CAT3604V

http://onsemi.com

11

device runs diagnostics and goes to 1x mode where the

output is basically equal to the input voltage.

As soon as the output exceeds about 6 V, the driver resets

itself and reevaluate the mode.

If the die temperature reaches +150

°C, the device enters

a thermal protection shutdown mode. When the device

temperature drops to about +130

°C, the device resumes

normal operation.

LED Selection

recommended in order to extend battery life and keep the

driver in 1x mode longer as the battery voltage decreases.

supply voltage of 0.2 V.

External Components

The driver requires four external 1

mF ceramic capacitors

for decoupling input, output, and for the charge pump. Both

capacitors type X5R and X7R are recommended for the

LED driver application. In all charge pump modes, the input

current ripple is kept very low by design and an input bypass

capacitor of 1

mF is sufficient.

In 1x mode, the device operates in linear mode and does

not introduce switching noise back onto the supply.

Recommended Layout

In charge pump mode, the driver switches internally at a

high frequency. It is recommended to minimize trace length

to all four capacitors. A ground plane should cover the area

under the driver IC as well as the bypass capacitors. Short

implemented with the use of multiple via. A copper area

matching the TQFN exposed pad (TAB) must be connected

to the ground plane underneath. The use of multiple via

improves the package heat dissipation.

Figure 27. PCB Layout

PWM Dimming

The EN pin is used to provide total Shutdown of the device

as well as High Resolution PWM dimming control on the

LED Channels.

Shutdown of the device occurs after the EN pin has been

held low for 1.5 ms. During the “soft−start” power−up

sequence from the shutdown mode, the LED current

typically settles within 40

ms (for 1X mode operation). This

LED current settling time becomes 400

ms if 1.33X

operation is needed (i.e low battery voltage).

For High Resolution PWM dimming control (typically

frequencies at 2 kHz or above), the device will remain

powered and only the LED channels output will be switched

on and off during the PWM (the rest of the device will

remain powered−up). This allows the output channels to

have “instant−on” response, where the LED current settles

within 1

ms of the applied PWM dimming signals. This

“instant−on” modes makes the device suitable for extremely

high frequency PWM dimming schemes.

Figure 28 shows the output current for PWM frequencies

up to 100 kHz and with duty cycles of 30% and 70%.

Figure 28. Output Current vs. PWM Frequency

10

20

30

40

50

60

70

80

90

100

0.1

1

10

100

PWM FREQUENCY (kHz)

70% DC

30% DC

should meet the following timing limits: