EUP7903
Output capacitor
The EUP7903 is designed specifically to work with very
small ceramic output capacitors. A 1uF to 10uF
capacitor with 5mΩ to 500mΩ ESR range is suitable
for the most EUP7903 applications. The ESR of a
typical 1uF ceramic capacitor is around 20mΩ, which
easily meets the ESR requirement for stability.
Capacitor characteristics
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%. However 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
℃
.
No load Stability
The EUP7903 will remain 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
EUP7903.When the device junction temperature exceeds
155°C, the OTP circuit starts the thermal shutdown
function and turns the pass transistor off. The pass
transistor turns on again after the junction temperature
cools down 30°C.
For continuous operation, do not exceed absolute
maximum junction temperature 150°C. The power
dissipation definition in device is:
P
D ( MAX )
=
(125
°
C
−
25
°
C) / 220
=
0.445W
(EQ.5)
for SOT23-5 package
The maximum power dissipation depends on operating
ambient temperature for fixed T
J(MAX)
and thermal
resistance
θ
JA
. For EUP7903 packages, the Figure 5 of
derating curves allows the designer to see the effect of
rising ambient temperature on the maximum power
allowed.
0.6
Maximum Power Dissipation(W)
0.5
0.4
0.3
0.2
0.1
0.0
SOT23-5
0
25
50
75
100
Ambient Temperature( C)
o
125
150
Figure. 5.
Power Dissipation for EUP7903 Package
The EUP7903 is available in the SOT23-5 package.
P
D
=
( V
IN
−
V
OUT
)
×
I
OUT
+
V
IN
×
I
Q
(EQ.3)
The maximum power dissipation depends on the thermal
resistance of IC package, PCB layout, the rate of
surroundings airflow and temperature difference
between junction and ambient. The maximum power
dissipation can be calculated by following formula :
(EQ.4)
Where T
J(MAX)
is the maximum operation junction
temperature 125°C, TA is the ambient temperature and
the
θ
JA
is the junction to ambient thermal resistance.
For recommended operating conditions specification of
EUP7903, where T
J(MAX)
is the maximum junction
temperature of the die (125°C) and TA is the operated
ambient temperature. The junction to ambient thermal
resistance
θ
JA
is layout dependent. For SOT-23-5
package, the thermal resistance
θ
JA
is 220°C/W on the
standard thermal test board. The maximum power
dissipation at T
A
= 25°C can be calculated by following
formula :
DS7903
Ver 1.0
Nov. 2008
P
D ( MAX)
=
(T
J ( MAX)
−
T
A
)
θ
JA
9
EUTECH [ EUTECH MICROELECTRONICS INC ]
