MIC5191 Datasheet, PDF(6/13 Page) Micrel Semiconductor – Ultra High-Speed, High-Current Active Filter/LDO Controller

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MIC5191 Datasheet, PDF (6/13 Pages) Micrel Semiconductor – Ultra High-Speed, High-Current Active Filter/LDO Controller

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MIC5191

Functional Diagram

Micrel

VCC1

INTERNAL

VOLTAGE

REGULATOR

VIN

50mV

ENABLE

CURRENT LIMIT

AMPLIFIER

OUTPUT

CONTROL

AND

LEVEL

SHIFT

VCC2

OUT

PGND

COMP

ERROR 1V

AMPLIFIER

SGND

Figure 1. MIC5191 Block Diagram

Functional Description

VIN

The VIN pin is connected to the N-Channel drain. VIN is the

input power being supplied to the output. This pin is also used

to power the internal current limit comparator and compare

the ISENSE voltage for current limit. The voltage range is

from 1.0V min to 5.5V max.

ISENSE

The ISENSE pin is the other input to the current limit com-

parator. The output current is limited when the ISENSE pin's

voltage is 50mV less than the VIN pin. In cases where there

is a current limited source and there isnât a need for current

limit, this pin can be tied directly to VIN. Its operating voltage

range, like the VIN pin, is 1.0V min to 5.5V max.

VCC1, VCC2

VCC1 supplies the error amplifier and internal reference,

while VCC2 supplies the output gate drive. For this reason,

ensure these pins have good input capacitor bypassing for

better performance. The operating range is from 4.5V to

13.2V and both VCC pins should be tied together. Ensure that

the voltage supplied is greater than a gate-source threshold

above the output voltage for the N-Channel MOSFET se-

lected.

Output

The output drives the external N-Channel MOSFET and is

powered from VCC. The output can sink and source over

150mA of current to drive either an N-Channel MOSFET or an

external NPN transistor. The output drive also has short-

circuit current protection.

Enable

The MIC5191 comes with an active-high enable pin that

allows the regulator to be disabled. Forcing the enable pin low

disables the regulator and sends it into a low off-mode-

current state. Forcing the enable pin high enables the output

voltage. The enable pin cannot be left floating; a floating

enable pin may cause an indeterminate state on the output.

The feedback pin is used to sense the output voltage for

regulation. The feedback pin is compared to an internal 1.0V

reference and the output adjusts the gate voltage accordingly

to maintain regulation. Since the feedback biasing current is

typically 13ÂµA, smaller feedback resistors should be used to

minimize output voltage error.

COMP

COMP is the external compensation pin. This allows com-

plete control over the loop to allow stability for any type of

output capacitor, load currents and output voltage. A detailed

explanation of how to compensate the MIC5191 is in the

âDesigning with the MIC5191â section.

SGND, PGND

SGND is the internal signal ground which provides an iso-

lated ground path from the high current output driver. The

signal ground provides the grounding for noise sensitive

circuits such as the current limit comparator, error amplifier

and the internal reference voltage.

PGND is the power ground and is the grounding path for the

output driver.

April 2004

M9999-042804

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