STMicroelectronics A6986I
A6986I - automotive 38 V, 5 W synchronous Iso-Buck converter
The A6986I is an automotive grade device specifically designed for the isolated buck topology. The 100% duty cycle capability and the wide input voltage range meet the cold crank and load dump specifications for automotive systems. The primary output voltage can be accurately adjusted, whereas the isolated secondary output is derived by using a given transformer ratio. No optocoupler is required. The primary sink capability typically up to 1.9 A (even during soft-start) allows a proper energy transfer to the secondary side as well as enabling a tracked soft-start of the secondary output.
The control loop is based on a peak current mode architecture and the device operates in forced PWM. The 300 ns blanking time filters oscillations, generated by the transformer leakage inductance, making the solution more robust. Pulse-by-pulse current sensing on both power elements implements an effective constant current protection in the primary side. Due to the primary reverse current limit, the secondary output is protected against short-circuit events. A primary output voltage supervisor, which notifies primary output voltage regulation through the RST open collector output, overvoltage protection, adjustable switching frequency, synchronization and a programmable soft-start are also available. For traditional buck topology in automotive application the A6986 / A6985F / A6986F / A6986H is recommended.
Features
- AEC-Q100 qualified
- Operating temperature range:
- -40 °C to 150 °C
- Designed for iso-buck topology
- 4 V to 38 V operating input voltage
- Primary output voltage regulation / no optocoupler required
- 1.9 A typical sink peak primary current capability
- Peak current mode architecture in forced PWM operation
- 300 ns blanking time
- 8 µA IQ-SHTDWN
- Adjustable fSW and synchronization
- Embedded primary output voltage supervisor
- Adjustable soft-start time
- Internal primary current limiting
- Overvoltage protection
- RDS(on) HS = 180 mΩ, RDS(on) LS = 150 mΩ
- Thermal shutdown
STEVAL-A6986IV1 - 38 V, 5 W synchronous iso-buck converter evaluation board with dual isolated output based on the A6986I
The STEVAL-A6986IV1 evaluation board is based on ST A6986I automotive 38 V, 5 W synchronous iso-buck converter for isolated applications. The primary output voltage can be accurately adjusted, whereas the isolated secondary output is generated by a transformer. No optocoupler is required.
The primary sink capability (typ. 1.9 A) allows a proper energy transfer to the secondary side and enables a tracked soft-start of the secondary output.
The control loop is based on a peak current mode architecture and the device operates in forced PWM.
The 300 ns blanking time filters oscillations generated by the transformer leakage inductance and makes the solution more robust. Pulse by pulse current sensing on both power elements implements an effective constant current protection on the primary side. Due to the primary reverse current limit, the secondary output is protected against short-circuit events. The secondary voltage is stabilized over current by using a power transistor and a shunt voltage reference (TL431).
The evaluation board generates two isolated voltages (positive around 18 V and negative between 4 V and 5 V), especially suitable for supplying IGBT/SiC MOSFET gate driver. A simple bypass enables the supply of a single isolated voltage.
STEVAL-A6986IV2 - 38 V, 5 W synchronous iso-buck converter evaluation board with single isolated output based on the A6986I
The STEVAL-A6986IV2 evaluation board is based on ST A6986I (automotive 38 V, 5 W synchronous iso-buck converter for isolated applications). STEVAL-A6986IV2. The primary output voltage can be accurately adjusted, whereas the isolated secondary output is generated by a transformer. No optocoupler is required.
The primary sink capability (typ. 1.9 A) allows a proper energy transfer to the secondary side as well as enables a tracked soft-start of the secondary output.
The control loop is based on a peak current mode architecture and the device operates in forced PWM.
The 300 ns blanking time filters oscillations generated by the transformer leakage inductance and makes the solution more robust.
Pulse by pulse current sensing on both power elements implements an effective constant current protection on the primary side. Due to the primary reverse current limit, the secondary output is protected against short-circuit events. The secondary voltage is stabilized over current by using a power transistor and a shunt voltage reference (TL431).
The evaluation board generates an isolated voltage (around 5 V, easily adjustable), especially suitable for applications requiring a single isolated supply.
STEVAL-A6986IV3 - Isobuck-boost converter with four selectable dual voltages
The STEVAL-A6986IV3 is an evaluation board based on ST A6986I.
The A6986I is designed for isolated applications and normally implements an iso-buck architecture.
The STEVAL-A6986IV3 board adopts an inverting buck-boost topology at the primary side (instead of a standard buck), hence building an isobuck-boost (so called from now on).
The advantages in using the isobuck-boost instead of a buck are mainly: higher deliverable power at the secondary side, optimization of the transformer design.
The input voltage is up to 28 V. Since the primary side performs an inverting buck-boost conversion, the primary output voltage is negative.
The secondary side of the board consists of four independent windings, each one intended to provide the supply for a gate driver (see block diagram on page 2) thanks to a very accurate post regulation.
The isobuck-boost architecture exploits the power capability of the A6986I, delivering up to 60 mA for three secondary channels and up to 180 mA for the fourth one.
A microswitch provides the possibility to select two regulated voltage pairs for each channel: 18 V / - 5 V or 15 V / - 8 V. The regulation of these voltages is achieved by using the LDH40 (for the positive voltage) and a shunt regulator TL431B (for the negative voltage). The expanded output voltage range (up to 22 V) of the LDH40 makes it ideal for this kind of application.
Thanks to the LDH40 and the TL431B, the described post regulation allows a voltage accuracy well below ±1%.
The availability of four well-regulated dual voltages makes this solution ideal for gate driving in three-phase inverters.
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