MAX8869 MAXIM [Maxim Integrated Products], MAX8869 Datasheet - Page 9

• Manufacturer Part Number: MAX8869
• Description: 1A, Microcap, Low-Dropout, Linear Regulator Foldback Output Current Limit
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 5. Power Operating Region: Maximum Output Current
vs. Input-Output Differential Voltage
to case) is the thermal resistance of the package cho-
sen, and θ
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
using a large pad (1in
multiple vias to the ground plane.
Capacitors are required at the MAX8869 input and out-
put. Connect 1µF or greater capacitors between IN and
GND (C
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
outputs), and connect C
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
IN
) and OUT and GND (C
CA
1.2
1.0
0.8
0.6
0.4
0.2
0
is the thermal resistance from the case
0
Applications Information
INPUT-OUTPUT DIFFERENTIAL VOLTAGE
_______________________________________________________________________________________
MAXIMUM CONTINUOUS CURRENT
1
T
T
A
A
= +70°C
= +50°C
T
2
Capacitor Selection and
IN
J
= +150°C
2
minimum recommended) or
and C
T
A
Regulator Stability
3
= +25°C
OUT
4
OUT
within 6mm of the
). Due to the
5
1A, Microcap, Low-Dropout,
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.
A capacitor (C
the MAX8869 output current to slowly rise during start-
up, reducing stress on the input supply. The rise time to
full current limit (t
where C
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.
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,
dropout voltage is the product of R
current (see
Voltage vs. Output Current in
Characteristics
remains low in dropout.
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-
cally 150µV
Typical Operating Characteristics) .
Noise, PSRR, and Transient Response
SS
is in nF. Typical capacitor values between
RMS.
Electrical Characteristics
Linear Regulator
SS
Input-Output (Dropout) Voltage
t
Soft-Start Capacitor Selection
SS
). The MAX8869 operating current
SS
) connected from SS to GND causes
(see the Output Noise plot in the
) is determined by:
= 2.08

10
-4

Typical Operating
C
SS
DS(ON
and Dropout
) and load
9