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MIC5270
Micrel
MIC5270
IttyBittyTM Negative Low-Dropout Regulator Preliminary Information
General Description
The MIC5270 is a Cap 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 Cap regulator design is optimized to work with lowvalue, low-cost ceramic capacitors. The output typically requires only a 1F capacitance for stability. Designed for applications where small packaging and efficiency are critical, the MIC5270 combines LDO design expertise with IttyBittyTM 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.
Part Number MIC5270-3.0BM5 MIC5270-4.1BM5 MIC5270-5.0BM5
Features
* * * * * * * * * * * * IttyBittyTM 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
Voltage -3.0V -4.1V -5.0V Temperature Range -40C to +85C -40C to +85C -40C to +85C 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
VIN -6.0V
GND -IN -OUT
5
VOUT -5.0V
4
LLxx
5
1F
10F
-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 (PD) ............................ Internally Limited Junction Temperature (TJ) ....................... -40C to +125C Lead Temperature (soldering, 5 sec.) ....................... 260C Storage Temperature (TS) ....................... -65C to +150C ESD Rating, Note 3
Operating Ratings (Note 2)
Input Voltage (VIN) .......................................... -16V to -2V Junction Temperature (TJ) ....................... -40C to +125C Thermal Resistance (JA)......................................... Note 4
Electrical Characteristics
VIN = VOUT - 1.0V; COUT = 4.7F, IOUT = 100A; TJ = 25C, bold values indicate -40C TJ +125C; unless noted. Symbol VOUT VOUT/T VOUT/VOUT VOUT/VOUT VIN - VOUT Parameter Output Voltage Accuracy Output Voltage Temperature Coefficient Line Regulation Load Regulation Dropout Voltage, Note 7 Condition Variation from nominal VOUT Note 5 VIN = VOUT - 1V to -16V IOUT = 100A to 100mA, Note 6 IOUT = 100A IOUT = 10mA IOUT = 50mA IOUT = 100mA IGND Ground Current, Note 8 IOUT = 100A IOUT = 10mA IOUT = 50mA IOUT = 100mA PSRR ILIMIT VOUT/PD
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 A A mA mA dB mA %/W
Ripple Rejection Current Limit Thermal Regulation
f = 120Hz VOUT = 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, TJ(max), the junction-to-ambient thermal resistance, JA, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated using: PD(max) = (TJ(max) - TA) / JA, where JA is 235C/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 100A 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 VIN = -16V for t = 10ms.
Note 5. Note 6. Note 7. Note 8. Note 9.
MIC5270
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March 1999
MIC5270
Micrel
Functional Diagram
GND
VIN MIC5270-x.x
VOUT
March 1999
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MIC5270
MIC5270
Micrel
Maximum power dissipation can be determined by knowing the ambient temperature, TA, the maximum junction temperature, 125C, and the thermal resistance, junction to ambient. The thermal resistance for this part, assuming a minimum footprint board layout, is 235C/W. The maximum power dissipation at an ambient temperature of 25C can be determined with the following equation:
PD(max) =
PD(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 1F 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 1F 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 3 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
TJ(max) - TA JA
125C - 25C 235C/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.
MIC5270
286
March 1999

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