PIC17C756A-33/L Microchip Technology Inc., PIC17C756A-33/L Datasheet - Page 189

• Manufacturer Part Number: PIC17C756A-33/L
• Description: 68 PIN, 32 KB OTP, 902 RAM, 50 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC17C756A-33/L

• A/d Inputs: 12-Channel, 10-Bit
• Cpu Speed: 8.25 MIPS
• Eeprom Memory: 0 Bytes
• Input Output: 52
• Interface: I2C/SPI/USART
• Memory Type: OTP
• Number Of Bits: 8
• Package Type: 68-pin PLCC
• Programmable Memory: 32K Bytes
• Ram Size: 902 Bytes
• Speed: 16 MHz
• Timers: 2-8-bit, 2-16-bit
• Voltage, Range: 3-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part

16.7
In systems where the device frequency is low, use of
the A/D RC clock is preferred. At moderate to high fre-
quencies, T
lator.
The absolute accuracy specified for the A/D converter
includes the sum of all contributions for quantization
error, integral error, differential error, full scale error, off-
set error, and monotonicity. It is defined as the maxi-
mum deviation from an actual transition versus an ideal
transition for any code. The absolute error of the A/D
converter is specified at < ±1 LSb for V
the device’s specified operating range). However, the
accuracy of the A/D converter will degrade as V
diverges from V
For a given range of analog inputs, the output digital
code will be the same. This is due to the quantization of
the analog input to a digital code. Quantization error is
typically ± 1/2 LSb and is inherent in the analog to dig-
ital conversion process. The only way to reduce quan-
tization error is to increase the resolution of the A/D
converter or oversample.
Offset error measures the first actual transition of a
code versus the first ideal transition of a code. Offset
error shifts the entire transfer function. Offset error can
be calibrated out of a system or introduced into a sys-
tem through the interaction of the total leakage current
and source impedance at the analog input.
Gain error measures the maximum deviation of the last
actual transition and the last ideal transition adjusted
for offset error. This error appears as a change in slope
of the transfer function. The difference in gain error to
full scale error is that full scale does not take offset error
into account. Gain error can be calibrated out in soft-
ware.
Linearity error refers to the uniformity of the code
changes. Linearity errors cannot be calibrated out of
the system. Integral non-linearity error measures the
actual code transition versus the ideal code transition,
adjusted by the gain error for each code.
Differential non-linearity measures the maximum actual
code width versus the ideal code width. This measure
is unadjusted.
The maximum pin leakage current is specified in the
Device Data Sheet electrical specification (Table 20-2,
parameter #D060).
In systems where the device frequency is low, use of
the A/D RC clock is preferred. At moderate to high fre-
quencies, T
lator. T
minimized to reduce inaccuracies due to noise and
sampling capacitor bleed off.
2000 Microchip Technology Inc.
AD
A/D Accuracy/Error
must not violate the minimum and should be
AD
AD
should be derived from the device oscil-
should be derived from the device oscil-
DD
.
DD
= V
REF
(over
REF
In systems where the device will enter SLEEP mode
after the start of the A/D conversion, the RC clock
source selection is required. In this mode, the digital
noise from the modules in SLEEP are stopped. This
method gives high accuracy.
16.8
If the input voltage exceeds the rail values (V
by greater than 0.3V, then the accuracy of the conver-
sion is out of specification.
An external RC filter is sometimes added for anti-
aliasing of the input signal. The R component should be
selected to ensure that the total source impedance is
kept under the 10 k recommended specification. Any
external components connected (via hi-impedance) to
an analog input pin (capacitor, zener diode, etc.) should
have very little leakage current at the pin.
16.9
The transfer function of the A/D converter is as follows:
the first transition occurs when the analog input voltage
(V
FIGURE 16-7:
AIN
3FFh
3FEh
003h
002h
001h
000h
) equals Analog V
Connection Considerations
Transfer Function
Analog Input Voltage
A/D TRANSFER
FUNCTION
REF
PIC17C7XX
/ 1024 (Figure 16-7).
DS30289B-page 189
SS
or V
DD
)