Application Notes

Application Note
The PMEG1020EA and PMEG2010EA
MEGA Schottky diodes
Philips Semiconductors
AN10230-01
The PMEG1020EA and PMEG2010EA MEGA Schottky diodesa pair designed for high efficiency rectification
by Martin Lübbe
Introduction
Schottky diodes have found various applications in the fields of power supply and power management. Some
characteristic examples are reverse polarity protection, OR’ing circuits and switch mode power supplies. These
applications all exploit the reduced forward voltage VF at a given forward current IF as compared to standard pnswitching diodes.
With the MEGA type range Philips launched a whole portfolio of novel Schottky diodes designed especially to
further improve the efficiency in the respective application.
The efficiency improvements are twofold: On the one hand the MEGA Schottkys are offered in small SMD
packages like SOD323 (SC-76), SOD523 (SC-79) or the brand new, ultra flat SOT666, allowing a more efficient use
of the available board space. On the other hand we developed novel production processes to further increase the
electrical performance of MEGA Schottkys in the medium power range up to a few Amps.
In the following we will present two diodes, which very clearly illustrate the idea behind the MEGA portfolio,
namely the PMEG1020EA and PMEG2010EA types. Both types are available in SOD323 (SC-76) and in the new
ultra flat SOT666 (extension EV instead of EA).
Main features
The main parameters of both diodes are summarized in Table 1 and typical forward and reverse characteristics can
be seen in Fig. 1.
Table 1: Electrical comparison of PMEG2010EA and PMEG1020EA MEGA Schottky diodes.
Conditions
PMEG2010EA
PMEG1020EA
Unit
VR
Continuous reverse voltage
-
20
10
V
IF
Continuous forward current
-
1
2
A
VF1
Forward voltage
IF = 1A
480
280
mV
VF2
Forward voltage
IF = 2A
-
350
mV
IR1
Reverse current
VR = 8V
0.007
1
mA
IR2
Reverse current
VR = 15V
0.01
-
mA
CD
Diode capacitance
VR = 5V
19
37
pF
Page 1 of 6
The PMEG1020EA and PMEG2010EA
MEGA Schottky diodes
Application Note
Reverse current / mA
EA
4S
20
10
S7
PM
EG
100
1P
EG
10
20
1000
B4
EA
3
Philips Semiconductors
PM
Forward current / mV
AN10230-01
10
1
0
100 200 300 400 500 600 700
Forward voltage / mV
1
P
G10
ME
A
20E
0.1
1 PS
0.01
74S
B4 3
EG 2
PM
0
5
E
010
10
A
15
20
Reverse voltage / V
Fig. 1:Forward (left) and reverse (right) bias characteristics for the PMEG2010EA and
PMEG1020EA MEGA Schottky diodes as compared to the 1PS74SB43 standard
Schottky diode.
In Fig. 1 we also included the typical curves for the well-known 1PS74SB43 rectifier, which is available in the SC-74
package.
It can be clearly seen that the forward and reverse performances of the PMEG2010EA very closely match the
performance of the 1PS74SB43 standard Schottky diode, which has twice the size of the PMEG2010EA. This
example clearly illustrates the first branch of the MEGA Schottky innovation: Same performance on less required
board space.
For a huge part of medium power applications with currents up to 1 A the PMEG2010EA will be the standard
diode of choice. Especially for DC/DC converter applications this diode is also available in combination with NPN
or PNP transistors in a single SOT457 (SC-74) package (typenames PMEM4010PD and PMEM4010ND).
However, especially in battery driven equipment the efficient use of the available power is of superior importance.
For these cases we further extended the technologic limits and designed the PMEG1020EA.
Regarding Fig. 1 the differences of PMEG1020EA as compared to PMEG2010EA are obvious: The VF and thus
the forward power loss PF is drastically reduced in the whole current range. At the same time due to a fundamental
physical fact the reverse current IR increases by a considerable amount. The consequences of this behavior are best
illustrated by calculating an application example.
