C8051F040/1/2/3/4/5/6/7
74 Rev. 1.5
6.2. High-Voltage Difference Amplifier
The High-Voltage Difference Amplifier (HVDA) can be used to measure high differential voltages up to
60 V peak-to-peak, reject high common-mode voltages up to ±60 V, and condition the signal voltage range
to be suitable for input to ADC0. The input signal to the HVDA may be below AGND to –60 volts, and as
high as +60 volts, making the device suitable for both single and dual supply applications. The HVDA pro-
vides a common-mode signal for the ADC via the High Voltage Reference Input (HVREF), allowing mea-
surement of signals outside the specified ADC input range using on-chip circuitry. The HVDA has a gain of
0.05 V/V to 14 V/V. The first stage 20:1 difference amplifier has a gain of 0.05 V/V when the output ampli-
fier is used as a unity gain buffer. When the output amplifier is set to a gain of 280 (selected using the
HVGAIN bits in the High Voltage Control Register), an overall gain of 14 can be attained.
The HVDA uses four available external pins: +HVAIN, –HVAIN, HVCAP, and HVREF. HVAIN+ and HVAIN-
serve as the differential inputs to the HVDA. HVREF should be used to provide a common mode reference
for input to ADC0, and to prevent the output of the HVDA circuit from saturating. The output from the
HVDA circuit as calculated by Equation 6.1 must remain within the “Output Voltage Range” specification
listed in Table 6.3. The ideal value for HVREF in most applications is equal to 1/2 the supply voltage for the
device. When the ADC is configured for differential measurement, the HVREF signal is applied to the AIN-
input of the ADC, thereby removing HVREF from the measurement. HVCAP facilitates the use of a capac-
itor for noise filtering in conjunction with R7 (see Figure 6.3 for R7 and other approximate resistor values).
Alternatively, the HVCAP could also be used to access amplification of the first stage of the HVDA at an
external pin. (See Table 6.3 on page 90 for electrical specifications of the HVDA.)
Equation 6.1. Calculating HVDA Output Voltage to AIN+
Figure 6.3. High Voltage Difference Amplifier Functional Diagram
V
OUT
HVAIN+HVAIN-–Gain HVREF+=
Note: The output voltage of the HVDA is selected as an input to the AIN+ input of ADC0 via its analog multiplexer
(AMUX0). HVDA output voltages outside the ADC’s input range will result in saturation of the ADC input. Allow
for adequate settle/tracking time for proper voltage measurements.
k
5k
100k
5k
HVA0CN
Gain Setting
HVAIN-
HVAIN+
HVREF
HVCAP
Vout
(To AMUX0)
5k
Resistor values are
approximate
