ST STEVAL-L6983IV1 Manuale utente

Introduction

The STEVAL-L6983IV1 evaluation board is based on the L6983I, 38 V, 10 W synchronous iso-buck converter designed for

isolated applications.

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 up to -4.5A (even during soft-start) allows transferring

a proper energy 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 390 ns blanking time filters oscillations,

generated by the transformer leakage inductance, making the solution more robust.

The compact QFN-16 3x3mm package and the internal compensation of the L6983I help minimize the design complexity and

size.

The switching frequency can be programmed in the 200 kHz - 1 MHz range with an optional spread spectrum for improved

EMC.

The EN pin provides the enable/disable functionality. The typical shutdown current is 2 µA when disabled. As soon as the EN

pin is pulled-up, the device is enabled, and the internal 1.3 ms soft start takes place.

The L6983I features the power good open collector that monitors the FB voltage. Pulse by pulse, the current sensing on both

power elements implements an effective constant current protection. The thermal shutdown prevents thermal run-away. Due to

the primary reverse current limit, the secondary output is protected against short-circuit events.

The evaluation board generates an isolated unregulated voltage and provides the possibility to use a post-regulation to generate

a dual voltage (layout available on the bottom of the PCB, components not mounted).

Figure 1. STEVAL-L6983IV1 evaluation board

Getting started with STEVAL-L6983IV1 evaluation board based on L6983I, 38V,

10W synchronous iso-buck converter for isolated applications

UM3110

User manual

UM3110 - Rev 1 - March 2023

For further information contact your local STMicroelectronics sales office. www.st.com

1Getting started

1.1 Safety instructions

This board is intended to be used by skilled technical personnel who are suitably qualified and familiar with the

installation, use, and maintenance of power electronic systems. The same personnel must be aware of and must

apply national accident prevention rules.

The electrical installation has to be completed in accordance with the appropriate requirements (that is, cross-

sectional areas of conductors, fusing, and GND connections).

1.2 Functional block diagram

Figure 2. STEVAL-L6983IV1 block diagram

1.3 Features

• Designed for iso-buck topology

• 4 V to 38 V operating input voltage

• Primary output voltage regulation

• No optocoupler required

• 4.5 A source/sink peak primary current capability

• Peak current mode architecture in forced PWM operation

• 300 ns blanking time

• 25 μA operating quiescent current

• 200 kHz to 1 MHz programmable switching frequency. Stable with low ESR capacitor: min 2µF

• Internal compensation network

• 2 μA shutdown current

• Internal soft start

• Enable

• Overvoltage protection

• Thermal protection

• Optional spread spectrum for improved EMC

• Power good

• Synchronization with external clock

• QFN16 3x3 mm package

UM3110

Getting started

UM3110 - Rev 1 page 2/29

2How to use the board

The STEVAL-L6983IV1 is configured to deliver 5 V at the primary non-isolated output and an unregulated voltage

at the isolated output that varies with the applied load (see load regulation curves in section 8). The switching

frequency is set to 400 kHz.

To use the board, follow the procedure below.

Step 1. Connect the power supply to the test points of VIN and GND.

Step 2. Connect the load to the primary non-isolated output (if any) as well as to the secondary isolated output.

Step 3. Set the supply voltage VIN from 8 V to 38 V and switch the power supply on.

Step 4. Regulate both active loads.

Figure 3. STEVAL-L6983IV1 basic test setup

Note: The STEVAL-L6983IV1 embeds the L6983I. The STEVAL-L6983IV1 is however suitable for the

A6983I too. If the A6983I should be tested, simply replace the L6983I with the A6983I.

UM3110

How to use the board

UM3110 - Rev 1 page 3/29

3Connectors and test points

3.1 VIN – TPxx

This connector is used for the input supply voltage. This voltage is provided, through the input EMI filter, to the

device VIN pin.

A power supply ranging from 4 V to 38 V should be connected to this test point, setting a proper current limit.

The wire connection should be as short as possible to avoid or limit possible oscillations due to the parasitic

inductance of the wire and the input capacitor.

3.2 GND1 and GNDprim – TPxx and TPxxx

GND1 and GNDprim are, respectively, the return path of the input and output capacitors. Wires used for this

connection should be as short as possible.

3.3 VOUT1 – TPxx

This is the connector for the primary non-isolated output voltage. To load the primary output, connect a resistor or

an active load to this test point. Short wires are recommended.

3.4 EN/SYNCH – TPxx

By default, the EN pin is pulled-up to the input voltage through the resistor Ren1. This makes the device always

enabled. The same test-point can be used to apply an external signal for synchronization.

3.5 PGOOD – TPxx

This test point is directly connected to the PGOOD pin.

3.6 VOUTiso – TPxx

This test point provides the isolated output voltage (unregulated). When completely unloaded, the voltage at this

pin could be much higher than the theoretical value (N*VOUT1). Short wire connection from this test point to the

load is recommended.