Application example
To further compare the two MEGA diodes we calculate a practical example: It has been stated before that a main
application for the PMEG1020EA is battery driven equipment. In many of these systems different supply voltages
are needed for the various functional blocks. DC/DC converters mainly realize the required voltage conversion
from the varying battery voltage to the different system voltages.
Let’s assume we have to convert the voltage of 3.6 V from a Li- ion battery to a voltage of 1.5 V, which is required
by many modern ICs. For this purpose the buck converter topology is widely used (see Fig. 2). The duty cycle of the
converter is determined by the ratio of the input and the output voltage. For the voltage conversion of 3.6 V down
to 1.5 V we get a duty cycle of approx. 40 % for the transistor and 60 % for the diode. During the on- state of the
Page 2 of 6
Application Note
The PMEG1020EA and PMEG2010EA
MEGA Schottky diodes
Philips Semiconductors
AN10230-01
Vin = 3.6 V
Vin = 3.6 V
VR = 3.6 V
IF = 100 mA
RL
RL
Fig. 2: Schematics a buck converter as calculated in the text. Left hand side: Diode on- state, transistor
switch is open. Right hand side: Diode off- state, transistor switch is closed.
diode the output current Iout is flowing through the diode (see Fig. 2, left) while during the off- state the diode is
reverse biased with the whole input voltage Vin (see Fig. 2, right).For an output current of 100 mA and a Schottky
junction temperature Tj of 25 °C the calculation of the power loss can be found in Table 2.
Table 2: PMEG2010EA and PMEG1020EA efficiency calculation for the presented Buck converter
application example.
PMEG2010EA
PMEG1020EA
Unit
Forward voltage at Iout = 100mA
VF (see Fig. 1)
300
170
mV
Power loss in forward bias
PF = VF x 100 mA
30
17
mW
Reverse current at Vin = 3.6 V
IR (see Fig. 1)
0.004
0.6
mA
Power loss in reverse bias
PR = IR x 3.6 V
<0.1
2.2
mW
Mean power loss in cycle for 60%
diode duty factor
Ptot in percentage of Pout
Pout = 1.5 V x 100 mA = 150 mW
Ptot=
0.6 x PF + 0.4 x PR
18
11
mW
Ptot/ Pout
12
7.3
%
Comparing the PMEG2010EA and the PMEG1020EA the power loss in percentage of the output power is reduced
from 12 % to 7.3 %, which is a reduction by 40 %. If we assume that the diode accounts for half of the total power
dissipation we get an overall efficiency improvement from 76 % (100 % - 12 % - 12 %) to 80.7 % (100 % - 12 % 7.3%). At higher diode duty cycles or lower input voltages Vin the improvement will be even more pronounced.
For the following part it is important to note that in case of the highly efficient PMEG1020EA the reverse power
loss PR is a significant part of the total power loss. In our exemplary buck converter application this fact limits the
operating range of the PMEG1020EA towards high temperatures as the reverse current increases with rising
temperature. In the calculation of Table 2 we were also able to neglect the self- heating of the diode due to the very
limited dissipated power. At high ambient temperatures Ta we will have to include the influence of the rising
junction temperature Tj.
Temperature dependence
Fig. 3 shows the variation of the main parameters VF and IR for different junction temperatures. The forward
voltage at a given current is reduced by approximately 1 mV for a temperature rise of 1 °C while the reverse current
doubles each 15 °C.
Page 3 of 6
The PMEG1020EA and PMEG2010EA
MEGA Schottky diodes
Application Note
AN10230-01
Philips Semiconductors
Reverse current / mA
Forward voltage / mV
350
IF = 100mA
300
PME
G
250
2010
EA
200
PME
G
150
1020
EA
100
20
40
60
VR = 3.6V
100
2
10
EG
M
P
10
1
0
01
G2
E
PM
0.1
EA
0.01
1E-3
20
80
A
0E
Junction temperature / °C
40
60
80
100
120
Junction temperature / °C
Fig. 3: Temperature dependence of the forward voltage (left hand side) and the reverse
current (right hand side) for the PMEG2010EA and PMEG1020EA MEGA Schottky
diodes.
