M
Applications Information
Capacitor Selection
and Regulator Stability
Use a 2.2μF capacitor on the MAX8530/MAX8531s
’
inputs. Larger input capacitor values with lower ESRs
provide better supply-noise rejection and line-transient
response. To reduce noise and improve load transients,
use large-output capacitors, up to 10μF. For stable
operation over the full temperature range and with rated
maximum load currents, use a minimum of 2.2μF (or
1μF for <150mA loading for OUT1) and 1μF for OUT2.
Note that some ceramic dielectrics exhibit large capac-
itance and ESR variation with temperature. With
dielectrics such as Z5U and Y5V, it is necessary to use
4.7μF or more to ensure stability at temperatures below
-10
°
C. With X7R or X5R dielectrics, 2.2μF is sufficient at
all operating temperatures. These regulators are opti-
mized for ceramic capacitors. Tantalum capacitors are
not recommended.
PSRR and Operation from
Sources Other than Batteries
The MAX8530/MAX8531 is designed to deliver low
dropout voltages and low quiescent currents in battery-
powered systems. Power-supply rejection is 60dB at
low frequencies (see the Power-Supply Rejection Ratio
vs. Frequency graph in the
Typical Operating Char-
acteristics
).
When operating from sources other than batteries,
improve supply-noise rejection and transient response
by increasing the values of the input and output bypass
capacitors and through passive filtering techniques.
Load-Transient Considerations
The MAX8530/MAX8531 load-transient response
graphs (see the
Typical Operating Characteristics
)
show two components of the output response: a DC
shift in the output voltage because of the different load
currents, and the transient response. Increase the output
capacitor
’
s value and decrease its ESR to attenuate
transient spikes.
Input/Output (Dropout Voltage)
A regulator
’
s minimum input/output voltage differential
(or dropout voltage) determines the lowest usable supply
voltage. In battery-powered systems, this determines
the useful end-of-life battery voltage. Because the
MAX8530/MAX8531 use a P-channel MOSFET pass
transistor, their dropout voltage is a function of drain-to-
source on-resistance (R
DS(ON)
) multiplied by the load
current (see the
Typical Operating Characteristics
).
Calculating the Maximum
Output Power in UCSP
The maximum output power of the MAX8530/MAX8531
can be limited by the maximum power dissipation of the
package. Obtain the maximum power dissipation by
calculating the power dissipation of the package as a
function of the input voltage, output voltage, and output
currents. The maximum power dissipation should not
exceed the package
’
s maximum power rating:
P = (V
IN(MAX)
- V
OUT1
) x I
OUT1
+
(V
IN(MAX)
- V
OUT2
) x I
OUT2
where:
V
IN(MAX)
= Maximum input voltage
P
MAX
= Maximum power dissipation of the package
(308mW for UCSP and 1951mW for the QFN package)
V
OUT1
= Output voltage of OUT1
V
OUT2
= Output voltage of OUT2
I
OUT1
= Maximum output current of OUT1
I
OUT2
= Maximum output current of OUT2
P should be less than P
MAX
. If P is greater than P
MAX
,
consider using the QFN package.
Dual Low-Dropout Linear Regulators
with
RESET
or Low-Noise Output in UCSP or QFN
8
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