Texas Instruments SN6507DGQEVM User Manual Download Page 6

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• RDC is used for duty cycle control programming and is active when pins 2-3 of J13 are connected. If duty

cycle control is used, ensure a compatible transformer is placed in footprint T1 and output inductors with
sufficient inductance are populated in place of L1 (and L2 as needed)

• RCLK can be used to program the internal CLK and is active when pins 3-4 of J10 are connected
• RSR is used to adjust the slew rate of the switching pins, SW1 and SW2, and is active when pins 2-3 of J9

are connected

• Rilim is used to adjust the over-current protection limit of SN6507
• Css is used to adjust the soft start time of SN6507 during power-up

Transformer replacement:

A 24 V IN to 15 V OUT transformer is included by default in place of T1. To evaluate

different transformers, de-solder this transformer and replace it with a 6-pin or 8-pin push-pull transformer that is
compatible with the T1 footprint.

Secondary-side snubber circuit:

An RC snubber circuit of 100 Ω, 62pF is populated on R12, C15 and R13,

C16 by default to help minimize electromagnetic emissions. These components are optional, so they may be
replaced with other components or removed from the EVM and excluded from designs using the SN6507 device.

Primary-side snubber circuits:

Primary-side snubber circuits can be placed using footprints for R10, C11 and

R11, C12 to further reduce emissions. Primary-side snubber circuit values can be calculated using the steps in

How to Reduce Emissions in Push-Pull Isolated Power Supplies (SLLA566)

Output rectifier:

Diode placeholders D1, D2, D4, D5, and resistor R9 are included to allow system designers to

experiment with the different output topologies push-pull power supplies can support. D2 and D5 are populated
by default as this is the typical application topology, and some example output designs found in the SN6507 data
sheet can be configured on this EVM to achieve bi-polar or voltage-doubling outputs using the “-Vout” net by
populating D1 and D4 on the EVM. Make sure the output LDO, U1, is bypassed by disconnecting pins 1-2 of J4
if R9 is removed since the ISO_GND potential will be floating.

Ferrite bead options:

To reduce emissions when power supply outputs are connected to long cables or have

high ringing, ferrites can be soldered in place of R15, R14, R6, R7, and R8. A ferrite with 1 kΩ impedance or
greater at 100 MHz like the Würth Elektroniks 742792662 is recommended.

Input-side transient protection:

Provisions for a flat-clamp diode like TVS3300, U3, or a TVS diode like

SMAJ36A, D7, are included to protect the power supply input from external transients above the desired power
supply level.

Output-side transient protections:

TVS diode placeholders D3 and D6 are included to protect the SN6507

output from external transients above the desired output power supply level.

LDO output:

The included

LM317A

can be configured to change the regulated output voltage level by

connecting either of the R5x resistors using jumper J3. When configuring the LDO, ensure the LDO input voltage
is within the LDO’s recommended limits and high enough to support the desired output voltage level and the
dropout voltage of the LM317A. A regulated 15 V output can be configured by connecting pins 1-2 of J3, a
regulated 12 V output can be configured by connecting pins 2-3 of J3, or a custom output voltage value can be
configured by connecting pins 5-6 of J3 and changing R5C to a value which meets the desired output voltage
using

Equation 1

OUT

= 1.25 V x (1+R5C/R4) + (50 uA x R5C)

(1)

A table of calculated resistor values for R5C to achieve common voltage outputs is shown

Table 4-1

Table 4-1. LM317A (U1) Resistor Values for Common Regulated Output Voltages

Desired V

OUT

(V)

R4 value (Ω)

R5C value (Ω)