MICREL MIC5270

MIC5270
Micrel
MIC5270
IttyBitty™ Negative Low-Dropout Regulator
Preliminary Information
General Description
Features
The MIC5270 is a µCap 100mA negative regulator in a SOT23-5 package. With better than 2% initial accuracy, this
regulator provides a very accurate supply voltage for applications that require a negative rail. The MIC5270 sinks 100mA
of output current at very low dropout voltage (600mV maximum at 100mA of output current).
The µCap regulator design is optimized to work with lowvalue, low-cost ceramic capacitors. The output typically requires only a 1µF capacitance for stability.
Designed for applications where small packaging and efficiency are critical, the MIC5270 combines LDO design expertise 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.
•
•
•
•
•
•
•
•
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
Applications
•
•
•
•
GaAsFET bias
Portable cameras and video recorders
PDAs
Battery-powered equipment
Ordering Information
Part Number
Voltage
Temperature Range
Package
MIC5270-3.0BM5
–3.0V
–40°C to +85°C
SOT-23-5
MIC5270-4.1BM5
–4.1V
–40°C to +85°C
SOT-23-5
MIC5270-5.0BM5
–5.0V
–40°C to +85°C
SOT-23-5
Typical Application
Pin Configuration
NC GND NC
MIC5270-5.0
2
VIN
–6.0V
5
3
GND
–IN
1µF
–OUT
4
VOUT
–5.0V
2
1
LLxx
10µF
4
5
–OUT
–IN
MIC5270-x.xBM5
Pin Description
Pin Number
Pin Name
1
NC
2
GND
3
NC
4
–OUT
5
–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)
Operating Ratings (Note 2)
Input Voltage (V–IN) ....................................... –20V to +20V
Power Dissipation (PD) ............................ Internally Limited
Junction Temperature (TJ) ....................... –40°C to +125°C
Lead Temperature (soldering, 5 sec.) ....................... 260°C
Storage Temperature (TS) ....................... –65°C to +150°C
ESD Rating, Note 3
Input Voltage (VIN) .......................................... –16V to –2V
Junction Temperature (TJ) ....................... –40°C to +125°C
Thermal Resistance (θJA)......................................... Note 4
Electrical Characteristics
VIN = VOUT – 1.0V; COUT = 4.7µF, IOUT = 100µA; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ +125°C; unless noted.
Symbol
Parameter
Condition
VOUT
Output Voltage Accuracy
Variation from nominal VOUT
∆VOUT/∆T
Output Voltage Temperature
Coefficient
Note 5
∆VOUT/VOUT
Line Regulation
VIN = VOUT – 1V to –16V
∆VOUT/VOUT
Load Regulation
IOUT = 100µA to 100mA, Note 6
VIN – VOUT
Dropout Voltage, Note 7
IOUT = 100µA
35
mV
IOUT = 10mA
250
mV
IOUT = 50mA
360
450
mV
IOUT = 100mA
480
600
mV
IOUT = 100µA
70
µA
IOUT = 10mA
250
µA
IOUT = 50mA
0.7
mA
IOUT = 100mA
2.1
IGND
Ground Current, Note 8
Min
Typ
–2
–3
Max
Units
2
3
%
%
100
0.055
PSRR
Ripple Rejection
f = 120Hz
50
ILIMIT
Current Limit
VOUT = 0V
160
∆VOUT/∆PD
Thermal Regulation
Note 9
0.05
ppm/°C
0.15
%/V
2.0
%
3.0
mA
dB
300
mA
%/W
Note 1.
Exceeding the absolute maximum rating may damage the device.
Note 2.
The device is not guaranteed to function outside its operating rating.
Note 3.
Devices are ESD sensitive. Handling precautions recommended.
Note 4.
The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(max), the junction-to-ambient thermal
resistance, θJA, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated using:
PD(max) = (TJ(max) – TA) ÷ θJA, where θJA 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.
Note 5.
Output voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
Note 6.
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.
Note 7.
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.
Note 8.
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.
Note 9.
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 VIN = –16V for t = 10ms.
MIC5270
284
March 1999
MIC5270
Micrel
Functional Diagram
GND
VIN
VOUT
MIC5270-x.x
March 1999
285
MIC5270
MIC5270
Micrel
Maximum power dissipation can be determined by knowing
the ambient temperature, TA, the maximum junction temperature, 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:
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 operation. A minimum of 1µF of output capacitance is required. The
output capacitor can be increased without limitation to improve 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 capacitance 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 tantalum 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:
VIN = input voltage
VOUT = output voltage
IOUT = output current
TA = ambient operating temperature
IGND = ground current
MIC5270
PD(max) =
PD(max) =
TJ(max) − TA
θ JA
125°C − 25°C
235°C/W
PD(max) = 425mW
The actual power dissipation of the regulator circuit can be
determined using one simple equation.
(
)
PD = VIN − VOUT IOUT + VIN ⋅ IGND
Substituting PD(max), determined above, for PD 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 = (VIN − 5.0V) 100mA + VIN ⋅ 1mA
425mW = (100mA ⋅ VIN + 1mA ⋅ VIN ) − 500mW
925mW = 101mA ⋅ VIN
VIN = 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 Regulators handbook.
286
March 1999