AN836 Datasheet, PDF (2/5 Pages) STMicroelectronics – LOW FORWARD VOLTAGE SCHOTTKY DIODE

AN836 APPLICATION NOTE
Table 1. Main Characteristics of Schottky
PART NUMBER
PACKAGE
Io
STPS125U
SOD6
STPS5L25B
DPAK
STPS10L25D
TO220AC
STPS15L25D/G
D2PAK/TO220AC
STPS20L25CT
TO220AB
STPS20L25CG
D2PAK
Note: 1. Main characteristics of the 25V low VF Schottky
A
1
5
10
15
2x10
2x10
V_F
(Io,125°C)
typ
Max
mV
mV
390⁽¹⁾
460⁽¹⁾
310
350
300
350
300
350
300
350
300
350
I_R
(125°C, 25V)
Max
mA
2⁽¹⁾
175
400
640
400
400
OR-ING SCHOTTKY
To increase system reliability, power supplies are sometimes connected in parallel (Fig.1).
Figure 1. OR-ing Schottky in redundant power supply
POWER
SUPPLY
1
IOUT/n
IOUT
VOUT
3.3V, 5V or 12V
POWER
SUPPLY
2
IOUT/n
POWER
SUPPLY
n
IOUT/n
The Schottky diodes are connected in series with the output of each power supply. In the steady state a
continuous current (I_OUT/n) flows in each Schottky. Obviously in this case there are no reverse losses.
When a power supply fails, the corresponding ORING diodes ceases to carry current and the system out-
put voltage is not disturbed. The OR-ing diode then sees the reverse voltage V_OUT.
In this application the most critical parameter is the forward voltage drop in order to maintain the best ef-
ficiency of the system. A breakdown voltage of 10V is sufficient for output voltage of 5V and 3.3.V.
The trade-off has been chosen to obtain a low forward voltage. In this application we can accept a high
leakage current because when the diode is blocked the reapplied voltage is low (3.3V or 5V), the junction
temperature is also low because there are only reverse losses. So it’s easy to keep reverse losses under
control.
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