LNK6666V datasheet(4/24 Pages) POWERINT

4 / 24 page

Rev. E 06/15

LinkSwitch-HP

www.power.com

Auto-Restart

In the event of an open-loop fault (no connection between the

feedback winding and the feedback divider network or the

FEEDBACK pin to the feedback network), the sensed current

out of FEEDBACK pin will be zero during MOSFET on-time, the

device enters into line brown-out protection (line UV). In the

event of output short-circuit or overload condition, the device

enters into auto-restart mode. Auto-restart minimizes the

power dissipation under fault conditions, the device will turn on

and off at duty cycle of typically 3% as long as the fault condition

persists. In auto-restart switching is disabled for t

AR(OFF)1

(typ. 150 ms) when the FEEDBACK pin voltage has dropped

below the auto-restart threshold V

FB(AR) for the shutdown default

delay time t

AR(ON) (typ. 35 ms). After this period switching is

enabled again with the device entering soft-start (typ. 15 ms).

For the first auto-restart off-period switching is disabled for a

reduced time t

AR(OFF)2 (typ. 1500 ms) to reduce the power supply

restart time during line cycling. Optionally the default shutdown

delay time can be extended by adding a capacitor to the

PROGRAM pin.

Hysteretic Thermal Shutdown

The thermal shutdown circuitry senses the controller die

temperature. The threshold is set at 142

°C with a 75 °C

hysteresis (both typical). Once the device temperature rises

above 142

°C, the power MOSFET is disabled and remains

disabled until the die temperature falls by 75

°C, at which point

the device is re-enabled. The large hysteresis maintain the

average temperature below the temperature rating of low cost

CEM type PCB material in most cases.

Safe Operating Area (SOA) Protection

The device features a safe operating area (SOA) protection

mode which disables MOSFET switching for 4 consecutive

cycles in the event the peak switching current reaches the

current limit in less than time t

ON(SOA). This prevents excessive

drain currents during start-up and output short-circuit conditions

by providing additional time for the primary inductance to reset.

The SOA protection is disabled when the output voltage is

within 7.5% of regulation voltage.

Sample and Hold (S/H)

The sample and hold block senses the output voltage at auxiliary

winding during secondary rectifier on-time. The FEEDBACK pin

voltage is sampled after the turn-off of the internal switch to

compensate for diode conduction time differences. Sampling

time increases monotonically from 1.2

ms at no or light load to

2.5

ms at full load. Sampled voltage is held until the next clock

cycle. The output of S/H is fed to the error amplifier, once in

regulation the sampled voltage is 2 V.

BYPASS (BP) Programming

This feature selects either hysteretic or latching OVP/OCP and

OTP protection based on capacitor loading on the BYPASS pin.

The shutdown type is determined at the device power-up as

shown in Table 3.

Current Limit Setting

During power-up the cycle-by-cycle current limit is determined

by measuring the resistor value connected to the PROGRAM

pin by the measurement is performed by applying 1.25 V (see

Figure 10). The current limit can be set between 40% to 100%

in steps of 10% as shown in Table 4. After the current limit is

set the PROGRAM pin voltage is reduced to ~0 in order to

minimize power dissipation.

Programmable Shutdown Delay

The default auto-restart shutdown delay time t

SD(AR) (typ. 35 ms)

can optionally be extended by connecting a capacitor to the

PROGRAM pin. Once a lost regulation fault is detected the

PROGRAM pin voltage is cycled 128 times between V

PD(DL)

(typ. 0.5 V) and V

PD(DU) (typ. 1.2 V) as shown in Figure 10.

Figure 6 depicts the relationship between extended shutdown

delay time, added PROGRAM pin capacitor and current limit

programming resistor.

Figure 5.

Compensation Pin Characteristics (Multi-Mode Operation).

fSW(LF)

VC(MAX)

VC(MIN) VC(MCM)

132

100%

50%

25%

PI-6722-111212

Compensation

Voltage (

∝ POUT)

Compensation

Voltage (

∝ POUT)

LIMIT(NORM)

124

100

23.2

78.7

15.0

52.3

125

10.0

34.8

Table 4.

Current Limit Selection vs. Program Pin Resistor Value.

0.47

4.7

OVP

Latching

Auto-Restart

Latching

Lost Regulation

(SC, OC)

Auto-Restart Auto-Restart

Latching

OTP

Latching

Hysteretic

Latching

Table 3.

Shutdown Type vs. Value of BYPASS Pin Capacitance.

LNK6666V Datasheet(PDF) 4 Page - Power Integrations, Inc.

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