IW3602 datasheet(13/19 Pages) DIALOG

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iW3602

AC/DC Digital Power Controller for

Dimmable LED Drivers

Rev. 1.0

iW3602

Datasheet

13 of 19

below the UVLO threshold, the controller resets itself and

then initiates a new soft-start cycle.

Under a fault condition, the controller tries to start-up for

three consecutive times. If all three start-up attempts fail,

the controller enters an inactive mode, during which the

controller does not respond to VCC power-on requests. The

controller is activated again after it sees 29 start-up attempts.

The controller can also be reset to the initial condition if VCC

is discharged. Typically, this extended discharge time is

around 3 to 5 seconds.

This extended discharge time allows the iW3602 to support

hot-plug LED modules without causing dangerously high

output voltages while maintaining a quick recovery.

9.11 PCL, OC and SRS Protection

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

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

into the iW3602. With the ISENSE pin the iW3602 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 ISENSE sense resistor is greater

than VOCP over-current protection is engaged and the IC

immediately turns off the gate drive until the next cycle. The

output driver continues to send out switching pulses; the IC

immediately turns off the gate drive if the OCP threshold is

reached again.

If the ISENSE 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 shut down immediately. The

VCC is discharged since the IC remains biased. In order

to prevent overcharging the output voltage, the iW3602

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 VT pin to GND

then, the iW3602 is able to detect and protect against an

over temperature event (OTP).

The iW3602 provides a current (IVT) to the VT pin and detects

the voltage on the pin. Based on this voltage the iW3602

can monitor the temperature on the NTC thermistor. As the

VT pin voltage reduces, the iW3602 reduces the amount of

chopping and the output current according to Figure 9.12.

There is a hysteresis of 84mV on VT 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 : VT Pin Voltage vs. % of Nominal Output Current

VT 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 : VT Pin Voltage vs. % of Nominal Output Current

VT from 0.0V to 1.0V

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

begins to reduce as shown in Figure 9.12. At VP-LIM(LO) the

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

shutdown mode by pulling the VT pin to ground or below

VSH-TH.

9.13 Thermal Design

Note: This section only applies to iW3602-01 and -03.

The iW3602 is typically installed inside a small enclosure,

where space and air volumes are constrained. Under these

circumstances θJA (thermal resistance, junction to ambient)

measurements do not provide useful information for this

type of application. Instead we have provided ψJB 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.

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