![NXP Semiconductors MC9S12VRP64 Owner Reference Manual Download Page 509](http://html.mh-extra.com/html/nxp-semiconductors/mc9s12vrp64/mc9s12vrp64_owner-reference-manual_1721842509.webp)
ADC Electrical Specifications
MC9S12VRP Family Reference Manual Rev. 1.3
NXP Semiconductors
509
is recommended to configure port AD pins as outputs only for low frequency, low load outputs. The impact
on ADC accuracy is load dependent and not specified. The values specified are valid under condition that
no port AD output drivers switch during conversion.
C.1.1.2
Source Resistance
Due to the input pin leakage current as specified in conjunction with the source resistance there will be a
voltage drop from the signal source to the ADC input. The maximum source resistance R
S
specifies results
in an error (10-bit resolution) of less than 1/2 LSB (2.5 mV) at the maximum leakage current. If device or
operating conditions are less than worst case or leakage-induced error is acceptable, larger values of source
resistance of up to 10Kohm are allowed.
C.1.1.3
Source Capacitance
When sampling an additional internal capacitor is switched to the input. This can cause a voltage drop due
to charge sharing with the external and the pin capacitance. For a maximum sampling error of the input
voltage
1LSB (10-bit resolution), then the external filter capacitor, C
f
1024 * (C
INS
–C
INN
).
C.1.1.4
Current Injection
The following points should be considered.
1. A current is injected into the channel being converted. The channel being stressed has conversion
values of 0x3FF (in 10-bit mode) for analog inputs greater than V
RH
and 0x000 for values less than
V
RL
unless the current is higher than specified as disruptive condition.
2. Current is injected into pins in the neighborhood of the channel being converted. A portion of this
current is picked up by the channel (coupling ratio K), This additional current impacts the accuracy
of the conversion depending on the source resistance.
The additional input voltage error on the converted channel can be calculated as:
V
ERR
= K * R
S
* I
INJ
with I
INJ
being the sum of the currents injected into the two pins adjacent to the converted channel.
3. The HVI pins do not include the diode structures that inject current when the input goes outside the
supply-ground range. Thus the HVI pin current injection is limited to below 200uA. However if
the HVI impedance converter bypass is enabled, then even currents in this range can corrupt ADC
results from simultaneous conversions on other channels. This can be prevented by disabling the
bypass, either by clearing the PTAENLx or PTABYPLx bit.
4. Similarly, when the ADC is converting an HVI pin voltage, then the impedance converter bypass
must be disabled to ensure that current injection on PADx pins does not impact the HVI ADC
conversion result.
Summary of Contents for MC9S12VRP64
Page 16: ...MC9S12VRP Family Reference Manual Rev 1 3 16 NXP Semiconductors ...
Page 46: ...Device Overview S12VRP Series MC9S12VRP Family Reference Manual Rev 1 3 46 NXP Semiconductors ...
Page 236: ...S12S Debug Module S12DBGV2 MC9S12VRP Family Reference Manual Rev 1 3 236 NXP Semiconductors ...
Page 244: ...Interrupt Module S12SINTV1 MC9S12VRP Family Reference Manual Rev 1 3 244 NXP Semiconductors ...
Page 358: ...Timer Module TIM16B2CV3 MC9S12VRP Family Reference Manual Rev 1 3 358 NXP Semiconductors ...
Page 436: ...Supply Voltage Sensor BATSV2 MC9S12VRP Family Reference Manual Rev 1 3 436 NXP Semiconductors ...
Page 528: ...NVM Electrical Parameters MC9S12VRP Family Reference Manual Rev 1 3 528 NXP Semiconductors ...
Page 530: ...Package Information MC9S12VRP Family Reference Manual Rev 1 3 530 NXP Semiconductors ...
Page 531: ...Package Information MC9S12VRP Family Reference Manual Rev 1 3 NXP Semiconductors 531 ...
Page 532: ...Package Information MC9S12VRP Family Reference Manual Rev 1 3 532 NXP Semiconductors ...