EUP7907A
Application Information
The maximum power dissipation depends on the thermal
resistance of IC package, PCB layout, the rate of
surroundings airflow and temperature difference between
junction to ambient. The maximum power dissipation can
be calculated by following formula :
External Capacitor
Like other low-dropout regulator, the EUP7907A
requires external capacitors for stability. It is specifically
designed for low-ESR capacitors requiring minimum
PCB area and smallest components.
PD(MAX) = (TJ(MAX) − TA ) θJA
Where TJ(MAX) is the maximum operation junction
temperature 125°C, TA is the ambient temperature and the
θJA is the junction to ambient thermal resistance.
(EQ.4)
Input Capacitor
A 2.2uF capacitor is required between the VIN pin and
the GND pin. Place it as close as possible to the device.
There are no requirements for the ESR on the input
capacitor, but the tolerance and temperature coefficient
must be considered when selecting the capacitor to
ensure the capacitance will be 2.2uF over the whole
operating temperature range.
For recommended operating conditions specification of
EUP7907A, where TJ(MAX) is the maximum junction
temperature of the die (125°C) and TA is the operated
ambient temperature. The junction to ambient thermal
resistance θJA is layout dependent. For SOT-23-5 package,
the thermal resistance θJA is 220°C/W on the standard
thermal test board. For TDFN-6 package, the thermal
resistance θJA is 90°C/W on the standard thermal test
board. The maximum power dissipation at TA = 25°C can
be calculated by following formula :
Output Capacitor
The EUP7907A is designed specifically to work with
very small ceramic output capacitors. A 2.2uF to 10uF
with 5mΩ to 500mΩ ESR range is suitable in the
EUP7907A application circuit. The ESR of a typical
2.2uF ceramic capacitor is about 20mΩ, which easily
meets the ESR requirement for stability.
PD(MAX) = (125°C − 25°C) 220 = 0.455W
for SOT23-5 package
(EQ.5)
Capacitor Characteristics
PD(MAX) = (125°C − 25°C) 90 =1.111W
for TDFN-6 package
More consideration should be taken when selecting the
capacitor because its capacitance can vary with
temperature. The capacitor type X7R or X5R, which
operates over a temperature range of -40℃ to +85℃,
will only vary within ±15%. Some large value ceramic
capacitors are manufactured with Z5U or T5V
temperature characteristics. Their capacitance can drop
by more than 50% as the temperature goes from 25℃ to
85℃. Therefore the capacitor type X7R or X5R is
recommended in applications where the ambient
temperature will change significantly above or below
25℃.
(EQ.6)
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. For EUP7907A packages, the Figure 3 of
derating curves allows the designer to see the effect of
rising ambient temperature on the maximum power
allowed.
No Load Stability
The EUP7907A will remains stable and in regulation
with no external load. This is special important in CMOS
RAM keep-alive applications.
Thermal Considerations
Thermal protection limits power dissipation in
EUP7907A.When the operation junction temperature
exceeds 170°C, the OTP circuit starts the thermal
shutdown function and turns the pass element off. The
pass element turn on again after the junction temperature
cools by 30°C.
Figure 5. Power Dissipation for EUP7907A Packages
The EUP7907A is available in two standard packages:
TDFN-6 and SOT23-5 packages.
For continuous operation, do not exceed absolute
maximum operation junction temperature 125°C. The
power dissipation definition in device is:
(EQ.3)
PD = V − VOUT ×IOUT + V ×IQ
( )
IN
IN
DS7907A Ver 1.1 M ar. 2009
10
EUTECH [ EUTECH MICROELECTRONICS INC ]
