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參數(shù)資料
| 型號： | MAX8877 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Low-Noise, Low-Dropout, 150mA Linear Regulators with ‘2982 Pinout |
| 中文描述： | 低噪聲、低壓差、150mA線性穩(wěn)壓器，引腳兼容于2982 |
| 文件頁數(shù)： | 7/8頁 |
| 文件大小： | 111K |
| 代理商： | MAX8877 |
T hermal-Overload Protec tion
Thermal-overload protection limits total power dissipa-
tion in the MAX8877/MAX8878. When the junction tem-
perature exceeds T
J
= +155°C, the thermal sensor
signals the shutdown logic, turning off the pass transis-
tor and allowing the IC to cool. The thermal sensor will
turn the pass transistor on again after the IC’s junction
temperature cools by 15°C, resulting in a pulsed output
during continuous thermal-overload conditions.
Thermal-overload protection is designed to protect the
MAX8877/MAX8878 in the event of fault conditions. For
continual operation, do not exceed the absolute maxi-
mum junction-temperature rating of T
J
= +150°C.
Operating Region and Power Dissipation
The MAX8877/MAX8878’s maximum power dissipation
depends on the thermal resistance of the case and circuit
board, the temperature difference between the die junc-
tion and ambient air, and the rate of air flow. The power
dissipation across the device is P = I
OUT
(V
IN
- V
OUT
).
The maximum power dissipation is:
P
MAX
= (T
J
- T
A
) / (
θ
J B
+
θ
BA
)
where T
J
- T
A
is the temperature difference between
the MAX8877/MAX8878 die junction and the surround-
ing air,
θ
J B
(or
θ
J C
) is the thermal resistance of the
package, and
θ
BA
is the thermal resistance through the
printed circuit board, copper traces, and other materi-
als to the surrounding air.
The GND pin of the MAX8877/MAX8878 performs the
dual function of providing an electrical connection to
ground and channeling heat away. Connect the GND
pin to ground using a large pad or ground plane.
Reverse Battery Protec tion
The MAX8877/MAX8878 have a unique protection
scheme that limits the reverse supply current to 1mA
when either V
IN
or V
SHDN
falls below ground. Their cir-
cuitry monitors the polarity of these two pins and discon-
nects the internal circuitry and parasitic diodes when the
battery is reversed. This feature prevents device damage.
Noise Reduc tion
An external 0.01μF bypass capacitor at BP, in conjunc-
tion with an internal 200k
resistor, creates a 80Hz low-
pass filter for noise reduction. The MAX8877/MAX8878
exhibit 30μV
RMS
of output voltage noise with C
BP
=
0.01μF and C
OUT
= 10μF. This is negligible in most
applications. Start-up time is minimized by a power-on
circuit that pre-charges the bypass capacitor. The
Typical Operating Characteristics section shows
graphs of Noise vs. BP Capacitance, Noise vs. Load
Current, and Output Noise Spectral Density.
____________Applic ations Information
Capac itor S elec tion and
Regulator S tability
Normally, use a 1μF capacitor on the MAX8877/
MAX8878’s input and a 1μF to 10μF capacitor on the out-
put. Larger input capacitor values and lower ESRs pro-
vide better supply-noise rejection and line-transient
response. Reduce noise and improve load-transient
response, stability, and power-supply rejection by using
large output capacitors. For stable operation over the full
temperature range and with load currents up to 150mA, a
minimum of 1μF is recommended.
Note that some ceramic dielectrics exhibit large capaci-
tance and ESR variation with temperature. With
dielectrics such as Z5U and Y5V, it may be necessary to
use 2.2μF or more to ensure stability at temperatures
below -10°C. With X7R or X5R dielectrics, 1μF should be
sufficient at all operating temperatures. Also, for high-ESR
tantalum capacitors, 2.2μF or more may be needed to
maintain ESR in the stable region. A graph of the Region
of Stable C
OUT
ESR vs. Load Current is shown in the
Typical Operating Characteristics
Use a 0.01μF bypass capacitor at BP for low output volt-
age noise. Increasing the capacitance will slightly
decrease the output noise, but increase the start-up time.
Values above 0.1μF provide no performance advantage
and are not recommended (see Shutdown Exit Delay
graphs in the Typical Operating Characteristics).
PS RR and Operation from
S ourc es Other than Batteries
The MAX8877/MAX8878 are designed to deliver low
dropout voltages and low quiescent currents in battery-
powered systems. Power-supply rejection is 63dB at
low frequencies and rolls off above 10kHz. See the
Power-Supply Rejection Ratio Frequency graph in the
Typical Operating Characteristics.
When operating from sources other than batteries,
improved supply-noise rejection and transient response
can be achieved by increasing the values of the input
and output bypass capacitors, and through passive fil-
tering techniques. The Typical Operating Charac-
teristics show the MAX8877/MAX8878’s line- and load-
transient responses.
Load-T ransient Considerations
The MAX8877/MAX8878 load-transient response
graphs (see Typical Operating Characteristics) show
two components of the output response: a DC shift
from the output impedance due to the load current
change, and the transient response. Typical transient
M
Low-Noise, Low-Dropout, 150mA Linear
Regulators with ‘2982 Pinout
_______________________________________________________________________________________
7
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