 4 × N, where N is the filter's window width.
In Equation 7, the TSC2005 programmable parameter PVS (panel voltage stabilization) delay time is set
to 0 μs, so as to simplify the discussion. The PVS delay (>0 μs) adds touch driver ON time prior to ADC
sampling and thus more SNSVDD power is consumed (see SLAA362).
Example 2: Using a TSC2005EVM to measure the power consumption with the condition that:
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VSNSVDD = 3.3, 2.5, or 1.8 VDC
Rtouch = 450 Ω
SSPS = 100, 250, or 500
S = 4, 12, 28, or 60
B = 12 bit
F = 1 or 2 MHz
Table 2 to Table 7 list the measured IDCP, on a TSC2005EVM, and the modeled IDCP, by using Equation 5
and Equation 7 .
Table 2. TSC2005 IDCP (in μA) Under SNSVDD = 3.3 VDC and F = 2 MHz
SSPS = 500
SSPS = 250
SSPS = 100
Measured
Modeled
Measured
Modeled
Measured
Modeled
S = 4 (Read X/Y/Z and N=1)
1000
987
940
943
900
917
S = 12 (Read X/Y/Z and N=3)
1250
1163
1070
1031
960
952
S = 28 (Read X/Y/Z and N=7)
1610
1515
1240
1207
1030
1022
S = 60 (Read X/Y/Z and
N=15)
2320
2219
1600
1559
1170
1163
Table 3. TSC2005 IDCP (in μA) Under SNSVDD = 3.3 VDC and F = 1 MHz
SSPS = 500
SSPS = 250
SSPS = 100
Measured
Modeled
Measured
Modeled
Measured
S = 4 (Read X/Y/Z and N=1)
1080
1075
980
987
920
Modeled
934
S = 12 (Read X/Y/Z and N=3)
1490
1427
1190
1162
1000
1005
S = 28 (Read X/Y/Z and N=7)
2170
2131
1520
1515
1140
1145
S = 60 (Read X/Y/Z and
N=15)
3490
3539
2220
2219
1400
1427
Table 4. TSC2005 IDCP (in μA) Under SNSVDD = 2.5 VDC and F = 2 MHz
SSPS = 500
SSPS = 250
SSPS = 100
Measured
Modeled
Measured
Modeled
Measured
Modeled
S = 4 (Read X/Y/Z and N=1)
710
748
670
714
640
694
S = 12 (Read X/Y/Z and N=3)
910
881
770
781
680
721
S = 28 (Read X/Y/Z and N=7)
1240
1148
900
914
750
774
S = 60 (Read X/Y/Z and
N=15)
1880
1681
1180
1181
880
881
Table 5. TSC2005 IDCP (in μA) Under SNSVDD = 2.5 VDC and F = 1 MHz
SSPS = 500
12
SSPS = 250
SSPS = 100
Measured
Modeled
Measured
Modeled
Measured
Modeled
S = 4 (Read X/Y/Z and N=1)
780
814
700
748
660
707
S = 12 (Read X/Y/Z and N=3)
1150
1081
880
881
730
761
S = 28 (Read X/Y/Z and N=7)
1740
1614
1130
1148
860
868
S = 60 (Read X/Y/Z and
N=15)
2930
2681
1650
1681
1090
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Table 6. TSC2005 IDCP (in μA) Under SNSVDD = 1.8 VDC and F = 2 MHz
SSPS = 500
SSPS = 250
SSPS = 100
Modeled
Modeled
Modeled
S = 4 (Read X/Y/Z and N=1)
538
514
500
S = 12 (Read X/Y/Z and N=3)
634
562
519
S = 28 (Read X/Y/Z and N=7)
826
658
558
S = 60 (Read X/Y/Z and N=15)
1210
850
634
Table 7. TSC2005 IDCP (in μA) Under SNSVDD = 1.8 VDC and F = 1 MHz
SSPS = 500
SSPS = 250
SSPS = 100
Modeled
Modeled
Modeled
S = 4 (Read X/Y/Z and N=1)
586
538
506
S = 12 (Read X/Y/Z and N=3)
778
634
548
S = 28 (Read X/Y/Z and N=7)
1162
826
625
S = 60 (Read X/Y/Z and N=15)
1930
1210
778
The above examples show how TSC2005 touch driving power consumption is effected by SSPS, S, and
F, as well as SNSVDD power voltage. To reduce TSC2005 power consumption, users can focus on these
factors and properly select SSPS, S, F, and SNSVDD based on the system requirement.
