Features• AEC-Q100 qualified• Operating temperature range: -40 °C to 135 °C for Tj• Designed for iso-buck topology• 4 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

DescriptionThe STEVAL-A6986IV2 evaluation board is based on ST A6986I automotive 38 V, 5W synchronous iso-buck converter for isolated applications.

The primary output voltage can be accurately adjusted, whereas the isolatedsecondary output is generated by a transformer. No optocoupler is required.

The primary sink capability (typ. 1.9 A) allows a proper energy transfer to thesecondary 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 deviceoperates in forced PWM.

The 300 ns blanking time filters oscillations generated by the transformer leakageinductance and makes the solution more robust.

Pulse by pulse current sensing on both power elements implements an effectiveconstant current protection on the primary side. Due to the primary reverse currentlimit, the secondary output is protected against short-circuit events. The secondaryvoltage is stabilized over current by using a power transistor and a shunt voltagereference (TL431).

The evaluation board generates an isolated voltage (around 5 V, easily adjustable),especially suitable for applications requiring a single isolated supply.

Product summary

38 V, 5 W synchronousiso-buck converterevaluation board withsingle isolated outputbased on the A6986I

STEVAL-A6986IV2

Automotive 38 V, 5 Wsynchronous iso-buckconverter for isolatedapplications

A6986I

Automotive 150 V,1 A power Schottkyrectifier

STPS1150AY

Adjustable micropowershunt voltagereference

TL431

Applications

Main Inverter(ElectricTraction)

On BoardCharger (OBC)

38 V, 5 W synchronous iso-buck converter evaluation board with single isolated output based on the A6986I

STEVAL-A6986IV2

Data brief

DB4367 - Rev 2 - July 2021For further information contact your local STMicroelectronics sales office.

www.st.com

1 Isolated voltage adjustment

If different isolated voltage values are required, simple voltage adjustment is possible by changing the resistordivider composed of R12 and R13 according to the following equation:VISO = 2.49R12 + R13R13

Note: A fine tuning of the R11 value might be necessary.

STEVAL-A6986IV2Isolated voltage adjustment

DB4367 - Rev 2 page 2/5

2 Schematic diagrams

Figure 1. STEVAL-A6986IV2 board schematic

GND1

GND1 GND2

GND2 GNDiso

VISO+

GND1

EMI FIlter

ferrite bead

0 ohm

ZB1175-AE

TL431

2STR1215

n.m.

10uF

Optional circuitry for improved load regulation

R8 180

TP5VIN

R356k

VOUT2 TP12

C16 n.m.

C20

4.7uF

C8

10uF

C19

4.7uFTP4

GNDpri

R17

L3

4.7uH

TP7GND1

U2

11

22

33

44

55

66

77

88

U3

C18

4.7uF

L4

C15 68p

C4

4.7p

C9

100n

F

R1

6.8k

R12

11kC21

TP6VOUT1

C17

R13

10.7k

D12 1

TP9 GNDiso

TP8 VISO+

C1

470n

F

Q1

U1 A6986I

RST

1

VCC2

SS/INH3

SYNCH

4

FSW5

MLF6

COMP7

DELAY8

FB9

SGND

10

PGND

11

PGND

12

LX13

LX14

VIN15

VBIAS16

EP

17

R11

100

R2

1.3k

C13

1uF

R18

n.m.

TP11GND2

C2

68nF

C5

680p C11

10uF

R16

n.m.

Note: The evaluation board embeds an input EMI filter (on the bottom side). If the filter is not necessary or needs to be bypassed for any test, a 0 Ωresistor can be placed on R16 (bottom side).

DB

4367 - Rev 2

page 3/5

STEVAL-A

6986IV2Schem

atic diagrams

Revision history

Table 1. Document revision history

Date Version Changes

08-Mar-2021 1 Initial release.

31-Jul-2021 2 Updated cover page product summary table.

STEVAL-A6986IV2

DB4367 - Rev 2 page 4/5

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STEVAL-A6986IV2

DB4367 - Rev 2 page 5/5