Micrel, Inc.
VIN(MAX) = 6.01V
MIC5207
Therefore, a 3.3V application at 150mA of output current
can accept a maximum input voltage of 6V in a SOT-23-
5 package. For a full discussion of heat sinking and
thermal effects on voltage regulators, refer to the
Regulator Thermals section of Micrel’s Designing with
Low-Dropout Voltage Regulators handbook
Figure 2. Low-Noise Fixed Voltage Application
Low-Voltage Operation
Figure
2
is an example of
a
basic low-noise
The MIC5207-1.8 and MIC5207-2.5 require special
consideration when used in voltage-sensitive systems.
They may momentarily overshoot their nominal output
voltages unless appropriate output and bypass capacitor
values are chosen.
configuration. COUT = 1µF minimum.
Adjustable Regulator Applications
The MIC5207BM5 can be adjusted to a specific output
voltage by using two external resistors (Figure 3). The
resistors set the output voltage based on the following
equation:
During regulator power up, the pass transistor is fully
saturated for a short time, while the error amplifier and
voltage reference are being powered up more slowly
from the output (see “Block Diagram”). Selecting larger
output and bypass capacitors allows additional time for
the error amplifier and reference to turn on and prevent
overshoot.
R2
R1
⎛
⎞
VOUT = VREF 1+
, V
= 1.242V
⎜
⎟
REF
⎝
⎠
This equation is correct due to the configuration of the
bandgap reference. The bandgap voltage is relative to
the output, as seen in the block diagram. Traditional
regulators normally have the reference voltage relative
to ground; therefore, their equations are different from
the equation for the MIC5207BM5.
To ensure that no overshoot is present when starting up
into a light load (100µA), use a 4.7µF output capacitance
and 470pF bypass capacitance. This slows the turn-on
enough to allow the regulator to react and keep the
output voltage from exceeding its nominal value. At
heavier loads, use a 10µF output capacitance and
470pF bypass capacitance. Lower values of output and
bypass capacitance can be used, depending on the
sensitivity of the system.
Resistor values are not critical because ADJ (adjust) has
a high input impedance, but for best results use resistors
of 470kΩ or less. A capacitor from ADJ to ground
provides greatly improved noise performance.
Applications that can withstand some overshoot on the
output of the regulator can reduce the output capacitor
and/or reduce or eliminate the bypass capacitor.
Applications that are not sensitive to overshoot due to
power-on reset delays can use normal output and
bypass capacitor configurations.
Please note the junction temperature range of the
regulator at 1.8V output (fixed and adjustable) is 0˚C to
+125˚C.
Figure 3. Ultra-Low-Noise Adjustable Voltage Application
Figure 3 includes the optional 470pF noise bypass
capacitor from ADJ to GND to reduce output noise.
Fixed Regulator Applications
Dual-Supply Operation
When used in dual-supply systems where the regulator
load is returned to a negative supply, the output voltage
must be diode clamped to ground.
USB Application
Figure 4 shows the MIC5207-3.3BZ (3-terminal, TO-92)
in a USB application. Since the VBUS supply may be
greater than 10 inches from the regulator, a 1µF input
capacitor is included.
Figure 1. Ultra-Low-Noise Fixed Voltage Application
Figure 1 includes a 470pF capacitor for ultra-low-noise
operation and shows EN (pin 3) connected to IN (pin 1)
for an application where enable/shutdown is not
required. COUT = 2.2µF minimum.
M9999-123107
December 2007
10
MICREL [ MICREL SEMICONDUCTOR ]
