MIC5211-1.8/2.5BM6 MICREL [Micrel Semiconductor], MIC5211-1.8/2.5BM6 Datasheet - Page 7

• Manufacturer Part Number: MIC5211-1.8/2.5BM6
• Description: Dual ?Cap 80mA LDO Regulator Preliminary Information
• Manufacturer: MICREL [Micrel Semiconductor]

MIC5211
Applications Information
Enable/Shutdown
ENA and ENB (enable/shutdown) may be controlled sepa-
rately. Forcing ENA/B high (>2V) enables the regulator. The
enable inputs typically draw only 15 A.
While the logic threshold is TTL/CMOS compatible, ENA/B
may be forced as high as 20V, independent of V
may be connected to the supply if the function is not required.
Input Capacitor
A 0.1 F capacitor should be placed from IN to GND if there
is more than 10 inches of wire between the input and the ac
filter capacitor or when a battery is used as the input.
Output Capacitor
Typical PNP based regulators require an output capacitor to
prevent oscillation. The MIC5211 is ultrastable, requiring only
0.1 F of output capacitance per regulator for stability. The
regulator is stable with all types of capacitors, including the
tiny, low-ESR ceramic chip capacitors. The output capacitor
value can be increased without limit to improve transient
response.
The capacitor should have a resonant frequency above
500kHz. Ceramic capacitors work, but some dielectrics have
poor temperature coefficients, which will affect the value of
the output capacitor over temperature. Tantalum capacitors
are much more stable over temperature, but typically are
larger and more expensive. Aluminum electrolytic capacitors
will also work, but they have electrolytes that freeze at about
–30 C. Tantalum or ceramic capacitors are recommended
for operation below –25 C.
No-Load Stability
The MIC5211 will remain stable and in regulation with no load
(other than the internal voltage divider) unlike many other
voltage regulators. This is especially important in CMOS
RAM keep-alive applications.
Thermal Shutdown
Thermal shutdown is independent on both halves of the dual
MIC5211, however, an overtemperature condition in one half
may affect the other half because of proximity.
Thermal Considerations
When designing with a dual low-dropout regulator, both
sections must be considered for proper operation. The part is
designed with thermal shutdown, therefore, the maximum
junction temperature must not be exceeded. Since the dual
regulators share the same substrate, the total power dissipa-
tion must be considered to avoid thermal shutdown. Simple
thermal calculations based on the power dissipation of both
regulators will allow the user to determine the conditions for
proper operation.
The maximum power dissipation for the total regulator sys-
tem can be determined using the operating temperatures and
the thermal resistance of the package. In a minimum footprint
configuration, the SOT-23-6 junction-to-ambient thermal re-
sistance
temperature for this device is 125 C, at an operating tem-
perature of 25 C the maximum power dissipation is:
November 2000
JA
) is 220 C/W. Since the maximum junction
IN
. ENA/B
7
The MIC5211-3.0 can supply 3V to two different loads inde-
pendently from the same supply voltage. If one of the regu-
lators is supplying 50mA at 3V from an input voltage of 4V, the
total power dissipation in this portion of the regulator is:
Up to approximately 400mW can be dissipated by the remain-
ing regulator (455mW – 53.4mW) before reaching the ther-
mal shutdown temperature, allowing up to 50mA of current.
The total power dissipation is:
Therefore, with a supply voltage of 4V, both outputs can
operate safely at room temperature and full load (50mA).
In many applications, the ambient temperature is much
higher. By recalculating the maximum power dissipation at
70 C ambient, it can be determined if both outputs can supply
full load when powered by a 4V supply.
At 70 C, the device can provide 250mW of power dissipation,
suitable for the above application.
When using supply voltages higher than 4V, do not exceed
the maximum power dissipation for the device. If the device
P
P
P
P
P
P
P
P
P
P
P
P
P
P
D(max)
D(max)
D(max)
D1
D1
D1
D2
D2
D2
D1
D1
D(max)
D(max)
D(max)
V
Figure 1. Thermal Conditions Circuit
IN
P
P
53.4mW
53.4mW
V
4V 3V 50mA 4V 0.85mA
D2
D2
V
4V 3V 50mA 4V 0.85mA
IN
IN
ENA OUTB
ENB
IN
MIC5211
125 C 25 C
455mW
125 C 70 C
250mW
T
T
J(max)
J(max)
106.8mW
53.4mW 53.4mW
V
220 C/W
220 C/W
V
OUT OUT
OUTA
OUT OUT
GND
JA
JA
I
I
T
T
A
A
V
V
IN GND
IN GND
1µF
I
I
1µF
V
V
OUTA
OUTB
MIC5211
Micrel