MIC5271 datasheet(10/20 Pages) MICROCHIP

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MIC5271

DS20005881B-page 10



2017 - 2022 Microchip Technology Inc. and its subsidiaries

4.0

APPLICATION INFORMATION

The MIC5271 is a general-purpose negative voltage

regulator that can be used in a system that requires a

clean negative voltage. This includes the post

regulation of DC/DC converters (transformer or charge

pump based voltage converters). These negative

voltages typically require a negative low dropout

voltage regulator to provide a clean output from noisy

input power.

4.1

Input Capacitor

A 1 µF input capacitor should be placed from –IN to

GND if there is more than two inches of wire or trace

between the input and the AC filter capacitor or if a

battery is used as the input.

4.2

Output Capacitor

The MIC5271 requires an output capacitor for stable

operation. A minimum of 1 µF 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 100 kHz can cause a

high-frequency oscillation.

Low-ESR tantalums are recommended due to the tight

capacitance tolerance 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.

4.3

No-Load Stability

The MIC5271 does not require a load for stability.

4.4

Enable Input

The MIC5271 comes with an enable pin that allows the

regulator to be disabled. Forcing the enable pin higher

than the negative threshold and lower than the positive

threshold disables the regulator and sends it into a

“zero” off-mode current state. In this state, current

consumed by the regulator goes nearly to zero,

typically drawing only ±1 µA. The MIC5271 will be in

the “on” mode when the voltage applied to the enable

pin is either greater than the positive threshold or less

than the negative threshold.

FIGURE 4-1:

Positive and Negative

Enable Voltage vs. Supply Voltage.

4.5

Thermal Considerations

Absolute values will be used for thermal calculations to

clarify the meaning of power dissipation and voltage

drops across the part.

Proper thermal design for the MIC5271-5.0YM5 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

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 Equation 4-1 and Equation 4-2:

–1

–2

–3

–4

–5

–7

–15

–3

–13

–11

–9

ENABLE INPUT

REGULATOR ON

REGULATOR OFF

REGULATOR ON

SUPPLY VOLTAGE (V)

–5

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