Rev. B 04/15

19

TFS7701-7708

www.power.com

Figure 20. Recommended Y Capacitor Connections to Improve Surge and ESD Immunity and Output Ripple High-Frequency Noise.

Figure 21. Close-up of Output Ripple Voltage Showing Large Spikes. These

Spikes are Often Caused by Common-Mode Switching Noise

Appearing in the Output. A Poor Secondary Layout or a Y Capacitor

Connected to the Output Connector Instead of to the Transformer

Secondary GROUND Pin, can Cause the Spikes.

PI-7011-052913

S

HiperTFS-2

HD

Bulk

Capacitor

Y

Capacitor

Not

Recommended

Bad

Good

Best

Bad

STANDBY DRAIN, MAIN DRAIN, HIGH-SIDE SOURCE, and

HIGH-SIDE OPERATING VOLTAGE Pins

The STANDBY DRAIN, MAIN DRAIN, HIGH-SIDE SOURCE, and

HIGH-SIDE OPERATING VOLTAGE pins are high-voltage switching

nodes with high dv/dt and must be kept away from the traces

connected to low voltage small signal pins (i.e., LINE-SENSE,

RESET, FEEDBACK, ENABLE pins). Stray capacitance between

them will cause capacitive noise injection. The small components

connected to the HIGH-SIDE OPERATING VOLTAGE pin also

have high dv/dt with respect to the other small signal traces.

Place them close to the HIGH-SIDE OPERATING VOLTAGE pin

and away from the other small signal traces. Also place the

Figure 22. VDDH Components Exhibit Large dv/dt and Should be Mounted Close

to the HIGH-SIDE SOURCE and VDDH pins. The Diode Should be

Mounted Close to the VDDH Pin so that the Cathode Trace can be

Made Short. The Anode Trace is Connected to V

AUX and is Quiet.

HD

HS

HiperTFS-2 VDDH

CONTROL

PI-7020-051713

C1

Cathode Close

to C2

Place all These

Components

Close to

VDDH, HS

*R1

VIN

*C2

VHIGH_BIAS

PI-7000-052113

Large Spikes Caused by

Incorrect Y Capacitor

Secondary Location

Normal

Switching Ripple

bootstrap diode (if used, required for 132 kHz), close to the

HIGH-SIDE OPERATING VOLTAGE pin.

LINE-SENSE and RESET

Care must be taken to avoid noise injection into the LINE-SENSE

and RESET pins. These pins have multiple series resistors in

order to reduce the voltage stress per resistor. See Figure 23.

The series resistors in each chain do not have to be the same

type or value. If they have different maximum voltage ratings,

they should have different values, proportional to their voltage

ratings. If the resistors are different types with different

withstand voltage ratings, (e.g., 0805 SMD for R25 and R36,