ADP3336 데이터 시트보기 (PDF) - Analog Devices
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ADP3336 Datasheet PDF : 9 Pages
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ADP3336
Output Voltage
The ADP3336 has an adjustable output voltage that can be set
by an external resistor divider. The output voltage will be
divided by R1 and R2, and then fed back to the FB pin.
In order to have the lowest possible sensitivity of the output
voltage to temperature variations, it is important that the paral-
lel resistance of R1 and R2 is always 50 kΩ.
R1× R2 = 50 kΩ
R1+ R2
Also, for the best accuracy over temperature the feedback volt-
age should be set for 1.178 V:
VFB
= VOUT
×
R2
R1+ R2
where VOUT is the desired output voltage and VFB is the “virtual
bandgap” voltage. Note that VFB does not actually appear at the
FB pin due to loading by the internal PTAT current.
Combining the above equations and solving for R1 and R2 gives
the following formulas:
R1 = 50 kΩ × VOUT
VFB
R2 = 50 kΩ
1
–
VFB
VOUT
VOUT
1.5 V
1.8 V
2.2 V
2.7 V
3.3 V
5V
10 V
Table I. Feedback Resistor Selection
R1 (1% Resistor)
63.4 kΩ
76.8 kΩ
93.1 kΩ
115 kΩ
140 kΩ
210 kΩ
422 kΩ
R2 (1% Resistor)
232 kΩ
147 kΩ
107 kΩ
88.7 kΩ
78.7 kΩ
64.9 kΩ
56.2 kΩ
Paddle-Under-Lead Package
The ADP3336 uses a proprietary paddle-under-lead package
design to ensure the best thermal performance in an MSOP-8
footprint. This new package uses an electrically isolated die
attach that allows all pins to contribute to heat conduction.
This technique reduces the thermal resistance to 110°C/W on a
4-layer board as compared to >160°C/W for a standard MSOP-8
leadframe. Figure 4 shows the standard physical construction
of the MSOP-8 and the paddle-under-lead leadframe.
DIE
Figure 4. Thermally Enhanced Paddle-Under-Lead Package
Thermal Overload Protection
The ADP3336 is protected against damage from excessive power
dissipation by its thermal overload protection circuit which limits
the die temperature to a maximum of 165°C. Under extreme
conditions (i.e., high ambient temperature and power dissipation)
where die temperature starts to rise above 165°C, the output
current is reduced until the die temperature has dropped to a
safe level. The output current is restored when the die tempera-
ture is reduced.
Current and thermal limit protections are intended to protect
the device against accidental overload conditions. For normal
operation, device power dissipation should be externally limited
so that junction temperatures will not exceed 150°C.
Calculating Junction Temperature
Device power dissipation is calculated as follows:
PD = (VIN – VOUT) ILOAD + (VIN) IGND
Where ILOAD and IGND are load current and ground current, VIN
and VOUT are input and output voltages respectively.
Assuming ILOAD = 400 mA, IGND = 4 mA, VIN = 5.0 V and
VOUT = 3.3 V, device power dissipation is:
PD = (5 – 3.3) 400 mA + 5.0(4 mA) = 700 mW
The proprietary package used in the ADP3336 has a thermal
resistance of 110°C/W, significantly lower than a standard
MSOP-8 package. Assuming a 4-layer board, the junction tem-
perature rise above ambient temperature will be approximately
equal to:
∆TJA = 0.700 W × 110°C = 77.0°C
To limit the maximum junction temperature to 150°C, maxi-
mum allowable ambient temperature will be:
TAMAX = 150°C – 77.0°C = 73.0°C
Printed Circuit Board Layout Consideration
All surface mount packages rely on the traces of the PC board to
conduct heat away from the package.
REV. A
–7–
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