3.2.5
SCP State
Section 3.2.4 discussed the DCP state for touch screen data. This section is addressing the same process
for nontouch data (such as AUX). The state is denoted as the SCP or Sampling/Converting/Processing
state. During SCP state, the TSC2005 samples the nontouch input, converts the voltage, and
preprocesses the data if programmed ON.
Compared to DCP state, the SCP state requires no panel driving for nontouch input. Thus, the SCP state
is similar to the IInternal in Equation 7 and usually consumes much less power than the DCP state.
The SCP state is not discussed further in this application report because its focus is on touch screen
modes and power consumption.
3.2.6
R/W State
The R/W state concerns only digital interface and digital power consumption.
Another power supply, IOVDD, is used to provide power for the digital interface while the host is
reading/writing (R/W) from/to the TSC2005 through the SPI bus. The IOVDD power consumption is
usually 100s or even 1000s of times smaller than the SNSVDD power consumption.
The digital I/O current is positively proportional to the IOVDD voltage and positively proportional to the
digital bus traffic density. This relationship can be expressed approximately by:
K
I IOVDD ^ IOVDD VIOVDD SSPS
F IOVDD
(8)
Where IIOVDD is the current drawing from IOVDD under the R/W state; kIOVDD is a constant that can be
affected by temperature and may change from part to part; VIOVDD is IOVDD voltage and ranges from 1.2
VDC to 3.6 VDC; SSPS is the Sample Sets Per Second as previously discussed; and FIOVDD is the SPI
clock (SCLK) frequency. The faster SCLK can transfer the same amount of data within a shorter time,
reduce digital interface time, and thus consume less IOVDD power.
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TSC2005 Power Consumption
Example 3: Using a TSC2005EVM to measure the IOVDD power consumption with the same conditions
listed in Example 2, with VIOVDD = 3.3, 2.5, or 1.8 VDC and SSPS = 100, 250, or 500. The EVM is plugged
into the TI USB-MODEVM board where a C8052 core processor (TAS1020B USB controller) is running
and controlling the SPI. Table 9 lists the measured IIOVDD, and the modeled IIOVDD by using Equation 8
with
K IOVDD
^ 1
1650
F IOVDD
(9)
Table 8. TSC2005 Digital I/O Consumed Current IIOVDD (in μA)
SSPS = 500
SSPS = 250
SSPS = 100
SSPS = 50
Measured
Modeled
Measured
Modeled
Measured
Modeled
Measured
Modeled
VIOVDD = 3.3 VDC
0.9 ~ 1.1
1
0.6
0.5
0.3
0.20
0.2
0.100
VIOVDD = 2.5 VDC
0.7 ~ 0.9
0.76
0.3 ~ 0.6
0.38
0.1 ~ 0.3
0.15
<0.1
0.076
VIOVDD = 1.8 VDC
–
0.55
–
0.27
–
0.11
–
0.055
VIOVDD = 1.2 VDC
–
0.48
–
0.24
–
0.10
–
0.049
Comparing with SNSVDD power consumption, the digital interface power IOVDD consumes much less
power. It is even lower when the digital traffic is lower.
3.3
Touch Screen Operating Modes
After users select TSC2005 ADC converting mode and set up TSC2005 control bytes and configuration
registers, TSC2005 can be placed into one of its three touch screen operating modes, TSMode1,
TSMode2, and TSMode3, as defined in the TSC2005 data sheet (SBAS379).
Table 9 summarizes the operating modes that correspond to the PSM bit and C3-C0 settings.
