MAX8868 MAXIM [Maxim Integrated Products], MAX8868 Datasheet - Page 7

• Manufacturer Part Number: MAX8868
• Description: Low-Noise, Low-Dropout, 150mA Linear Regulators in SOT23
• Manufacturer: MAXIM [Maxim Integrated Products]

An external bypass capacitor connected to the BP pin
reduces noise at the output. Additional blocks include a
current limiter, reverse battery protection, thermal sen-
sor, and shutdown logic. The MAX8868 also includes
an auto-discharge function, which actively discharges
the output voltage to ground when the device is placed
in shutdown mode.
The MAX8867/MAX8868 are supplied with factory-set
output voltages from 2.5V to 5V, in 100mV increments.
Except for the MAX886_EUK29 and the MAX886_EUK32
(which have an output voltage preset at 2.84V and
3.15V, respectively), the two-digit suffix allows the cus-
tomer to choose the output voltage in 100mV increments.
For example, the MAX8867EUK33 has a preset output
voltage of 3.3V. (see Expanded Ordering Information ).
The MAX8867/MAX8868 feature a 1.1Ω typical P-chan-
nel MOSFET pass transistor. This provides several
advantages over similar designs using PNP pass tran-
sistors, including longer battery life. The P-channel
MOSFET requires no base drive, which reduces quies-
cent current considerably. PNP-based regulators waste
considerable current in dropout when the pass transis-
tor saturates. They also use high base-drive currents
under large loads. The MAX8867/MAX8868 do not suf-
fer from these problems and consume only 100µA of
quiescent current whether in dropout, light-load, or
heavy-load applications (see the Typical Operating
Characteristics ).
The MAX8867/MAX8868 include a current limiter, which
monitors and controls the pass transistor’s gate voltage,
limiting the output current to 390mA. For design purposes,
consider the current limit to be 160mA minimum to 500mA
maximum. The output can be shorted to ground for an
indefinite amount of time without damaging the part.
Thermal-overload protection limits total power dissipa-
tion in the MAX8867/MAX8868. 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 20°C, resulting in a pulsed output
during continuous thermal-overload conditions.
Thermal-overload protection is designed to protect the
MAX8867/MAX8868 in the event of fault conditions. For
continual operation, do not exceed the absolute maxi-
mum junction-temperature rating of T
Internal P-Channel Pass Transistor
Thermal-Overload Protection
_______________________________________________________________________________________
J
= +170°C, the thermal sensor
150mA Linear Regulators in SOT23
Output Voltage
J
Current Limit
= +150°C.
Low-Noise, Low-Dropout,
The MAX8867/MAX8868’s maximum power dissipation
depends on the thermal resistance of the case and cir-
cuit board, the temperature difference between the die
junction and ambient air, and the rate of air flow. The
power dissipation across the device is P = I
V
where T
MAX8867/MAX8868 die junction and the surrounding
air,
age, and
printed circuit board, copper traces, and other materi-
als to the surrounding air.
The GND pin of the MAX8867/MAX8868 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 MAX8867/MAX8868 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 dis-
connects 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 conjunction
with an internal 200kΩ resistor, creates a 80Hz lowpass
filter for noise reduction. The MAX8867/MAX8868 exhibit
30µV
and C
power-on circuit that pre-charges the bypass capacitor.
The Typical Operating Characteristics show graphs of
Noise vs. BP Capacitance, Noise vs. Load Current, and
Output Noise Spectral Density.
Normally, use a 1µF capacitor on the MAX8867/
MAX8868’s input and a 1µF to 10µF capacitor on the
output. Larger input capacitor values and lower ESRs
provide 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 capacitance and
__________Applications Information
OUT
Operating Region and Power Dissipation
JB
RMS
). The maximum power dissipation is:
OUT
J
(or
- T
of output voltage noise with C
P
BA
= 10µF. Start-up time is minimized by a
A
MAX
JC
IN
is the temperature difference between the
) is the thermal resistance of the pack-
is the thermal resistance through the
or V
= (T
Reverse Battery Protection
SHDN
J
- T
Capacitor Selection and
A
falls below ground. Their cir-
) / (
Regulator Stability
JB
Noise Reduction
+
BA
)
BP
OUT
= 0.01µF
(V
IN
7
-