to case) is the thermal resistance of the package cho-

sen, and

through the PC board, copper traces, and other materi-

als to the surrounding air. Figure 5 shows the allowable

power dissipation for typical PC boards at +25°C,

+50°C, and +70°C ambient temperatures.

The MAX8869 TSSOP-EP package features an

exposed thermal pad on its underside. This pad lowers

the package’s thermal resistance by providing a direct

thermal heat path from the die to the PC board.

Additionally, GND also channels heat. Connect the

exposed thermal pad and GND to circuit ground by

multiple vias to the ground plane.

Applications Information

Capacitor Selection and

Regulator Stability

Capacitors are required at the MAX8869 input and out-

put. Connect 1µF or greater capacitors between IN and

MAX8869’s relatively high bandwidth, use only surface-

mount ceramic capacitors that have low equivalent

series resistance (ESR) and high self-resonant frequen-

cy (SRF). Make the input and output traces at least

2.5mm wide (the width of the four parallel inputs and

IC to minimize the impact of PC board trace induc-

tance. The width of the ground trace should be maxi-

mized underneath the IC to ensure a good connection

between GND and the ground side of the capacitors.

The output capacitor’s ESR and SRF can affect stability

and output noise. Use capacitors with greater than 5MHz

SRF and ESR of 60mΩ or less to ensure stability and

optimum transient response. This is particularly true in

applications with very low output voltage (<2V) and high

output current (>0.5A).

Since some capacitor dielectrics may vary over bias

voltage and temperature, consult the capacitor manu-

facturer specifications to ensure that the capacitors

meet these requirements over all voltage and tempera-

ture conditions used.

Soft-Start Capacitor Selection

the MAX8869 output current to slowly rise during start-

up, reducing stress on the input supply. The rise time to

10nF to 100nF, with a 5V rating, are sufficient.

Because this ramp is applied to the current-limit com-

parator, the actual time for the output voltage to ramp

up depends on the load current and output capacitor.

Leave SS open to disable soft-start.

Input-Output (Dropout) Voltage

A regulator’s minimum input-to-output voltage differen-

tial (dropout voltage) determines the lowest usable sup-

ply voltage. In battery-powered systems, this

determines the useful end-of-life battery voltage. Since

a 0.2Ω P-channel MOSFET is used as the pass device,

current (see

Voltage vs. Output Current in

Typical Operating

remains low in dropout.

Noise, PSRR, and Transient Response

The MAX8869 is designed to achieve low dropout volt-

age and low quiescent current in battery-powered sys-

tems while still maintaining good noise, transient

response, and AC rejection (see PSRR vs. Frequency

in the

Typical Operating Characteristics). When operat-

ing from very noisy sources, supply noise rejection and

transient response can be improved by increasing the

values of the input and output capacitors and employ-

ing passive postfiltering. MAX8869 output noise is typi-

Typical Operating Characteristics).

1A, Microcap, Low-Dropout,

Linear Regulator

_______________________________________________________________________________________

9

Figure 5. Power Operating Region: Maximum Output Current

vs. Input-Output Differential Voltage

0

0.6

0.4

0.2

0.8

1.0

1.2

1

03

24

5

INPUT-OUTPUT DIFFERENTIAL VOLTAGE

MAXIMUM CONTINUOUS CURRENT

°C

°C

°C

°C