MIC24046-H Datasheet, PDF(14/24 Page) Micrel Semiconductor – Pin-Programmable, 4.5V − 19V, 5A Step-Down Converter

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MIC24046-H Datasheet, PDF (14/24 Pages) Micrel Semiconductor – Pin-Programmable, 4.5V − 19V, 5A Step-Down Converter

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Micrel, Inc.

Setting the Output Voltage

The MIC24046-H output voltage can be programmed by

means of VOSET0, VOSET1 as shown in Table 2.

Table 2. Output Voltage Settings

VOSET1

VOSET0

0 (GND)

1 (VDDA)

0 (GND)

1 (VDDA)

0 (GND)

Hi-Z (Open)

Hi-Z (Open) 0 (GND)

1 (VDDA)

Hi-Z (Open)

Hi-Z (Open) 1 (VDDA)

Hi-Z (Open) Hi-Z (Open)

Output Voltage

3.3V

2.5V (2.49V)

1.8V

1.5V

1.2V

1.0V

0.9V

0.8V

0.7V

To achieve accurate output voltage regulation, the

OUTSNS pin (internal feedback divider top terminal) shall

be Kelvin-connected as close as possible to the point-of-

regulation top terminal. Also, since both the internal

reference and the internal feedback divider bottom

terminal are referred to AGND, it is important to minimize

voltage drops between the AGND and the point-of-

regulation return terminal.

Setting the Current Limit

The MIC24046-H valley-mode current limit on the low-

side MOSFET can be programmed by means of ILIM as

shown in Table 3.

Table 3. Current-Limit Setting

ILIM

Low-Side Valley

Current Limit

(Typical Value)

0 (GND)

4.6 A

1 (VDDA)

6.2 A

Hi-Z (Open)

6.8 A

Rated Output

Current

Note that the programmed current-limit values act as

pulse-by-pulse current-limit thresholds on the valley

inductor current. If the inductor current has not decayed

below the threshold at the time the PWM requires a new

ON time, the high-side MOSFET turn-on is either delayed

until the valley current recovers below the threshold or

skipped. Each time the high-side MOSFET turn-on is

skipped, a 4-bit up-down counter is incremented. When

the counter reaches the configuration 1111, a hiccup

sequence is invoked in order to reduce power dissipation

under prolonged short-circuit conditions.

The highest current-limit setting (6.8A) is intended to

comfortably accommodate a 5A application.

MIC24046-H

Ensure the maximum operating junction temperature is

not exceeded in high output power applications.

Inductor Selection

When selecting an inductor, it is important to consider the

following factors:

â¢ Inductance

â¢ Rated current value

â¢ Size requirements

â¢ DC resistance (DCR)

â¢ Core losses

The inductance value is critical to the operation of

MIC24046-H. Since the MIC24046-H is a valley current-

mode regulator, it needs slope compensation for stable

current loop operation at duty cycles below 50%. Slope

compensation is internally added according to the

frequency and output voltage selection, assuming a

minimum inductance value for the given operating

condition. According to this assumption, the minimum

inductor values recommended for stable current loop

operation are listed in Table 4. Note that the minimum

suggested inductance values should be met when taking

into account inductor tolerance and its change with bias

level.

Table 4. Recommended Inductance Values at VIN = 12V

VOUT

SELECTION

FREQUENCY

MINIMUM

INDUCTANCE

400kHz

0.97

0.7V, 0.8V, 0.9V,

565kHz

0.68

1.0V, 1.2V

790kHz

0.49

400kHz

1.51

1.5V, 1.8V

565kHz

1.06

790kHz

0.76

400kHz

2.42

2.49V, 3.3V

565kHz

1.70

790kHz

1.21

Slope compensation is also internally adapted to input

voltage, however higher inductance values than those

listed in Table 4 may be required to maintain current loop

stability, especially at the lower end of the input voltage

range (4.5V to 8V).

July 7, 2015

Revision 1.1

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