Instrukcja obsługi Microchip TC1173

Microchip Niesklasyfikowane TC1173

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DS00776A-page 1
© 2002 Microchip Technology, Inc.
DC Performance Comparisons of CMOS vs. Bipolar LDOs when
Operating in "Dropout" (VIN = Nominal VOUT) Mode
More and more, battery operated systems are requiring lower
terminal voltages to power internal circuits. Multi-cell designs are
rapidly migrating to single-cell architectures to reduce system cost.
A prime example of this system type is digital cameras, which often
use a single-cell 3.6V Li-Ion battery for their power source. Digital
cameras contain high-speed memory ICs, which require tight
voltage regulation at moderate loads to meet the required timing
parameters of the system. Precision low dropout (LDO) regulator
devices can be used to meet these requirements but in doing so,
the LDO regulators must be able to successfully operate in the
‘dropout’ mode as the battery discharges. Dropout mode is entered
when the input voltage (from the battery source) is equal to the
“nominal output voltage” of the LDO; for example a 3.3V LDO
enters dropout mode when its input voltage at the V
IN pin is equal
to 3.3V. Minimal output voltage droop and minimal LDO power
dissipation are critical to meeting various system performance
parameters and extending the life of the battery.
This application note compares the performance of Microchip
Technology’s TC1015 CMOS family of LDOs to two of its bipolar
counterparts, the National Semiconductor LP2981 and the Micrel
MIC5205. Dropout measurements were taken on three different
popular output voltage options (5.0V, 3.3V, and 3.0V) under
varying load conditions ranging from 10mA to 150mA. All measure-
ments were made at ambient temperature (T
A = +25°C).
Author: Patrick Maresca,
Microchip Technology, Inc.
FIGURE 1: Bipolar vs. CMOS LDO regulator schematics.
Figures 1A and 1B compare the block diagram for a common
bipolar regulator with that of an equivalent regulator fabricated in
CMOS. The supply current to the bipolar device is composed of the
bias current, plus a “ground current” (I
GND) component shown in
Figure 1A, which is a fraction of the output current (determined by
the h
FE of the pass transistor) sunk through the output stage of the
error amplifier. The “ground current” component of the CMOS
regulator shown in Figure 1B is virtually zero, due to the extremely
large drain-to-gate impedance of the CMOS pass transistor.
The circuit shown in Figure 2 was used to measure output voltage
droop and device ground current with loads ranging from 10mA to
100mA (in 10mA increments), 125mA, and 150mA. Both the
TC1015 and the MIC5205 have optional reference bypass capaci-
tor connections from pin four to ground. Measurements were made
with and without a 470pF bypass capacitor on both of these devices
but the output voltage droop and ground current did not vary much
with the bypass capacitor connected (only the data taken without
a bypass capacitor is shown in this application note).
Tables I, II, and III show the performance of the TC1015, LP2981,
and MIC5205 for dropout mode operation. Table I contains the data
taken for 5.0V LDOs, Table II contains the data taken for 3.3V
LDOs, and Table III contains the data taken for 3V LDOs. Notice
that in each case, the ground current and power dissipation for the
+
–
VOUT
VREF
VIN
V
IN
B. CMOS Regulator
IGND = 0
~
+
VOUT
VREF
VIN
A. BiPolar Regulator
IGND = IOUT/hFEQ1
~
Q1
+
–
+
–
–
VIN
© 2002 Microchip Technology, Inc.DS00776A-page 2
FIGURE 2: Dropout mode test circuit.
TC1015 CMOS devices is several orders of magnitude better than
the bipolar LP2981/MIC5205 devices. The TC1015 has a slightly
better output voltage droop in dropout mode than the LP2981 for
