MIC5270
Micrel
MIC5270
IttyBitty™ Negative Low-Dropout Regulator
Preliminary Information
General Description
The MIC5270 is a
µCap
100mA negative regulator in a SOT-
23-5 package. With better than 2% initial accuracy, this
regulator provides a very accurate supply voltage for applica-
tions that require a negative rail. The MIC5270 sinks 100mA
of output current at very low dropout voltage (600mV maxi-
mum at 100mA of output current).
The
µCap
regulator design is optimized to work with low-
value, low-cost ceramic capacitors. The output typically re-
quires only a 1µF capacitance for stability.
Designed for applications where small packaging and effi-
ciency are critical, the MIC5270 combines LDO design exper-
tise with IttyBitty
™
packaging to improve performance and
reduce power dissipation. Ground current is optimized to help
improve battery life in portable applications.
The MIC5270 is available in the SOT-23-5 package for space
saving applications and it is available with fixed –3.0V, –4.1V,
and –5.0V outputs.
Features
•
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•
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IttyBitty
™
SOT-23-5 packaging
Low dropout voltage
Low ground current
Tight initial accuracy
Tight load and line regulation
Thermal shutdown
Current limiting
Stable with low-ESR ceramic capacitors
GaAsFET bias
Portable cameras and video recorders
PDAs
Battery-powered equipment
Applications
Ordering Information
Part Number
MIC5270-3.0BM5
MIC5270-4.1BM5
MIC5270-5.0BM5
Voltage
–3.0V
–4.1V
–5.0V
Temperature Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package
SOT-23-5
SOT-23-5
SOT-23-5
Typical Application
MIC5270-5.0
2
Pin Configuration
NC GND NC
3
4
2
1
V
IN
–6.0V
GND
–IN
–OUT
5
V
OUT
–5.0V
4
LLxx
5
1µF
10µF
–OUT
–IN
MIC5270-x.xBM5
Pin Description
Pin Number
1
2
3
4
5
Pin Name
NC
GND
NC
–OUT
–IN
Pin Function
Not internally connected.
Ground
Not internally connected.
Negative Regulator Output
Negative Supply Input
IttyBitty is a trademark of Micrel, Inc.
March 1999
283
MIC5270
MIC5270
Micrel
Absolute Maximum Ratings
(Note 1)
Input Voltage (V
–IN
) ....................................... –20V to +20V
Power Dissipation (P
D
) ............................ Internally Limited
Junction Temperature (T
J
) ....................... –40°C to +125°C
Lead Temperature (soldering, 5 sec.) ....................... 260°C
Storage Temperature (T
S
) ....................... –65°C to +150°C
ESD Rating,
Note 3
Operating Ratings
(Note 2)
Input Voltage (V
IN
) .......................................... –16V to –2V
Junction Temperature (T
J
) ....................... –40°C to +125°C
Thermal Resistance (θ
JA
).........................................
Note 4
Electrical Characteristics
V
IN
= V
OUT
– 1.0V; C
OUT
= 4.7µF, I
OUT
= 100µA; T
J
= 25°C,
bold
values indicate –40°C
≤
T
J
≤
+125°C; unless noted.
Symbol
V
OUT
∆V
OUT
/∆T
∆V
OUT
/V
OUT
∆V
OUT
/V
OUT
V
IN
– V
OUT
Parameter
Output Voltage Accuracy
Output Voltage Temperature
Coefficient
Line Regulation
Load Regulation
Dropout Voltage,
Note 7
Condition
Variation from nominal V
OUT
Note 5
V
IN
= V
OUT
– 1V to –16V
I
OUT
= 100µA to 100mA,
Note 6
I
OUT
= 100µA
I
OUT
= 10mA
I
OUT
= 50mA
I
OUT
= 100mA
I
GND
Ground Current,
Note 8
I
OUT
= 100µA
I
OUT
= 10mA
I
OUT
= 50mA
I
OUT
= 100mA
PSRR
I
LIMIT
∆V
OUT
/∆P
D
Note 1.
Note 2.
Note 3.
Note 4.
Min
–2
–3
Typ
Max
2
3
Units
%
%
ppm/°C
100
0.055
0.15
2.0
35
250
360
480
70
250
0.7
2.1
50
160
0.05
300
3.0
450
600
%/V
%
mV
mV
mV
mV
µA
µA
mA
mA
dB
mA
%/W
Ripple Rejection
Current Limit
Thermal Regulation
f = 120Hz
V
OUT
= 0V
Note 9
Exceeding the absolute maximum rating may damage the device.
The device is not guaranteed to function outside its operating rating.
Devices are ESD sensitive. Handling precautions recommended.
The maximum allowable power dissipation is a function of the maximum junction temperature, T
J(max)
, the junction-to-ambient thermal
resistance,
θ
JA
, and the ambient temperature, T
A
. The maximum allowable power dissipation at any ambient temperature is calculated using:
P
D(max)
= (T
J(max)
– T
A
)
÷ θ
JA
, where
θ
JA
is 235°C/W. Exceeding the maximum allowable power dissipation will result in excessive die
temperature, and the regulator will go into thermal shutdown. See the “Thermal Considerations” section for details.
