Features: 4-wire touch screen interface
LCD noise reduction feature (STOPACQ pin)
Automatic conversion sequencer and timer
User-programmable conversion parameters
On-chip temperature sensor: −40°C to +85°C
On-chip 2.5 V reference
On-chip 8-bit DAC
3 auxiliary analog inputs
1 dedicated and 3 optional GPIOs
2 direct batterymeasurement channels (0.5V to 5 V)
3 interrupt outputs
Touch-pressuremeasurement
Wake up on touch function
Specified throughput rate of 125 kSPS
Single supply, VCC of 2.7V to 5.25 V
Separate VDRIVElevel for serial interface
Shutdown mode: 1 µAmaximum
32-leadLFCSP 5 mm x 5mm package Application-Personal digital assistants
-Smart hand-held devices
-Touch screen monitors
-Point-of-sale terminals
-Medical devices
-Cell phones
-Pagers Pinout
Specifications
| Parameter |
Rating |
| VCC to GND |
-0.3V to +7V |
| Analog Input Voltage to GND |
-0.3V to VCC +0.3V |
| Digital Input Voltage to GND |
-0.3V to VCC +0.3V |
| Digital Output Voltage to GND |
-0.3V to VCC +0.3V |
| VREF to GND |
-0.3V to VCC +0.3V |
|
Input Current to Any Pin Except Supplies, |
10mA |
|
ESD Rating |
2.5KV |
| Operating Temperature Range |
-40 to +85 |
| Storage Temperature Range |
-65 to +150 |
| Junction Temperature |
150 |
| LFCSP package |
|
| Power Dissipation |
450mW |
| JA Thermal Impedance |
135.7/W |
| IR Reflow Peak Temperature |
220 |
| Pb-Free Parts Only |
260(±0.5) |
| Lead Temperature(Soldering 10s) |
300 |
| Resolution (Bits) |
12bit |
| T-Put Rate |
125kSPS |
| # Chan |
9 |
| Supply V |
Single(+3),Single(+3.3) |
| Pwr Diss (max) |
3.2mW |
| Interface |
Ser |
| Ain Range |
Uni (Vref),Uni 2.5V |
| SNR (dB) |
n/a |
| Pkg Type |
CSP |
DescriptionThe AD7877 is a 12-bit successive approximation ADC witha synchronousserialinterfaceandlowonresistance switchesfor driving touch screens.The AD7877 operates froma single2.7 V to5.25 V power supply(functional operation to2.2V),and features throughputrates of125 kSPS.The AD7877 features directbatterymeasurement on two inputs,temperature and touch-pressuremeasurement.
The AD7877 alsohas anon-boardreference of2.5 V. When not in use,it can beshut down to conservepower.An external reference can alsobeapplied and can bevariedfro1 V to+VCC,while the analog input range is from0 V to VREF. The device includes a shutdo wnmode,which reduces its current consumption tolessthan1 µA.
Toreduce the effects ofnoise fromLCDs,the acquisition phase oftheon-board ADC canbecontrolledviathe STOPACQpin.User-programmable conversioncontrols include variable acquisition timeand first conversiondelay.Upto16 averages can be taken per conversion.There is alsoanon-boardDAC for LCD backlig ht orcontrastcontrol.The AD7877 can run in either slave or master mode,using a conversion sequencer and timer.Itis ideal for battery-powered systems suchas personal digital assistants with resistive touch screens and other portable equipment.
The partis available in a 32-leadlead frame chipscale package (LFCSP).
AD7877 Data Sheet
