LNK6404 Ver la hoja de datos (PDF) - Unspecified

Número de pieza

componentes Descripción

Fabricante

LNK6404

Energy-Efficient, Accurate Primary-Side Regulation CV/CC Switcher for Adapters and Chargers

Unspecified 

LNK64x4-64x8

Key Application Considerations

Output Power Table

The data sheet maximum output power table (Table 1) repre- sents

the maximum practical continuous output power level that can be

obtained under the following assumed conditions:

1. Assumes minimum input DC voltage >90 VDC, KP ≥1 (Recom-

mend KP ≥1.15 for accurate CC regulation), η >78%, DMAX <55%.

2. Output power capability is reduced if a lower input voltage

is used.

3. Minimum continuous power with adequate heat sink measured at

50 °C ambient with device junction below

110 °C.

4. Assumes bias winding is used to supply BYPASS pin.

Output Tolerance

LinkSwitch-3 provides an overall output tolerance (including

line, component variation and temperature) of ±5% for the output

voltage in CV operation and ±10% for the output current during CC

operation over a junction temperature range of 0 °C to 110 °C.

BYPASS Pin Capacitor Selection

A 1 mF BYPASS pin capacitor is recommended. The capacitor

voltage rating should be greater than 7 V. The capacitor’s dielectric

material is not important but tolerance of capacitor should be ≤

±50%. The capacitor must be physically located adjacent to the

LinkSwitch-3 BYPASS pin.

Cable Drop Compensation

The amount of output cable compensation is determined by the third

digit in the device part number. Table 2 shows the amount of

compensation for each LinkSwitch-3 device.

The output voltage that is entered into PIXls design spreadsheet is

the voltage at the end of the output cable when the power supply is

delivering maximum power. The output voltage at the terminals of

the supply is the value measured at the end of the cable multiplied by

the output voltage change factor.

LinkSwitch-3 Output Cable Voltage

Drop Compensation

Device

Output Voltage Change Factor (±1%)

LNK640x

1.02

LNK641x

1.04

LNK642x

1.06

LNK643x

1.08

LNK644x

1.01

Table 2. Cable Compensation Change Factor vs. Device.

LinkSwitch-3 Layout Considerations

Circuit Board Layout

LinkSwitch-3 is a highly integrated power supply solution that

integrates on a single die, both, the controller and the high- voltage

MOSFET. The presence of high switching currents and voltages

together with analog signals makes it especially important to follow

good PCB design practice to ensure stable and trouble free operation

of the power supply. See Figure 5 for a recommended circuit board

layout for LinkSwitch-3.

When designing a printed circuit board for the LinkSwitch-3 based

power supply, it is important to follow the following guidelines:

Single Point Grounding

Use a single point (Kelvin) connection at the negative terminal of the

input filter capacitor for the LinkSwitch-3 SOURCE pin and bias

winding return. This improves surge capabilities by returning surge

currents from the bias winding directly to the input filter capacitor.

Bypass Capacitor

The BYPASS pin capacitor should be located as close as possible to

the SOURCE and BYPASS pins.

Feedback Resistors

Place the feedback resistors directly at the FEEDBACK pin of the

LinkSwitch-3 device. This minimizes noise coupling.

Thermal Considerations

The copper area connected to the SOURCE pins provides the

LinkSwitch-3 heat sink. A good estimate is that the LinkSwitch-3 will

dissipate 10% of the output power. Provide enough copper area to

keep the SOURCE pin temperature below 110 °C is recommended to

provide margin for part to part RDS(ON) variation.

Secondary Loop Area

To minimize leakage inductance and EMI the area of the loop connecting

the secondary winding, the output diode and the output filter capacitor

should be minimized. In addition, sufficient copper area should be

provided at the anode and cathode terminal of the diode for heat

sinking. A larger area is preferred at the quiet cathode terminal.

A large anode area can increase high frequency radiated EMI.

Electrostatic Discharge Spark Gap

A spark gap is created between the output and the AC input. The

spark gap directs ESD energy from the secondary back to the AC

input. The trace from the AC input to the spark gap electrode should

be spaced away from other traces to prevent unwanted arcing

occurring and possible circuit damage.

Drain Clamp Optimization

LinkSwitch-3 senses the feedback winding on the primary-side to

regulate the output. The voltage that appears on the feedback

winding is a reflection of the secondary winding voltage while the

internal MOSFET is off. Therefore any leakage inductance induced

ringing can affect output regulation. Optimizing the drain clamp to

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5

Rev. C 03/16

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