Output voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
Regulation is measured at constant junction temperature using low duty cycle pulse testing. Parts are tested for load regulation in the load
range from 100µA to 100mA. Changes in output voltage due to heating effects are covered by the thermal regulation specification.
Dropout voltage is defined as the input to output differential at which the output voltage drops 2% below its nominal value measured at 1V
differential.
Ground pin current is the regulator quiescent current plus pass transistor base current. The total current drawn from the supply is the sum of
the load current plus the ground pin current.
Thermal regulation is defined as the change in output voltage at a time “t” after a change in power dissipation is applied, excluding load or line
regulation effects. Specifications are for a 100mA load pulse at V
IN
= –16V for t = 10ms.
Note 5.
Note 6.
Note 7.
Note 8.
Note 9.
MIC5270
284
March 1999
MIC5270
Micrel
Functional Diagram
GND
V
IN
MIC5270-x.x
V
OUT
March 1999
285
MIC5270
MIC5270
Micrel
Maximum power dissipation can be determined by knowing
the ambient temperature, T
A
, the maximum junction tem-
perature, 125°C, and the thermal resistance, junction to
ambient. The thermal resistance for this part, assuming a
minimum footprint board layout, is 235°C/W. The maximum
power dissipation at an ambient temperature of 25°C can be
determined with the following equation:
P
D(max)
=
P
D(max)
=
Applications Information
The MIC5270 is a general-purpose negative regulator that
can be used in any system that requires a clean negative
voltage from a negative output. This includes post regulating
of dc-dc converters (transformer based or charge pump
based voltage converters). These negative voltages typically
require a negative low-dropout voltage regulator to provide a
clean output from typically noisy lines.
Input Capacitor
A 1µF input capacitor should be placed from IN to GND if
there is more than 2 inches of wire or trace between the input
and the ac filter capacitor, or if a battery is used as the input.
Output Capacitor
The MIC5270 requires an output capacitor for stable opera-
tion. A minimum of 1µF of output capacitance is required. The
output capacitor can be increased without limitation to im-
prove transient response. The output does not require ESR
to maintain stability, therefore a ceramic capacitor can be
used. High-ESR capacitors may cause instability. Capacitors
with an ESR of 3Ω or greater at 100kHz may cause a high
frequency oscillation.
Low-ESR tantalums are recommended due to the tight ca-
pacitance tolerance over temperature.
Ceramic chip capacitors have a much greater dependence
on temperature, depending upon the dielectric. The X7R is
recommended for ceramic capacitors because the dielectric
will change capacitance value by approximately 15% over
temperature. The Z5U dielectric can change capacitance
value by as much 50% over temperature, and the Y5V
dielectric can change capacitance value by as much as 60%
over temperature. To use a ceramic chip capacitor with the
Y5V dielectric, the value must be much higher than a tanta-
lum to ensure the same minimum capacitor value over
temperature.
No-Load Stability
The MIC5270 does not require a load for stability.
Thermal Considerations
Absolute values will be used for thermal calculations to clarify
what is meant by power dissipation and voltage drops across
the part.
Proper thermal design for the MIC5270-5.0BM5 can be
accomplished with some basic design criteria and some
simple equations. The following information must be known
to implement your regulator design:
V
IN
= input voltage
V
OUT
= output voltage
I
OUT
= output current
T
A
= ambient operating temperature
I
GND
= ground current
T
J(max)
−
T
A
θ
JA
125
°
C
−
25
°
C
235
°
C/W
P
D(max)
=
425mW
The actual power dissipation of the regulator circuit can be
determined using one simple equation.
P
D
=
V
IN
−
V
OUT
I
OUT
+
V
IN
⋅
I
GND
Substituting P
D(max)
, determined above, for P
D
and solving
for the operating conditions that are critical to the application
will give the maximum operating conditions for the regulator
circuit. The maximum power dissipation number cannot be
exceeded for proper operation of the device. The maximum
input voltage can be determined using the output voltage of
5.0V and an output current of 100mA. Ground current, of 1mA
for 100mA of output current, can be taken from the Electrical
Characteristics section of the data sheet.
(
)
425mW
=
(
V
IN
−
5.0V
)
100mA
+
V
IN
⋅
1mA
425mW
=
(
100mA
⋅
V
IN
+
1mA
⋅
V
IN
)
−
500mW
925mW
=
101mA
⋅
V
IN
V
IN
=
9.16Vmax
Therefore, a –5.0V application at 100mA of output current
can accept a maximum input voltage of –9.16V in a SOT-23-5
package. For a full discussion of heat sinking and thermal
effects on voltage regulators, refer to Regulator Thermals
section of Micrel’s Designing with Low-Dropout Voltage Regu-
lators handbook.
MIC5270
286
March 1999
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