MIC5207-1.8BM5 Micrel Semiconductor, MIC5207-1.8BM5 Datasheet - Page 8

• Manufacturer Part Number: MIC5207-1.8BM5
• Description: 180mA Low-Noise LDO Regulator
• Manufacturer: Micrel Semiconductor

MIC5207
(see “Block Diagram”). Selecting larger output and bypass
capacitors allows additional time for the error amplifier and
reference to turn on and prevent overshoot.
To ensure that no overshoot is present when starting up into
a light load (100 A), use a 4.7 F 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 10 F
output capacitance and 470pF bypass capacitance. Lower
values of output and bypass capacitance can be used,
depending on the sensitivity of the system.
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.
Fixed Regulator Applications
Figure 1 includes a 470pF capacitor for ultra-low-noise op-
eration and shows EN (pin 3) connected to IN (pin 1) for an
application where enable/shutdown is not required. C
2.2 F minimum.
Figure 2 is an example of a basic low-noise configuration.
C
MIC5207
OUT
Figure 1. Ultra-Low-Noise Fixed Voltage Regulator
Figure 2. Low-Noise Fixed Voltage Regulator
= 1 F minimum.
100mA max.
Upstream
Shutdown
V
Enable
BUS
D+
GND
V
D–
BUS
V
V
IN
EN
IN
MIC5207-x.xBM5
MIC5207-x.xBM5
Data
1
2
3
1
2
3
1µF
MIC5207-3.3BZ
5
4
5
4
IN
470pF
GND
V
1.0µF
OUT
V
OUT
2.2µF
OUT
Figure 4. Single-Port Self-Powered Hub
1µF
USB Controller
OVERCURRENT
OUT
ON/OFF
=
8
Adjustable Regulator Applications
The MIC5207BM5 can be adjusted to a specific output
voltage by using two external resistors (figure 3). The resis-
tors set the output voltage based on the following equation:
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.
Resistor values are not critical because ADJ (adjust) has a
high input impedance, but for best results use resistors of
470k
greatly improved noise performance.
Figure 3 includes the optional 470pF noise bypass capacitor
from ADJ to GND to reduce output noise.
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 V
10 inches from the regulator, a 1 F input capacitor is in-
cluded.
V
OUT
or less. A capacitor from ADJ to ground provides
EN
FLG
GND
MIC2525
10k
Adjustable Voltage Regulator
V
REF
Figure 3. Ultra-Low-Noise
OUT
OUT
0.1µF
IN
IN
V
1
IN
5.0V
V
CC
R2
R1
150µF
MIC5207BM5
1
2
3
, V
BUS
470pF
Data
REF
Ferrite
Beads
supply may be greater than
5
4
1.242V
GND
V
R1
R2
BUS
D+
D–
V
2.2µF
USB
OUT
Port
January 2000
Micrel