MIC5163YMM Micrel Inc, MIC5163YMM Datasheet - Page 12

• Manufacturer Part Number: MIC5163YMM
• Description: IC REG CTLR DUAL MEM TERM 10MSOP
• Manufacturer: Micrel Inc

Specifications of MIC5163YMM

• Applications: Controller, DDR3, GDDR3/4/5
• Voltage - Input: 0.75 ~ 6 V
• Number Of Outputs: 1
• Voltage - Output: Programmable
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-3482-5

Where I_source is the average source current. Power
dissipation for the low-side MOSFET is as follows:
Where I_sink is the average sink current.
In a typical 3.5A peak DDR3 circuit, power considera-
tions for MOSFET selection would occur as follows.
This typical DDR3 application would require both high-
side and low-side N-Channel MOSFETs to be able to
handle 1.3125 Watts each. In applications where there is
excessive
MOSFETs may be placed in parallel. These MOSFETs
will share current, distributing power dissipation across
each device.
The maximum MOSFET die (junction) temperature limits
maximum power dissipation. The ability of the device to
dissipate heat away from the junction is specified by the
junction-to-ambient (θ
sum of junction-to-case (θ
to-sink (θ
(θ
In our example of a 3.5A peak DDR3 termination circuit,
we have selected a D-pack N-Channel MOSFET that
has a maximum junction temperature of 150°C. The
device has a junction-to-case thermal resistance of
1.5°C/W. Our application has a maximum ambient
temperature of 60°C. The required junction-to-ambient
thermal resistance can be calculated as follows:
Where T
maximum ambient temperature and P
dissipation.
In our example:
Micrel, Inc.
April 2009
SA
) thermal resistance;
P
P
P
P
P
θ
θ
θ
θ
J
JA
D
D
D
D
D
JA
JA
JA
is the maximum junction temperature, T
CS
= (V
= V
= (V
= (1.5V −0.75V) × 1.75A
= 1.3125 W
= θ
) thermal resistance and sink-to-ambient
power
=
=
=
T −
T −
TT
150
JC
DDQ
DDQ
J
J
. 1
× I_SINK
P
P
+ θ
D
D
°
3125
C
− V
−V
T
T
CS
A
A
dissipation,
−
TT
JA
TT
+ θ
60
W
) thermal resistance. This is the
) × I_SOURCE
) × I_SOURCE
°
SA
C
JC
) thermal resistance, case-
multiple
D
is the power
N-Channel
A
is the
12
This shows that our total thermal resistance must be
better
resistance is a combination of all the individual thermal
resistances, the amount of heat sink required can be
calculated as follows:
In our example:
In most cases, case-to-sink thermal resistance can be
assumed to be about 0.5°C/W.
The DDR3 termination circuit for our example, using 2 D-
pack N-Channel MOSFETs (one high side and one on
the low side) will require at least a 43°C/W heat sink per
MOSFET. This may be accomplished with an external
heat sink or even just the copper area that the MOSFET
is soldered to. In some cases, airflow may also be
required to reduce thermal resistance.
MOSFET Gate Threshold
N-Channel MOSFETs require an enhancement voltage
greater than its source voltage. Typical N-Channel
MOSFETs have a gate-source threshold (V
and higher. Since the source of the high side N-Channel
is connected to V
voltage equal to or greater than the V
example, our DDR3 termination circuit has a V
of 0.75V. For an N-Channel that has a V
2.5V, the V
N-Channel that has a 4.5V V
required is 5.25V. Although these N-Channels are driven
below
recommended that the V
to be able to fully enhance the MOSFETs for large signal
transient response. In addition, low gate thresholds
MOSFETs are recommended to reduce the V
requirements.
θ
θ
than
θ
θ
θ
their
SA
SA
SA
JA
SA
CC
= θ
= θ
=
=
=
68
66
voltage can be as low as 3.25V. With an
68
68.57°C/W.
JA
JA
full
.
.
.
− (θ
− (θ
57
57
57
TT
W
, the MIC5163 V
°
°
W
°
JC
JC
W
C
C
enhancement
C
+ θ
+ θ
−
CC
⎛
⎜
⎝
CS
CS
1
5 .
voltage has enough margin
Since
)
)
W
°
C
GS
+
, the minimum V
0
5 .
the
threshold,
CC
°
W
M9999-042209-A
C
GS
pin requires a
⎞
⎟
⎠
total
voltage. For
GS
GS
MIC5163
TT
) of 1.8V
rating of
thermal
voltage
it
CC
CC
is