ILC6363

PRODUCT SPECIFICATION

6

REV. 1.3.5 5/21/02

Figure 5. PFM Waveform

Other Considerations

The other limitation of PWM techniques is that, while the

fundamental switching frequency is easier to filter out since

it's constant, the higher order harmonics of PWM will be

present and may have to be filtered out, as well. Any filtering

requirements, though, will vary by application and by actual

system design and layout, so generalizations in this area are

difficult, at best.

However, PWM control for boost DC-DC conversion is

widely used, especially in audio-noise sensitive applications

or applications requiring strict filtering of the high frequency

components.

Low Battery Detector

The ILC6363's low battery detector is a based on a CMOS

comparator. The negative input of the comparator is tied to

input is the LBI/SD pin. It uses a simple potential divider

arrangement with two resistors to set the LBI threshold as

shown in Figure 6. The input bias current of the LBI pin is

only 200nA. This means that the resistor values R1 and R2

can be set quite high. The formula for setting the LBI

threshold is:

VLBI = VREF x (1+R5/R6)

Since the LBI input current is negligible (<200nA), this

equation is derived by applying voltage divider formula

across R6. A typical value for R6 is 100k

Ω.

R5 = 100k

Ω x [(VLBI/VREF) -1],

where VREF=1.25V (nom.)

The LBI detector has a built in delay of 120ms. In order to

get a valid low-battery-output (LBO) signal, the input volt-

age must be lower than the low-battery-input (LBI) threshold

for a duration greater than the low battery hold time

ing due to voltage transients at the battery terminal caused by

high frequency switching currents.

Figure 6. Low Battery Detector

The output of the low battery detector is an open drain

capable of sinking 2mA. A 10k

Ω pull-up resistor is

recommended on this output.

The low battery detector can also be configured for voltages

circuitry for this is shown in Figure 7.

1.25V:

This equation can also be derived using voltage divider

formula across R2. A typical value for R2 is 100k

Ω.

Shut Down

The LBI pin is shared with the shutdown pin. A low voltage

(<0.4V) will put the ILC6363 into a power down state. The

simplest way to implement this is with an FET across R6 as

shown in Figure 8. Note that when the device is not in PWM

mode or is in shutdown the low battery detector does not

operate.

Switch Waveform

R6

R5

LBI/SD

3

ILC6363

Shutdown

DELAY

100ms

1.25V

Internal

Reference

GND

7

LBO

3.3V

6

+

-

8

R2

3

LBI/SD

R1

ILC6363

+

-

1.25V

Internal

Reference

GND

7