IW3614 datasheet(13/18 Pages) DIALOG

13 / 18 page

Rev. 0.7

iW3614

Page 13

PReliminaRy

iW3614

AC/DC Digital Power Controller for

High Power Factor Dimmable LED Drivers

9.11 PCL, OC and SRS Protection

Peak-current limit (PCL), over-current protection (OCP) and

sense-resistor short protection (SRSP) are features built-

in to the iW3614. With the I

SENSE pin the iW3614 is able to

monitor the primary peak current. This allows for cycle by

cycle peak current control and limit. When the primary peak

current multiplied by the I

SENSE sense resistor is greater than

OCP over-current protection engages and the IC immediately

turns off the gate drive until the next cycle. The output driver

continues to send out switching pulses, but the IC will

immediately turn off the gate drive if the OCP threshold is

reached again.

If the I

SENSE sense resistor is shorted there is a potential

danger of the over-current condition not being detected.

Thus the IC is designed to detect this sense-resistor-short

fault after the start-up, and shutdown immediately. The V

will be discharged since the IC remains biased. In order

to prevent overcharging the output voltage, the iW3614

employs an extended discharge time before restart, similar

to the discharge time described in section 9.10.

9.12 Over Temperature Protection

If an NTC thermistor is connected from the V

T pin to GND

then, the iW3614 is able to detect and protect against an

over temperature event (OTP).

The iW3614 provides a current (I

VT) to the VT pin and detects

the voltage on the pin. Based on this voltage the iW3614

can monitor the temperature on the NTC thermistor. As the

T pin voltage reduces, the iW3614 reduces the amount of

chopping and the output current according to Figure 9.12.

There is a hysteresis of 84 mV on V

T pin voltage for each

power limiting step.

VT Pin Voltage

0.0

0.2

0.4

0.6

0.8

1.0

100

VT Pin Voltage

0.0

0.2

0.4

0.6

0.8

1.0

100

a) V

T from 1.0 V to 0.0 V

b) V

T from 0.0 V to 1.0 V

Figure 9.12 : V

T Pin Voltage vs. % of Nominal Output Current

T from 1.0V to 0.0V

VT Pin Voltage

0.0

0.2

0.4

0.6

0.8

1.0

100

Figure 9.13 : V

T Pin Voltage vs. % of Nominal Output Current

T from 0.0V to 1.0V

When the V

T pin voltage reaches VP-LIM(HI) the output current

begins to reduce as shown in Figure 9.12. At V

P-LIM(LO) the

output current reduces to 1%. The device can be placed

in shutdown mode by pulling the V

T pin to ground or below

SH-TH.

9.13 Thermal Design

The iW3614 is typically installed inside a small enclosure,

where space and air volumes are constrained. Under these

circumstances θ

JA (thermal resistance, junction to ambient)

measurements do not provide useful information for this

type of application. Instead we have provided ψ

JB which

estimates the increase in die junction temperature relative to

the PCB surface temperature. Figure 9.14 shows the PCB

surface temperature is measured at the IC’s GND pin pad.

GND pin

Thermal Vias

Connect top thermal pad

to bottom copper

Thermal Epoxy

Artic Silver

IC Die

Printed Circuit Board

Exposed

Die Pad

Copper Thermal Pad

Under Package

Printed Circuit Board

PCB Top Copper Trace

PCB Bottom Copper Trace

Figure 9.14 : Ways to Improve Thermal Resistance

Using ψ

JB the junction temperature (TJ) of the IC can be

found using the equation below.

⋅ψ

(9.13)

where, T

B is the PCB surface temperature and PH is the

power applied to the chip or the product of V

CC and ICCQ.

IW3614 Datasheet(PDF) 13 Page - Dialog Semiconductor

IW3614 Datasheet(HTML) 13 Page - Dialog Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Datasheet Download

Link URL