10

FN7102.5

December 1, 2004

It also allows 100% turn-on of the upper PMOS switch,

is the PMOS on-resistance, nominally 30m

Ω at room

temperature with a temperature coefficient of 0.2m

Ω/°C.

OUTPUT VOLTAGE SELECTION

The output voltage can be as high as the input voltage minus

the PMOS and inductor voltage drops (as seen previously in

Equation 2). Referring to the Typical Application Circuit on

the following formula:

It is important that the series combination of R1 and R2 is

large enough as to not draw excessive current from the

output.

VOLTAGE MARGINING

The EL7566 has built-in 5% load stress test (commonly

called voltage margining) function. Combinations of TM and

SEL set the margins shown in Table 2. When this function is

not used, both pins should be connected to SGND, either

directly or through a 10k

Ω resister. Figure 16 shows this

feature.

SWITCHING FREQUENCY

The regulator has a programmable switching frequency of

200kHz to 1MHz. The switching frequency is generated by a

relaxation comparator and adjusted by a capacitor from the

duty ratio and runs from 0.2V to 1.2V. Refer to the curve in

frequency. If external synchronization is desired, the circuit

in Figure 21 can be used.

Always choose the converter self-switching frequency 20%

lower than the sync frequency to accommodate component

variations.

Protection Features

The EL7566 features a wide range of protective measures to

prevent the persistence of damaging system conditions.

These features are overvoltage, overcurrent, Power-On-

Reset (POR), and Thermal Shutdown protection.

OVERVOLTAGE PROTECTION (OVP)

The EL7566 monitors the output voltage and will shut down

if it exceeds 110% of the set regulation point. This is

accomplished by comparing the reference to the FB pin

voltage. If an overvoltage condition is met, the controller will

turn the high-side switch off, the low-side switch on, and pull

PGOOD low. The converter will not latch off and will proceed

with a soft-start as soon as the fault condition is cleared.

OVERCURRENT PROTECTION (OCP)

The current information for PWM ramp generation is also

used for overcurrent protection. The measured current is

compared against a preset Overcurrent threshold (~7-10A).

If the output current exceeds the threshold, the output will

shut down by turning off the high-side switch and turning the

low-side switch on. This event, like OVP, will not latch the

converter off. A soft-start will be initiated when the fault is

cleared.

POWER-ON RESET (POR)

To ensure proper regulator operation, a power-on reset

feature monitors the input voltage. When adequate input

shut down in the same manner as OVP or OCP.

THERMAL PROTECTION AND JUNCTION

TEMPERATURE INDICATOR

An internal temperature sensor continuously monitors the

junction temperature. If the junction temperature exceeds

135°C, the regulator is in a fault condition and will shut

down. When the temperature falls back below 110°C, the

regulator goes through the soft-start procedure again.

TABLE 1.

0.8

2

Open

12.49

10

1.2

4.99

10

1.5

10

11.5

1.8

12.7

10.2

2.5

21.5

10

3.3

36

11.5

TABLE 2.

CONDITION

TM

SEL

Normal

0

X

Nominal

High Margin

1

1

Nominal + 5%

Low Margin

1

0

Nominal - 5%

V

O

V

IN

R

L

R

DSON1

+

() I

O

×

–

=

V

O

0.8

1

R

1

R

2

-------

+







×

=

EL7566

100pF

EXTERNAL SYNC

SOURCE

FIGURE 20. EXTERNAL SYNC CIRCUIT

EL7566