3.7 GNDiso – TPxx

The voltage at this test point represents the reference for the isolated voltage. Short connection is recommended.

3.8 VISO+, VISO- and VISO_gnd – TPxx

The isolated output voltage can be post-regulated and used to generate a dual voltage. On the bottom side of

the PCB, the layout for post-regulation is available (components to be assembled). If the components of the post

regulation circuitry are assembled, the VISO+, VISO- and VISO_gnd test points provide a positive (VISO+) and

negative voltage (VISO-), both referred to VISO_gnd.

UM3110

Connectors and test points

UM3110 - Rev 1 page 4/29

4Input EMI filter

The STEVAL-L6983IV1 is compliant with CISPR16-4-2 thanks to the embedded EMI filter (bottom side).

The EMI filter consists of:

• A double pi filter with an inductor (Lf2)

• A ferrite bead (Lf1)

• Three MLCC capacitors (Cf1, Cf2, and Cf3)

• An electrolytic bulk capacitor used as bulk energy storage (Cin4)

UM3110

Input EMI filter

UM3110 - Rev 1 page 5/29

5Board setting capability

The STEVAL-L6983IV1 provides the possibility to change some settings according to the application conditions.

Switching frequency

By default, the Rfsw2 is equal to 0 Ω. It sets the switching frequency to 400 kHz and enables the dithering.

By changing the value of Rfsw1, a different switching frequency is set. Using the Rfsw1 instead of Rfsw2 disables

the dithering function (see Table 1. Switching frequency and dithering setting).

Figure 4. Resistors on the PCB used to set the switching frequency and the dithering

Table 1. Switching frequency and dithering setting

Symbol Option RVCC(KΩ) RGND(KΩ) Min. Typ. Max. Unit

FSW

Dithering

1.8 N.C. 200 kHz

0 N.C. 400 kHz

3.3 N.C. 500 kHz

5.6 N.C. 700 kHz

10 N.C. 1000 kHz

No dithering

N.C. 1.8 200 kHz

N.C. 0 360 400 440 kHz

N.C. 3.3 500 kHz

N.C. 5.6 630 700 770 kHz

N.C. 10 900 1000 1100 kHz

Enable thresholds

The STEVAL-L6983IV1 is equipped with the REN1 = 100 kΩ as pull-up resistor to keep the device always

enabled. The power-up threshold can be adjusted by properly selecting the REN1 and REN2, according to the

following equations:

VPowerUP = 1.2 ⋅1 + REN1

REN2

VPowerDown = 1.0 ⋅1 + REN1

REN2

UM3110

Board setting capability

UM3110 - Rev 1 page 6/29

Figure 5. Resistors to enable thresholds setting

Primary output voltage

The primary (non-isolated) output voltage is set to 5 V. If a different voltage is desired, the output resistor divider

should be adjusted according to the following equation:

VOUT_prim = 0.85 ⋅1 + RFB1

RFB2

Figure 6. Resistors of the primary output divider

Note: Changing the value of the primary output voltage implies the variation of the isolated output voltage too.

UM3110

Board setting capability

UM3110 - Rev 1 page 7/29

6Schematic diagrams

Figure 7. STEVAL-L6983IV1 circuit schematic (1 of 2)

Optional (bottom)

10uF 10uF 10uF 100uF 10uF 1uF 1uF

6.8uH

Ferrite 220ohm

75k

360k

0R NM

1uF

100nF

NM NM

1uF

100R 100K

22uF 22uF 22uF NM

300R 180pF

STPS1170AF

10uF

Rfb2

Rbs

Rs1

VIN

Rfsw1

Rs2

Cin1

Cvcc

Cf1

PGOOD

GNDpri

Cin4

Cf3 Cin3

Cf2

Cout2

L6983NQTR

VIN1 1

VINLDO 2

SGND1 3

EN/CLKIN 4

PGOOD 5

VBIAS

FB 7

FSW 8

VCC

SGND2

BOOT

VIN2

EP1-SGND

13 PGND1

SW1

SW2

16 PGND2

Rf2

GND1

Lf2

Rpg2

Cs2

Lf1

Rfsw2

Cin2

VOUT_iso

GND_iso

Rfb1

Cldo

Rpg1

2 1

Csec

Cbs

VOUT1

Ren1

ZB1346-AE

5.6

.10

Cout4

Clkin

Ren2

Cck

Cout1

Rf1

Rldo

Cff

Cs1

Cout3

Figure 8. STEVAL-L6983IV1 circuit schematic (2 of 2) - post regulation (not mounted, bottom side)

