Output Voltage

The MAX8877/MAX8878 are supplied with factory-set

output voltages from 1.5V to 5.0V, in 100mV increments.

Except for the MAX887_EUK29 and the MAX887_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 MAX8877EUK33 has a preset output

voltage of 3.3V (see Expanded Ordering Information).

Internal P-Channel Pass Transistor

The MAX8877/MAX8878 feature a 1.1

Ω typical

P-channel MOSFET pass transistor. This provides sever-

al 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 transistor

saturates. They also use high base-drive currents under

large loads. The MAX8877/MAX8878 do not suffer from

these problems and consume only 100µA of quiescent

current whether in dropout, light-load, or heavy-load

applications (see the Typical Operating Characteristics).

Current Limit

The MAX8877/MAX8878 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

Thermal-overload protection limits total power dissipa-

tion in the MAX8877/MAX8878. When the junction tem-

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-

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

The maximum power dissipation is:

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.

Reverse Battery Protection

The MAX8877/MAX8878 have a unique protection

scheme that limits the reverse supply current to 1mA

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 Reduction

An external 0.01µF bypass capacitor at BP, in conjunc-

tion with an internal 200k

Ω resistor, creates a 80Hz low-

pass filter for noise reduction. The MAX8877/MAX8878

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.

____________Applications Information

Capacitor Selection and

Regulator Stability

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

≥

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

increase the capacitance by a factor of 2 or more to

ensure stability at temperatures below -10°C. With X7R or

X5R dielectrics, 1µF should be sufficient at all operating

≥ 2.5V. A graph of the Region of

Low-Noise, Low-Dropout, 150mA Linear

Regulators with '2982 Pinout

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