Table 9. TSC2005 Operating Modes
Operating Mode
PSM
(D15 of CR0)
C3 C2 C1 C0
(D6-D3 of CB1)
TSMode1
PSM = 1b
(TSC-Controlled Converting Mode)
C3~C0 = 0000b (X/Y/Z1/Z2 scan function)
C3~C0 = 0001b (X/Y scan function )
TSMode2
PSM = 0b
(Host-Controlled Converting Mode)
C3~C0 = 0000b (X/Y/Z1/Z2 scan function)
C3~C0 = 0001b (X/Y scan function )
TSMode3
PSM = 0b
(Host-Controlled Converting Mode)
C3~C0 = 0010b (X scan function)
C3~C0 = 0011b (Y scan function )
C3~C0 = 0100b (Z1/Z2 scan function)
TSMode1 is always in the TSC-controlled converting mode. That is, the ADC is initialized to start work and
be controlled by TSC. There are two types of conditions: without the batch delay and with the batch delay.
Without the batch delay, the TSMode1 sequence includes Power-Down, DCP, and R/W status states, as
the example that is shown in Figure 8. With the batch delay, the TSMode1 consists of Power Down, Batch
Wait, DCP, and R/W status states, as the examples that are shown in Figure 9 and Figure 10.
TSMode2 is similar to TSMode1 but is in the Host-Controlled converting mode. This means that the ADC
is initialized to start work by the host responding to the PENIRQ interrupt from the TSC and then
controlled by the TSC thereafter. The two types of conditions are without the batch delay and with the
batch delay. Without the batch delay, its sequence includes Power Down, Wait, DCP, and R/W status
states, as the example shown in Figure 11. With the batch delay, it consists of Power Down, Wait, Batch
Wait, DCP, and R/W status states, as the example shown in Figure 12.
TSMode3 is under the Host-Controlled converting mode totally. This means that the ADC is initialized to
start work by the host and is controlled by the host. The sequence includes Power Down, Wait, DCP, and
R/W status states, as the examples that are shown in Figure 13 and Figure 14.
14
TSC2005 Power Consumption Under Different Modes
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TSC2005 Power Consumption
Status Modes
and Supply
Current
/PINTDAV Pin
Digital Interface
and Host Activity
Figure 8 through Figure 14 provide the TSC2005 power consumption under the various touch screen
operating modes. See the previous sections on the SNSVDD and IOVDD current consumed, under each
specific status states.
Touch
On
Initialization
(PSM=1,
C3~C0=0000,
BDT=000 )
...
/PINTDAV
Triggered
All Data Have
been Read
Host Read
X,Y,Z1&Z2
/CS = “1” (SPI Deactived)
Touch
Released
/PINTDAV All Data Have
Triggered been Read
Host Read
X,Y,Z1&Z2
...
...
/PINTDAV = /PENIRQ & DAV
PINTS 1 ~ 0 = 00b
...
/PINTDAV = /DAV
PINTS1 ~ 0 = 01b or 11b
...
/PINTDAV = /PENIRQ
PINTS 1 ~ 0 = 10b
Power-Down State
DCP
for Y
Check & Find
Touch Released
Check & Find
Touch still On
Touch On
DCP
for X
DCP
for Z1& Z2
DCP
for Y
DCP
for X
...
...
DCP
for Z1&Z2
Power-Down State
...
Supply Current
Power-Down State (3.2.1)
SNSVDD Current
DCP State (3.2.4)
R/W State ( 3.2.6)
IOVDD Current
Figure 8. TSMode1 With X/Y/Z1/Z2 Converting and Without Batch Delay
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Status Modes
and Supply
Current
/PINTDAV Pin
Digital Interface
and Host Activity
TSC2005 Power Consumption
Touch
On
Initialization
(PSM=1,
C3~C0=0000
BDT>000)
...
/PINTDAV
Triggered
All Data Have
been Read
Host Read
X,Y,Z1&Z2
/CS = “1” (SPI Deactived)
/PINTDAV = /PENIRQ&DAV
PINTS1 ~ 0 = 00b
/PINTDAV = /DAV
PINTS1 ~ 0 = 01b or 11b
/PINTDAV = /PENIRQ
PINTS1 ~ 0 = 10b
...
