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SLLU298 – May 2018
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ISO5852SDW Driving and Protecting SiC and IGBT Power Modules
It includes two isolated channels with the following key functional blocks:
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20A source/sink 5.7 kVrms Isolated driver using ISO5852SDW driver IC
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Split rail bias supply using two 424 kHz transformer drivers SN6505B to generate sepa17 V rail
for turn ON and -5 V rail for turn OFF
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Input logic block with shoot-through prevention
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Output protection and diagnostic block
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Analog amplifiers AMC1301 to monitor temperature inside the module and input voltage rail with 5.0
kVrms isolation
1.3.3
Isolated Gate Driver ISO5852S
ISO5852SDW, isolated driver in SOIC-16DW package with 8.0mm creepage and clearance providing
5.7kVrms reinforced isolation, includes all main short circuit protection features. ISO5852SDW driver IC
employs TI proprietary high voltage, low propagation delay, CMTI immune capacitive isolation technology.
The list of isolation safety certifications from agencies like VDE, CSA, UL and CQC is provided in related
datasheet. Short, 76 ns propagation delay with only 20 ns skew allows accurate control of power devices.
Figure 1
includes block diagram of ISO5852SDW driver.
Primary side voltage Vcc1 is controlled by internal UVLO1 circuit with 2.25Vmax rising threshold and
1.7Vmin falling threshold. Inverting and non-inverting input signals IN- and IN+ have CMOS thresholds
derived from Vcc1 voltage: 0.7 x Vcc1 max rising and 0.3 x Vcc1 min falling accordingly. Secondary side
voltage Vcc2 can go up to 35V abs. max. Turn ON drive voltage between Vcc2 and GND2 pins is
controlled by internal UVLO2 circuit with 13Vmax rising threshold and 9.5V min falling threshold. The split
sink/source output allows setting optimal turn ON and turn OFF time by selecting separate gate resistors
between driver output and gate of power device. This driver has all necessary short circuit protection
features including desaturation current sensing, soft short circuit turn OFF, Miller gate clamp, fault, power
ready and reset signals.
1.3.4
Split-Rail Bias Supply using SN6505B
Split rail bias supply generates 17V turn ON, and -5V turn OFF voltages using two push-pull transformer
drivers SN6505B operating at 424kHz and housed in 6-pin small SOT-23 package.
The SN6505B is supplied through Vcc terminal from external source in the range from 2.25 to 5.5V. Input
voltage is controlled by UVLO circuit having rising threshold 2.25Vmax and falling threshold 1.7V min.
Internal oscillator operates at 424kHz typical frequency within range from 363 kHz min. to 517 kHz max..
The SN6505 employs spread spectrum clocking technique to minimize EMI. The output stage includes 1A
push-pull switches rated up to 16 V abs. max. The switches are protected by current limit circuit tripped at
1.7 A typ. level. The device also protected by thermal shutdown circuit triggered at 168 ºC typical
threshold and returning back to normal operation at 150 ºC typical. Additional features include soft start
and Enable signal. Because there is no closed feedback loop in this inexpensive bias supply solution, it
operates like DC-DC transformer and requires low tolerance primary voltage to maintain output voltages
within ±10% range.
1.3.5
Input Logic
Input logic block fulfills the following functions:
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Provides additional UVLO and OVLO protection of secondary side drive voltages using sensing on
primary side Vcc based on window comparator TPS3700
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Generates separate fault signals for each channel when the short circuit occurs along with general
system fault signal using AND logic CMOS IC SN74AHC1G08QDBVRQ1
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Generates combined Reset signal output for both isolated channels
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Provides isolated differential output signals from temperature and input rail monitoring circuits using
isolated amplifiers AMC1301
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Can be set for driver outputs overlapping prevention mode by having shunt resistors R48 and R52 in
place. To allow outputs overlapping simply remove shunt resistors R48 and R52.