LTC1044AI(Rev0) 데이터 시트보기 (PDF) - Linear Technology
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LTC1044AI Datasheet PDF : 12 Pages
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LTC1044A
APPLICATI S I FOR ATIO
Capacitor Selection
External capacitors C1 and C2 are not critical. Matching
is not required, nor do they have to be high quality or
tight tolerance. Aluminum or tantalum electrolytics are
excellent choices with cost and size being the only
consideration.
Negative Voltage Converter
Figure 6 shows a typical connection which will provide a
negative supply from an available positive supply. This
circuit operates over full temperature and power supply
ranges without the need of any external diodes. The LV
pin (pin 6) is shown grounded, but for V + ≥ 3V it may be
“floated”, since LV is internally switched to ground (pin 3)
for V + ≥ 3V.
The output voltage (pin 5) characteristics of the circuit are
those of a nearly ideal voltage source in series with an 80Ω
resistor. The 80Ω output impedance is composed of two
terms:
1. The equivalent switched-capacitor resistance (see
Theory of Operation).
2. A term related to the on-resistance of the MOS
switches.
At an oscillator frequency of 10kHz and C1 = 10µF, the first
term is:
REQUIV
=
1
(fOSC/2)
×
C1
=
5
×
103
1
× 10
×
10–6
=
20Ω
Notice that the above equation for REQUIV is not a capaci-
tive reactance equation (XC = 1/ωC) and does not contain
a 2π term.
1
8
2
7
3 LTC1044A 6
10µF
4
5
LTC1044A • F06
V+ (1.5V TO 12V)
REQUIRED FOR V+ < 3V
VOUT = – V+
10µF
TMIN ≤ TA ≤ TMAX
Figure 6. Negative Voltage Converter
The exact expression for output resistance is extremely
complex, but the dominant effect of the capacitor is clearly
shown on the typical curves of Output Resistance and
Power Efficiency vs Frequency. For C1 = C2 = 10µF, the
output impedance goes from 60Ω at fOSC = 10kHz to 200Ω
at fOSC = 1kHz. As the 1/(f × C) term becomes large
compared to the switch-on resistance term, the output
resistance is determined by 1/(f × C) only.
Voltage Doubling
Figure 7 shows a two-diode capacitive voltage doubler.
With a 5V input, the output is 9.93V with no load and 9.13V
with a 10mA load. With a 10V input, the output is 19.93V
with no load and 19.28V with a 10mA load.
VIN
(1.5V TO 12V)
1
8
2
7
3 LTC1044A 6
+
Vd
1N5817
Vd
1N5817
+
4
5
REQUIRED
FOR V+ < 3V
+
VOUT = 2(VIN – 1)
10µF
10µF
LTC1044A • F07
Figure 7. Voltage Doubler
Ultra-Precision Voltage Divider
An ultra-precision voltage divider is shown in Figure 8. To
achieve the 0.0002% accuracy indicated, the load current
should be kept below 100nA. However, with a slight loss
in accuracy the load current can be increased.
1
8
2
7
+ C1
3 LTC1044A 6
10µF 4
5
V+/2 ±0.002%
TMIN ≤ TA ≤ TMAX
IL ≤ 100nA
LTC1044A • F08
+
REQUIRED FOR
C2
V+ < 6V
10µF
V+ (3V TO 24V)
Figure 8. Ultra-Precision Voltage Divider
7
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