...
...
...
...
...
...
...
Check & Find
Touch Still ON
Touch On
Power-Down State
DCP
for Y
DCP
for X
DCP
for Z1& Z2
...
Batch-Wait State
...
DCP
for Y
DCP
for X
...
DCP
for Z1&Z2
...
...
Supply Current
Power-Down State (3.2.1)
SNSVDD Current
Batch Wait State (3.2.3)
DCP State (3.2.4)
R/W State (3.2.6)
IOVDD Current
Figure 9. TSMode1 With X/Y/Z1/Z2 Converting and With Batch Delay
16
TSC2005 Power Consumption Under Different Modes
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Status Modes
and Supply
Current
/PINTDAV Pin
Digital Interface
and Host Activity
TSC2005 Power Consumption
Touch
On
Initialization
(PSM=1
C3~C0=0001
BDT > 000)
/PINTDAV
Triggered
/CS = “1” (SPI Deactived)
/PINTDAV
Triggered
All Data Have
been Read
Host
Read
X &Y
All Data Have
been Read
Host
Read
X &Y
/CS = “1” (SPI Deactived)
Touch
Released
...
...
/PINTDAV = /PENIRQ & DAV
PINTS1 ~ 0 = 00b
...
/PINTDAV = /DAV
PINTS1 ~ 0 = 01b or 11b
...
/PINTDAV = /PENIRQ
PINTS1 ~ 0 = 10b
Check & Find
Touch still On
Touch On
Power-Down State
DCP
for Y
DCP
for X
Batch-Wait State
DCP
for Y
Check & Find
Touch Released
DCP
for X
Batch Wait
State
...
PowerDown State
...
Supply Current
Power-Down State (3.2.1)
Batch Wait State (3.2.3)
SNSVDD Current
IOVDD Current
DCP State (3.2.4)
R/W State (3.2.6)
Figure 10. TSMode1 With X/Y Converting and With Batch Delay
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Status Modes
and Supply
Current
/PINTDAV Pin
Digital Interface
and Host Activity
TSC2005 Power Consumption
Touch
On
Initialization
(PSM=0 &
BDT=000)
/CS = “1”
(SPI Deactived)
/PINTDAV
Triggered
Set X/Y
Scan
Mode
/CS = “1”
(SPI Deactived)
All Data Have /PINTDAV
been Read
Triggered
All Data Have
been Read
Host
Read
X &Y
Host
Read
X &Y
...
Touch
Released
/CS = “1”
(SPI Deactived)
...
/PINTDAV = /PENIRQ & DAV
PINTS 1 ~ 0 = 00b
...
/PINTDAV = /DAV
PINTS1 ~ 0 = 01b or 11b
...
/PINTDAV = /PENIRQ
PINTS 1 ~ 0 = 10b
Check & Find
Touch still On
Touch On
Power-Down State
Wait State
DCP
for Y
DCP
for X
DCP
for Y
DCP
for X
...
DCP
for Y
DCP
for X
PowerDown
...
Supply Current
Power-Down State (3.2.1)
Wait State (3.2.2)
SNSVDD Current
IOVDD Current
DCP State (3.2.4)
R/W State (3.2.6)
Figure 11. TSMode2 With X/Y Converting Without Batch Delay
18
TSC2005 Power Consumption Under Different Modes
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Status Modes
and Supply
Current
/PINTDAV Pin
Digital Interface
and Host Activity
TSC2005 Power Consumption
Touch
On
Initialization
(PSM=0 &
BTD > 000)
/CS = “1”
(SPI Deactived)
/PINTDAV
Triggered
Set X/Y
Scan
Mode
/CS = “1”
(SPI Deactived)
Touch
Released
All Data Have
been Read
Host
Read
X &Y
...
/CS = “1”
(SPI Deactived)
...
/PINTDAV = /PENIRQ & DAV
PINTS1 ~ 0 = 00b
...
/PINTDAV = /DAV
PINTS1 ~ 0 = 01b or 11b
...