Vout_iso

GND_iso

Dz1

Ciso+

U3 LDO40LPU33RY

GND

VIN

VOUT 4

VSENSE 5

ADJ 6

EPAD 7

VISO_gnd

Ciso-

Dz2

VISO+

VISO-

UM3110

Schematic diagrams

UM3110 - Rev 1 page 8/29

7Bill of materials

Table 2. BOM

Item Q.ty Ref. Part/value Description Manufacturer Order code

1 1 U1

L6983IQTR,

QFPN

3X3X0.80 16L

PITCH 0.50

38 V 10 W

synchronous

iso-buck

converter for

isolated

applications

ST L6983IQTR

2 1 U2 SMD 10 pins

EPQ13 Transformer Coilcraft ZB1346-AE

3 1 U3 LDO40LPURY,

DFN6 3x3

400 mA, 38 V

low-dropout

regulator, with

45 µA quiescent

current (not

mounted)

ST LDO40LPURY

4 1 Q1 2STR1215,

SOT-23

Low voltage

fast-switching

NPN power

transistor (not

mounted)

ST 2STR1215

5 1 R1 0603 0.25 SMD resistor

(not mounted) - -

6 1 R2 0603 0.25 SMD resistor

(not mounted) - -

7 1 R3 0603 0.25 SMD resistor

(not mounted) - -

8 1 Rs1 0805 0.25 SMD resistor

(not mounted) - -

9 1 Rb 0Ω 0603 0.25

1% SMD resistor YAGEO RC0603FR-070RL

10 1 Rs2 300Ω 0805 0.25

1% SMD resistor Vishay CRCW0805300RFKEAHP

11 1 Rf1 0603 0.25 SMD resistor

(not mounted) - -

12 1 Rf2 0603 0.25 SMD resistor

(not mounted) - -

13 1 Ren1 100kΩ 0603

0.25 1% SMD resistor YAGEO AC0603FR-07100KL

14 1 Ren2 0603 0.25 SMD resistor

(not mounted) - -

16 1 Rfb1 360kΩ 0603

0.25 1% SMD resistor YAGEO RC0603FR-0775KL

15 1 Rfb2 75kΩ 0603 0.25

1% SMD resistor YAGEO RC0603FR-07360KL

17 1 Rfsw1 0Ω 0603 0.25

1% SMD resistor YAGEO RC0603FR-070RL

18 1 Rfsw2 0603 0.25 SMD resistor

(not mounted) - -

19 1 Rpg2 0603 0.25 SMD resistor

(not mounted) - -

UM3110

Bill of materials

UM3110 - Rev 1 page 9/29

Item Q.ty Ref. Part/value Description Manufacturer Order code

20 1 Rpg1 0603 0.25 SMD resistor

(not mounted) - -

21 1 Rbs 0Ω 0603 0.25

1% SMD resistor YAGEO RC0603FR-070RL

22 1 Rldo 100Ω 0603 0.25

1% SMD resistor YAGEO RC0603FR-10100RL

23 1 C1 0603 MLCC (not

mounted) - -

24 1 Cldo 1uF 0603 50

10% MLCC

Samsung

Electro

Mechanics

CL10A105KB8NNNC

25 1 Cff 0603 MLCC (not

mounted)

26 1 Cb 100nF 0603 50

10% MLCC TDK CGA3E2X7R1H104K080AA

27 1 Cs1 0603 MLCC (not

mounted) - -

28 1 Cin1 10uF 1206 50

10% MLCC

Samsung

Electro

Mechanics

CL31B106KBHNNNE

29 2 Cin2, Cin3 1uF 0805 50

20% MLCC TDK CGA4J3X7R1H105M125AB

30 1 Cin4

100uF

10x10mm 50

20%

Aluminium

Organic

Polymer

Capacitor

KEMET A768MS107M1HLAV024

31 3 Cout1, Cout2,

Cout3

22uF 1206 16

20% MLCC Taiyo Yuden EMK316BB7226ML-T

32 1 Ciso+ 0805 MLCC (not

mounted) - -

33 1 Ciso- 0805 MLCC (not

mounted) - -

34 1 Cs2 180pF 0603 50

1% MLCC Vishay VJ0603A181FXAPW1BC

35 4 Csec, Cf1, Cf2,

Cf3

10uF 1206 50

10% MLCC

Samsung

Electro

Mechanics

CL31B106KBHNNNE

39 1 Cck 0603 MLCC (not

mounted) - -

40 1 Cvcc 1uF 0603 16

10% MLCC TDK CGA3E1X7R1C105K080AC

41 1 Cbs 0603 MLCC (not

mounted) - -

42 1 Cout4 0603 MLCC (not

mounted) - -

43 1 Lf1 220Ω 0805 3

25% Ferrite bead TDK MPZ2012S221ATD25

44 1 Lf2 6.8uH 4x4mm

3.9 20% Inductor Coilcraft XGL4030-682MEC

45 1 D1 STPS1170AF,

SMA Flat

170 V, 1 A

power Schottky

rectifier

ST STPS1170AF

UM3110

Bill of materials

UM3110 - Rev 1 page 10/29

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