SX8650 Datasheet, PDF (47/56 Pages) Semtech Corporation – World’s Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD

SX8650
World’s Lowest Power & Smallest Footprint 4-wire
Resistive Touchscreen Controller with 15kV ESD
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
An active NIRQ (low) needs to be cleared before any new conversions will occur.
6.6. Coordinate Throughput Rate
When the chip is not set to Automatic mode, the coordinate throughput rate depends on the following factors:
- the I2C communication time
- the conversion time
If the SX8650 is set to Automatic mode then the RATE settling must not be faster than the Raw Conversion Rate (RCR).
RCR(kCPS) = 1000 ⁄ Tconv(us)
6.6.1. I2C Communication Time
The time to read the channel data by I2C depends of the mode set and if the clock is stretched or not.
Mode
Clock Stretching
T_comm(us)
MANUAL
No
T_SU;STA -T_LOW + (29+18*Nchan)*T_SCL
MANUAL
Yes
-T_LOW + (21+18*Nchan)*T_SCL
PENTRIG¹
No
T_SU;STA -T_LOW + (9+18*Nchan)*T_SCL
PENTRIG¹
Yes
-T_LOW + (1+18*Nchan)*T_SCL
1. With the pen always down
Table 13.
The highest throughput will be obtained with a I2C frequency of 400kHz and clock stretching when all channels are
sampled in PENTRIG mode.
The host should react to the NIRQ interrupt signal as quickly as possible by reading the channel data.
6.6.2. Conversion Time
The maximum possible throughput can be estimated with the following equation
Tconv(us) = 47 ⋅ Tosc + N_chan ⋅ (POWDLY + (N_filt – 1) ⋅ SETDLY + (21N_filt + 1) ⋅ Tosc)
with:
- N_filt = {1,3,5,7} based on the order defined for the filter FILT (see Figure 7).
- N_chan = {1,2,3,4,5} based on the number of channels defined in I2CRegChanMsk
- POWDLY = 0.5us to 18.19ms, settling time as defined in I2CRegCtrl0
- SETDLY = 0.5us to 18.19ms, settling time when filtering as defined in I2CRegCtrl2
- Tosc is the oscillator period (555ns +/- 15%)
The Coordinate Rate (CR) and Equivalent Coordinate Rate (ECR) which give the number of coordinates (X, Y, Z1, Z2) is
given below
:
CR(kCPS) = 1000 ⁄ T(us)
ACS Revision V2.15/October 2009
©2009 Semtech Corp.
Page 46
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