SA58603 Datasheet, PDF (11/15 Pages) NXP Semiconductors – High precision operational amplifier, comparator, and voltage reference

Philips Semiconductors
High precision operational amplifier,
comparator, and voltage reference
Product data
SA58603
APPLICATION INFORMATION
Typical gas pilot detection circuit
Figure 31 shows a typical application of the SA58603 in which the
input amplifier is driven by a thermocouple heated by the pilot flame
in a water heater or gas burner. The circuit comparator may be
programmed to detect when the pilot is out. The IC is operated from
a single voltage supply making it capable of battery backup with loss
of AC power. It may be operated from a one-cell Lithium battery or
two alkaline cells. 10 nF bypass capacitors are placed from V_CC and
reference voltage output (pin 6) to ground to filter power supply
noise and interference from external noise sources.
Selecting external components
Gain
Recommended amplifier gain is 40 dB. The gain is is set by the
combination of R1, R2, and R3 as shown in the following equations:
Av
+
(R3 ) R2)
R3
;
Av
(dB)
=
20
log
(Av);
R3
=
R1
k
R2
For a gain of 40 dB, Av = 100 V/V;
if R2 = 1 kΩ, then 99*R3 = 1 kΩ; R3 = 10.1 Ω.
R3
+
R1
(R1
)
R2
R2)
;
R3
×
R1
+
R3
×
R2
=
R1
×
R2:
R3 × R2 = R1 (R2 – R3)
Thus
R1
+
R3
(R2
*
R2
R3)
+
10.2W
Comparator output pull-up resistor
The comparator output pull-up resistor is determined by the
following formula:
ǒ Ǔ _{VCC * VSAT(max)}
R+
I_O(sink)(min)
where V_SAT(max) = 400 mV, and I_O(sink)(min) = 5 mA.
Comparator threshold voltage
The comparator threshold voltage is determined by R4 and R5.
They form a voltage divider from the reference voltage output (V_S,
Pin 6) to ground. In the application example, V_COMP, the comparator
input (COMPIN–, Pin 5) is connected to the junction of R4 and R5.
The input level is calculated by following relationship:
V_COMP + 1.27V
R5
(R4 ) R5)
THERMOCOUPLE
AMPLIFIER OUTPUT
ADC TO INPUT
3
R2
R1
2
1
R3
V_CC
8
AMPLIFIER
R
22 kΩ
1.27 V
COMPARATOR
PULL-UP
RESISTANCE
7
COMPARATOR
RESISTANCE
4
V_COMP 6
5
R5
R4
GND
Figure 31. Typical flame detection circuit.
TO ADC AV_REF
TO ADC AV_SS
SL01537
2002 Nov 13
11