MIC61300 datasheet(12/22 Pages) MICREL

12 / 22 page

Micrel, Inc.

MIC61300

September 2010

M9999-092910-A

Functional Description

The MIC61300 is an ultra-high-performance, low-dropout

linear regulator designed for high-current applications

that require low input voltage operation. The MIC61300

operates from a single input supply and generates an

internal supply that is higher than the input voltage to

drive an on-chip N-Channel MOSFET. The N-Channel

MOSFET significantly reduces the dropout voltage when

compared to a traditional P-Channel MOSFET.

P-Channel MOSFETs are usually used in single-supply

low-dropout linear voltage regulators. However, for input

voltages below 1.5V, there is not sufficient gate drive to

turn on the P-Channel. To solve this issue, the

MIC61300 uses a simple internal charge pump to drive

the internal N-Channel MOSFET’s gate higher than the

input voltage, see Functional Diagram. The N-Channel

MOSFET greatly reduces the dropout voltage for the

same die area when compared to that of a P-Channel.

Other added benefits of the charge pump include the

ability to control the output voltage rise time and to

improve the power supply rejection ratio (PSRR). This is

accomplished by using the VCP supply to power the error

amplifier.

The other significant advantage of the MIC61300 over a

P-Channel regulator is its transient response. The N-

Channel in the follower configuration is much faster than

its P-channel counter part and is simpler to compensate.

Any type of output capacitor can be placed in parallel

with it as long as the minimum value output ceramic

capacitor is placed next to the MIC61300. See the

Output Capacitor

section for specific details. Also, the

regulator is fully protected from damage due to fault

conditions by offering linear current limiting and thermal

shutdown.

Soft-Start

Soft-start reduces the power supply input surge current

at startup by controlling the output voltage rise time. The

input surge appears while the output capacitor is

charged up. A slower output rise time will draw a lower

input surge current.

The CP pin is the output of the internal charge pump.

The soft-start rise time is controlled by the external

capacitor connected from CP pin-to-GND. During soft-

start, the charge pump feeds a current to CCP. The

output voltage rise time is dependent upon the value of

CCP, the input voltage, output voltage and the current

limit. The value of the charge pump external capacitor

selected is recommended in the range of 0.1µF to 1µF.

Input Capacitor

A 10µF ceramic input capacitor is all that is required for

most applications. However, fast load transient and low

headroom (VIN – VOUT) requires additional bulk bypass

capacitance to ensure that the regulator does not drop

out of regulation.

The input capacitor must be placed on the same side of

the board and next to the MIC61300 to minimize the

dropout voltage and voltage ringing during transient and

short circuit conditions. It is also recommended to use

two vias for each end of the capacitor to connect to the

power and ground plane.

X7R

X5R

dielectric

ceramic

capacitors

are

recommended

because

their

temperature

performance. X7R-type capacitors change capacitance

by 15% over their operating temperature range and are

the most stable type of ceramic capacitors. Z5U and

Y5V dielectric capacitors change value by as much as

50% and 60% respectively over their operating

temperature ranges. To use a ceramic chip capacitor

with Y5V dielectric, the value must be much higher than

an X7R ceramic or a tantalum capacitor to ensure the

same capacitance value over the operating temperature

range. Tantalum capacitors have a very stable dielectric

(10% over their operating temperature range) and can

also be used in parallel with the ceramic capacitor(s).

See Typical Characteristics section for examples of load

transient response.

Output Capacitor

As part of the frequency compensation, the MIC61300

requires a 47µF ceramic output capacitor. However, any

other type of capacitor can be placed in parallel as long

as the 47µF ceramic output capacitor is placed next to

the MIC61300.

Output voltages below 0.8V require either a 100µF or

2x 47µF output capacitance for large output transients.

The increased output capacitance reduces the output

voltage drop caused by load transients, which increases

as a percentage of the output voltage as the output

voltage is lowered.

The output capacitor type and placement criteria are the

same as the input capacitor. See the Input Capacitor

section for a detailed description.

Minimum Load Current

The MIC61300 requires a minimum load of 10mA to

maintain output voltage regulation.

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