Avago Technologies ACPL-339J-000E User Manual
Page 6
6
a) Operations of various outputs
The outputs (V
OUTP
, V
OUTN
, V
GMOS
and FAULT) of each ACPL-339J are governed by the combination of I
F
(the LED
current), UVLO and DESAT conditions. Once the UVLOP+ and UVLON– signals are not active (V
CC2
- V
E
> V
UVLOP+
, V
E
- V
EE
> V
UVLON+
), V
OUTP
is allowed to go low and V
OUTN
is allowed to go high. Thereafter, the DESAT (pin 15) detection feature
of the ACPL-339J will be the primary source of IGBT/Power MOSFET protection. DESAT will remain functional until V
CC2
-
V
E
is decreased below V
UVLOP-
or V
E
- V
EE
is decreased below V
UVLON-
. Therefore, the DESAT detection and UVLO features
of the ACPL-339J work alternatively to ensure constant IGBT/MOSFET protection.
Table 1 shows the possible output combinations for Fault, V
outp
, V
outn
and V
gmos
under the influence of different UVLO
and DESAT operating conditions, whether they are active or not.
Table 1
I
F
UVLOP and UVLON
DESAT Function
Pin 7 (FAULT) Output
V
OUTP
V
OUTN
V
GMOS
X
Active
Not Active
High
High
Low
V
E
ON
Not Active
Active (with DESAT fault)
High
High
Low
V
E
ON
Not Active
Active (no DESAT fault)
Low
Low
High
V
EE
OFF
Not Active
Not Active
Low
High
Low
V
EE
Note:
Normal operating condition is highlighted in blue in the table; X denotes Don’t Care; Logic output of V
GMOS
will be changed from V
EE
to V
E
when
UVLON is active. This will ensure that MN3 is turned on to shut down the IGBT/SiC FET when insufficient power supply V
E
-V
EE
is applied.
b) Soft-shutdowns from DESAT and UVLO faults
The DESAT pin of each device monitors its IGBT V
ce
voltage. The internal DESAT fault detection circuitry must remain
disabled for a short time period following the turn-on of the IGBT to allow the collector voltage to fall below the DESAT
threshold. This time period, called the DESAT blanking time, is controlled by the internal DESAT charge current, the
DESAT voltage threshold, and the external DESAT blanking capacitor (C8, at 100 pF). The nominal blanking time is
calculated in terms of external capacitance (C
BLANK
), FAULT threshold voltage (V
DESAT
), and DESAT charge current (I
CHG
)
as T
BLANK
= C
BLANK
× V
DESAT
/ I
CHG
. The nominal blanking time with the recommended 100 pF capacitor is 100 pF * 8 V /
250 µA = 3.2 µsec. This nominal blanking time also represents the longest time it will take for each ACPL-339J to respond
to a DESAT fault condition. After T
BLANK
time, both V
OUTP
and V
OUTN
outputs will turn off the respective external Q1 and
Q2 MOSFETs and V
GMOS
switches from Low to High, turning on an external Q3 pull-down MOSFET, to ‘softly’ turn off the
IGBT. Also activated is an internal feedback channel that brings the isolated FAULT output from Low to High to notify the
microcontroller of the fault condition.
Once fault is detected, the output will be muted for T
MUTE
time. All input LED signals will be ignored during the mute
period to allow the driver to completely do a soft shutdown of the IGBT. The fault is auto-reset upon the 1 ms (typical)
mute time (T
MUTE
) timeout or upon the change in IN1 status from High to Low transition, whichever is later. In this way
there is a minimum timeout, yet there is still flexibility of lengthening the timeout.
When a DESAT fault is detected, its device’s V
GMOS
output switches from Low to High, turning on the external Q3 MOSFET
pull-down device. Q3 slowly discharges the IGBT gate voltage at a decay rate corresponding to the RC constant of RS
and C
IN
(the IGBT input capacitance). Based on a RS of 330
Ω (as in R10) and C
IN
of 10 nF(from the external connected
capacitor at Q5 or Q6), the entire soft shut down will decay in 4.8 * 330
Ω * 10 nF = 15.8 µs. Soft shutdown prevents fast
changes of the collector current that could cause damaging voltage spikes due to lead and wire inductance. Similarly,
when under voltage operation occurs during normal operation, its device’s V
GMOS
output switches from Low to High,
turning on the external Q3 MOSFET pull-down device. Q3 slowly discharges the IGBT gate voltage at a decay rate
corresponding to the RC constant of RS and C
IN
(the IGBT input capacitance). The entire soft shutdown will decay in 15.8
µs to prevent fast changes in the collector current.