MAX8877 Maxim, MAX8877 Datasheet - Page 7

• Manufacturer Part Number: MAX8877
• Description: Low-Noise / Low-Dropout / 150mA Linear Regulators with 2982 Pinout
• Manufacturer: Maxim

Thermal-overload protection limits total power dissipa-
tion in the MAX8877/MAX8878. When the junction tem-
perature exceeds T
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
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
The maximum power dissipation is:
where T
the MAX8877/MAX8878 die junction and the surround-
ing air,
package, and
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.
The MAX8877/MAX8878 have a unique protection
scheme that limits the reverse supply current to 1mA
when either V
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.
An external 0.01µF bypass capacitor at BP, in conjunc-
tion with an internal 200kΩ resistor, creates a 80Hz low-
pass filter for noise reduction. The MAX8877/MAX8878
exhibit 30µV
0.01µF and C
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.
Operating Region and Power Dissipation
J
JB
- T
P
(or
RMS
A
IN
MAX
OUT
is the temperature difference between
BA
or V
JC
Thermal-Overload Protection
_______________________________________________________________________________________
of output voltage noise with C
= (T
is the thermal resistance through the
= 10µF. This is negligible in most
Low-Noise, Low-Dropout, 150mA Linear
) is the thermal resistance of the
Reverse Battery Protection
SHDN
J
J
= +155°C, the thermal sensor
- T
falls below ground. Their cir-
A
) / (
JB
Noise Reduction
+
J
OUT
= +150°C.
BA
)
(V
IN
Regulators with ‘2982 Pinout
- V
OUT
BP
=
).
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
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 ).
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.
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
____________Applications Information
OUT
Load-Transient Considerations
ESR vs. Load Current is shown in the
Sources Other than Batteries
PSRR and Operation from
Capacitor Selection and
Regulator Stability
7