The junction temperature, which is reached in the application, depends on the ambient temperature, the dissipated
power and the thermal resistance Rth(j-a) from junction to ambient. The calculation of the junction temperature Tj is a
complicated task, which we will skip in this paper. Just the result for different ambient temperatures is shown in
Table 3. The table is very similar to Table 2, only two rows were added for the ambient temperature Ta and the
junction temperature Tj, respectively.
Table 3: Ambient temperature dependence of efficiency improvement using PMEG1020EA instead of
PMEG2010EA.
PMEG2010EA
PMEG1020EA
Unit
Ambient temperature Ta
25
35
45
55
65
25
35
45
55
65
°C
Junction temperature Tj
32.8
42.5
52.2
61.9
71.6
29.7
39.7
49.9
60.5
72.0
°C
VF (see Fig. 3)
290
278
265
253
241
159
146
133
120
106
mV
PF = VF x 100 mA
29.0
27.8
26.6
25.3
24.1
15.9
14.6
13.3
12.0
10.6
mW
IR (see Fig. 3)
0.02
0.03
0.05
0.08
0.14
0.69
1.17
2.00
3.50
6.42
mA
PR = IR x 3.6 V
0.07
0.11
0.18
0.30
0.50
2.49
4.22
7.21
12.6
23.1
mW
Ptot=
0.6 x PF + 0.4 x PR
17.4
16.7
16.0
15.3
14.7
10.5
10.4
10.9
12.2
15.6
mW
12
11
11
10
10
7
7
7
8
10
%
Ptot/ Pout
The calculation bases on two assumptions: First we assumed the devices to be placed on standard footprint without
extra cooling areas. In this case we get an Rth(j-a) value of 450 K/W. The second assumption is an operating
frequency, which is high enough to get an almost constant temperature during the diodes on and off cycle. As in
DC/DC converters normally the operating frequency is above 50 kHz to keep the size and the costs of the passive
components small this assumption is fulfilled.
Page 4 of 6
Application Note
The PMEG1020EA and PMEG2010EA
MEGA Schottky diodes
Philips Semiconductors
AN10230-01
Regarding Table 3 the main difference is obvious: While the efficiency of the PMEG2010EA diode increases with
rising ambient temperature, the effect is the other direction for the PMEG1020EA. The reason is the higher power
loss under reverse bias for the PMEG1020EA.
At an ambient temperature of 65 °C (149 °F) the power losses are comparable for both diodes. For even higher
ambient temperatures the results very much depend on the exact nature of the mounting and the cooling conditions
including the amount of air circulation. We therefore did not perform the calculation. In these cases the usability of
the PMEG1020EA has to be thoroughly investigated which exceeds the scope of the present paper.
Conclusion
We presented two diodes of the new Philips MEGA Schottky typerange: The PMEG2010EA and the
PMEG1020EA. We illustrated how these diodes can yield an electrical performance comparable to standard
Schottky diodes in considerably larger packages. For an exemplary DC/DC conversion application we have shown
how using the PMEG1020EA can boost the diode efficiency.
Further we investigated the temperature dependence of the derived efficiency and found that at an ambient
temperature of 65 °C (149 °F) the efficiencies for both diodes are aligning.
In conclusion, the PMEG2010EA is a standard diode for medium power applications, which yields top class
performance in a very small package.
The PMEG1020EA on the other hand is the diode of choice if efficient use of the available power is extremely
important. Due to the increasing losses at higher temperatures this diode is most suitable in applications with limited
temperature ranges like handheld devices, laptops or temperature controlled circuit boards.
Page 5 of 6
The PMEG1020EA and PMEG2010EA
MEGA Schottky diodes
AN10230-01
Application Note
Philips Semiconductors
For further information please visit our discrete semiconductors web site
(http://www.semiconductors.philips.com/products/standard/discretes/)
or contact your next sales representative for updated information.
© Koninklijke Philips Electronics N. V. 2003
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Page 6 of 6
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