Datasheet
R
S
DESAT
V
E
V
EE-L
V
CC2
V
C
V
OUT
V
EE-P
15V
ISO5500
100
pF
D
DESAT
R
g
+
-
16
15
14
12
13
11
10
9
15V
D
S
(opt.)
V
FW-inst
+
-
V
FW
V
EE-L
ISO5500
SLLSE64C –SEPTEMBER 2011–REVISED JUNE 2013
www.ti.com
Figure 68. DESAT Pin Protection with Series Resistor and Optional Schottky Diode
DESAT DIODE AND DESAT THRESHOLD
The DESAT diode’s function is to conduct forward current, allowing sensing of the IGBT’s saturated collector-to-
emitter voltage, V
CESAT
, (when the IGBT is "on") and to block high voltages (when the IGBT is "off"). During the
short transition time when the IGBT is switching, there is commonly a high dV
CE
/dt voltage ramp rate across the
IGBT. This results in a charging current I
CHARGE
= C
D-DESAT
x d
VCE
/dt, charging the blanking capacitor.
To minimize this current and avoid false DESAT triggering, fast switching diodes with low capacitance are
recommended. As the diode capacitance builds a voltage divider with the blanking capacitor, large collector
voltage transients appear at DESAT attenuated by the ratio of 1+ C
BLANK
/ C
D-DESAT
.
Table 1 lists a number of fast-recovery diodes suitable for the use as DESAT diodes.
Because the sum of the DESAT diode forward-voltage and the IGBT collector-emitter voltage make up the
voltage at the DESAT-pin, V
F
+ V
CE
= V
DESAT
, the V
CE
level, which triggers a fault condition, can be modified by
adding multiple DESAT diodes in series: V
CE-FAULT(TH)
= 7.2 V – n x VF (where n is the number of DESAT
diodes).
When using two diodes instead of one, diodes with half the required maximum reverse-voltage rating may be
chosen.
Table 1. Recommended DESAT Diodes
PART NUMBER MANUFACTURER t
rr
(ns) V
RRM-max
(V) PACKAGE
STTH112 STM 75 1200 SMA, SMB, DO-41
MUR100E Motorola 75 1000 59-04 (axial leaded)
MURS160T3 Motorola 75 600 Case 403A (SMD)
UF4007 General Semi. 75 1000 DO-204AL (axial leaded)
BYM26E Philips 75 1000 SOD64 (axial leaded)
BYV26E Philips 75 1000 SOD57 (axial leaded)
BYV99 Philips 75 600 SOD87 (axial leaded)
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