MIC2829 datasheet(35/52 Pages) MICREL

35 / 52 page

Micrel Inc.

MIC2829

May 2010

M9999-051410-B

becomes increasingly critical in efficiency calculations.

As the inductors are reduced in size, the DC resistance

(DCR) can become quite significant. The DCR losses

can be calculated as follows:

PL_LOSS ≈ IOUT

2 × DCR

From that, the loss in efficiency due to inductor

resistance can be calculated as follows:

100

⎥

⎦

⎤

⎢

⎣

⎡

⎟

⎠

⎞

⎜

⎝

⎛

−

≈

LOSS

OUT

Loss

Efficiency

Efficiency loss due to DCR is minimal at light loads and

gains significance as the load is increased. Inductor

selection becomes a trade-off between efficiency and

size in this case.

Partitioning for Optimal System Efficiency

Many of the LDOs can be post-regulated from the DC

regulator output to increase system efficiency. For

example, DC4 output can be used to power low output

voltage LNRs in order to reduce power loss during

voltage conversion.

Thermal Considerations

Whenever there is power dissipation, there will be

thermal considerations. In order to account for the

temperature rise in a PMIC with multiple regulators, the

power dissipation in each regulator must be accounted

for. The current rating of each regulator is shown below:

Output

Maximum Load (mA)

DC1

1000

DC2

300

DC3

600

DC4

600

DC5

800

DC6

800

LDO1

200

LDO2

200

LDO3

200

LDO4

200

LDO5

200

LDO6

200

LDO7

200

LDO8

200

LDO9

200

LDO10

200

LDO11

200

SIMPWR

Table 5. Output Current Rating

If each regulator on the MIC2829 is turned on at its

maximum load capability, the power dissipation into the

device will cause excessive temperature rise. In order to

avoid excessive temperature rise and unexpected

thermal shutdown the total power dissipation should be

considered.

LDO Power Dissipation

The power dissipation of a LDO can be calculated with

the input voltage, the output voltage and the output

current, as shown in the following equation.

PD_LDO ≈ (VIN – VOUT) IOUT + VIN IGND

Since the ground current (IGND) is relatively low, it can be

ignored for this calculation. For example, if the input

voltage is 3.3V, the output voltage is 2.8V and the output

current of the LDO is 200mA, the power dissipation of the

LDO can be calculated as follow:

PD_LDO ≈ (3.3V – 2.8V) × 200mA

PD_LDO ≈ 0.1W

Buck Regulator Power Dissipation

Neglecting some minor losses, the power dissipation in a

MIC2829 buck regulator (DC1 to DC6) is approximately

the switcher’s input power minus the switcher’s output

power and minus the power loss in the inductor.

PD_SWITCHER ≈ PIN x IIN – POUT x IOUT – PL_LOSS

Total Power Dissipation

The total power dissipation in the MIC2829 package is

equal to the sum of the power loss of each regulator.

PD_TOTAL ≈ SUM (PD_LDOS + PD_SWITCHERS)

The maximum power dissipation of the package can be

calculated by the following equation.

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

≈

)

max

TJ(MAX) is the maximum junction temperature (125°C), TA

is the ambient temperature and

JA is the junction-to-

ambient thermal resistance of the package (38.7°C/W).

The following table shows

the

maximum

power

dissipation versus the ambient temperature.

MIC2829 数据表(PDF) 35 Page - Micrel Semiconductor

MIC2829 数据表(HTML) 35 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52

数据表下载