all load currents and has slightly better droop performance than the
MIC5205 for load currents up to 60mA. The TC1015 has similar
droop performance compared to the MIC5205 for load currents
between 70mA and 100mA and slightly poorer droop performance
for load currents greater than 100mA. However, the extremely high
power dissipation of the MIC5205 makes it a hazardous liability in
systems where extending battery life is critical. The CMOS archi-
tecture of the TC1015 family tends to be the best fit for these types
of battery powered applications requiring regulators to operate in
the dropout mode.
In battery powered systems requiring lower terminal voltages (such
as digital cameras), LDO regulators must often operate in the
‘dropout’ mode to enhance battery life. The TC1015 series of
CMOS LDOs provide superior performance to bipolar LDOs in
minimizing device power dissipation (through lower ground cur-
rents) when operating in the dropout mode. The TC1015 series has
equivalent if not superior performance to bipolar LDOs in minimiz-
ing output voltage droop (under most load conditions) when
operating in dropout.
1
2
34
5
+
–
VIN
GND
SHDN BYPASS
(NC on LP2981)
VOUT
A
+
–
Ammeter Connection
for Ground Current Measurement
VIN = VOUT Nominal
1 Fµ
10K
Voltmeter Connection
for VIN Measurement Voltmeter Connection
for VOUT Measurement
1 Fµ
RL (varied from 10mA to 150mA)
OPEN
LDO
D.U.T.
A
+
–
Ammeter Connection
for Load Current Measurement
DS00776A-page 3
© 2002 Microchip Technology, Inc.
TABLE 1: 5.0V LDO data in device dropout mode (VIN = nominal VOUT).
µ µ
µ µ
µ
5.0 1.0 1.0 10 4.98 20 57.4 0.287 4.96 40 439 2.20 4.96 40 790 3.95
5.0 1.0 1.0 20 4.96 40 58.3 0.292 4.94 60 569 2.85 4.93 70 878 4.39
5.0 1.0 1.0 30 4.94 60 59.1 0.296 4.92 80 687 3.44 4.92 80 966 4.83
5.0 1.0 1.0 40 4.93 70 59.9 0.299 4.90 100 808 4.04 4.91 90 1082 5.41
5.0 1.0 1.0 50 4.91 90 60.6 0.303 4.88 120 933 4.66 4.89 110 1213 6.07
5.0 1.0 1.0 60 4.89 110 61.4 0.307 4.87 130 1054 5.27 4.88 120 1358 6.79
5.0 1.0 1.0 70 4.88 120 62.1 0.310 4.85 150 1188 5.94 4.87 130 1517 7.59
5.0 1.0 1.0 80 4.86 140 62.8 0.314 4.83 170 1318 6.59 4.87 130 1695 8.47
5.0 1.0 1.0 90 4.85 150 63.3 0.317 4.81 190 1455 7.27 4.86 140 1874 9.37
5.0 1.0 1.0 100 4.83 170 64.0 0.320 4.79 210 1598 7.99 4.85 150 2058 10.29
5.0 1.0 1.0 125 4.78 220 65.3 0.327 4.75 250 1961 9.80 4.83 170 2546 12.73
5.0 1.0 1.0 150 4.73 270 66.6 0.333 4.70 300 2298 11.49 4.81 190 3087 15.43
Notes: * Does not include power dissipated in pass element.
No reference bypass capacitors were used when measuring TC1015 and MIC5205.
TABLE 2: 3.3V LDO data in device dropout mode (VIN = nominal VOUT).
µ µ
µ µ µ
3.3 1.0 1.0 10 3.28 20 58.5 0.193 3.27 30 467 1.54 3.27 30 1166 3.85
3.3 1.0 1.0 20 3.27 30 59.6 0.197 3.24 60 582 1.92 3.25 50 1264 4.17
3.3 1.0 1.0 30 3.25 50 60.4 0.199 3.22 80 693 2.29 3.23 70 1376 4.54
3.3 1.0 1.0 40 3.24 60 61.2 0.202 3.21 90 799 2.63 3.22 80 1497 4.94
3.3 1.0 1.0 50 3.22 80 61.8 0.204 3.19 110 917 3.03 3.21 90 1621 5.35
3.3 1.0 1.0 60 3.21 90 62.3 0.206 3.17 130 1050 3.47 3.20 100 1770 5.84
3.3 1.0 1.0 70 3.19 110 62.9 0.208 3.15 150 1173 3.87 3.19 110 1932 6.38
3.3 1.0 1.0 80 3.17 130 63.4 0.209 3.13 170 1304 4.30 3.18 120 2085 6.88
3.3 1.0 1.0 90 3.16 140 64.7 0.213 3.12 180 1452 4.79 3.18 120 2247 7.41
3.3 1.0 1.0 100 3.14 160 65.0 0.215 3.10 200 1597 5.27 3.17 130 2411 7.96
3.3 1.0 1.0 125 3.09 210 65.5 0.216 3.05 250 1955 6.45 3.15 150 2856 9.42
3.3 1.0 1.0 150 3.04 260 66.2 0.219 3.00 300 2293 7.57 3.13 170 3337 11.01
Notes: * Does not include power dissipated in pass element.
No reference bypass capacitors were used when measuring TC1015 and MIC5205.

Specyfikacje produktu

Marka: Microchip
Kategoria: Niesklasyfikowane
Model: TC1173

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