/PINTDAV = /PENIRQ
PINTS1 ~ 0 = 10b
Check & Find
Touch still On
Touch On
Power-Down State
Wait State
DCP
for Y
DCP
for X
Batch Wait State
Check & Find
Touch Off
DCP
for Y
...
PowerDown
...
Supply Current
Power-Down State (3.2.1)
Wait State (3.2.2)
SNSVDD Current
IOVDD Current
Batch Wait State (3.2.3)
DCP State (3.2.4)
R/W State (3.2.6)
Figure 12. TSMode2 With X/Y Converting With Batch Delay
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Status Modes
and Supply
Current
/PINTDAV Pin
Digital Interface
and Host Activity
TSC2005 Power Consumption
Touch
On
Initialization
PSM=0
/CS = “1”
(SPI Deactived)
/PINTDAV
Triggered
Set X
Scan
Mode
/CS = “1”
(SPI Deactived)
X Data has
been Read
Host
Read
X
Set Y
Scan
Mode
Y Data has
been Read
/PINTDAV
Triggered
/CS = “1”
(SPI Deactived)
Host
Read
Y
...
Touch
Released
/CS = “1”
(SPI Deactived)
...
/PINTDAV = /PENIRQ & DAV
PINTS1 ~ 0 = 00b
...
/PINTDAV = /DAV
PINTS1 ~ 0 = 01b or 11b
...
/PINTDAV = /PENIRQ
PINTS1 ~ 0 = 10b
Check & Find
Touch still On
Touch On
Power-Down State
Wait State
DCP
for X
Wait State
DCP
for Y
Wait State
...
Wait State
PowerDown
...
Supply Current
Power-Down State (3.2.1)
Wait State (3.2.2)
SNSVDD Current
IOVDD Current
DCP State (3.2.4)
R/W State (3.2.6)
Figure 13. TSMode3 With X/Y Converting
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Status Modes
and Supply
Current
/PINTDAV Pin
Digital Interface
and Host Activity
Conclusion
Touch
On
Initialization
PSM=0
/CS = “1”
(SPI Deactived)
Z Data has
been Read
/PINTDAV
Triggered
Set Z
Scan
Mode
/CS = “1”
(SPI Deactived)
Host Host
Read Read
Z1
Z2
Set Z
Scan
Mode
/PINTDAV
Triggered
Z Data has
been Read
Host Host
ReadRead
/CS = “1”
(SPI Deactived) Z1 Z2
...
Touch
Released
/CS = “1”
(SPI Deactived)
...
/PINTDAV = /PENIRQ & DAV
PINTS1 ~ 0 = 00b
...
/PINTDAV = /DAV
PINTS1 ~ 0 = 01b or 11b
...
/PINTDAV = /PENIRQ
PINTS1 ~ 0 = 10b
Check & Find
Touch still On
Touch On
Power-Down State
Wait State
DCP
for Z1 & Z2
DCP
for Z1 & Z2
Wait State
Wait State
...
Wait State
PowerDown
...
Supply Current
Power-Down State (3.2.1)
Wait State (3.2.2)
SNSVDD Current
IOVDD Current
DCP State (3.2.4)
R/W State (3.2.6)
Figure 14. TSMode3 With Z1/Z2 Converting
4
Conclusion
This application report discusses the TSC2005 power consumption in different operating modes so as to
provide a guideline for using the TSC2005 to perform the required functions and features with optimal
low-power consumption.
A touch screen system can be set up to operate in one of the three touch screen operating modes,
TSMode1, TSMode2, or TSMode3. During any one of the touch screen operating modes, the power
consumptions are greatly varied during different periods (or status states). One of the main power
consumption is during the DCP state, provided from the SNSVDD supply that is expressed by Equation 4.
Users can reduce the power consumption during the DCP state with selected touch panel (resistance) and
SNSVDD voltage, and reduce the time under the DCP state by reducing the touch panel power ON time,
applying host-controlled converting mode or, better, applying TSC-controlled converting mode with the
batch-delay feature.
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