ISL8200MM

FN7690 Rev 2.00

Page 17 of 24

Mar 15, 2013

Multi-module operation can be achieved by connecting the

ISHARE pin of two or more modules together. In multi-module

operation the voltage on the ISHARE pin correlates to the

average current of all the active channels. The output current of

each module in multi-module operation is compared to a precise

1.2V threshold to determine the overcurrent condition.

Additionally, each module has an overcurrent trip point of 108μA

with 7-cycle delay. This scheme helps protect from damaging a

module(s) in multi-module mode by not having a single module

carrying more than 108μA. Note that it is not necessary for the

RISHARE to be scaled to trip at the same level as the 108μA OCP

comparator. Typically the ISHARE pin average current protection

level should be higher than the phase current protection level. For

instance, when Channel 1 operates independently, the OC trip set

by 1.2V comparator can be lower than 108μA trip point as shown

in Equation 6.

where NCNTL is the number of the ISL8200MMREP modules in

parallel or multi-module operations; ITRIP = 108μA; IOC is the

load overcurrent trip point; TMIN_OFF is the minimum UGATE turn

off time that is 350ns; RISHARE in Equation 7 represents the total

equivalent resistance in ISHARE pin bus of all ICs in multiphase

or module parallel operation.

ISL8200MMREP has a low-side FET with typical rDS(ON) of 9mΩ

(VGS = 10V, IDS = 30A).

Note: ISL8200MMREP has integrated 2.2kΩ resistance (RSEN-IN).

Therefore, the equivalent resistance of RSEN is:

The OC trip point varies in a system mainly due to the MOSFET

rDS(ON) variations (overprocess, current and temperature). To

avoid overcurrent tripping in the normal operating load range,

find the RSEN resistor from Equation 8 of IPEAK with:

1. The maximum rDS(ON) at the highest junction temperature

2. The minimum ISOURCE from the “Electrical Specifications”

table on page 8.

3. Determine IOC for:

where

IL is the output inductor ripple current.

The relationships between the external RSEN-EX values and the

typical output current IOUT(MAX) OCP levels for ISL8200MMREP

are shown in Table 2:

In a high input voltage, high output voltage application, such as

20V input to 5V output, the inductor ripple becomes excessive

due to the fix internal inductor value. In such application, the

output current will be limited from the rating to approximately

70% of the module’s rated current.

When OCP is triggered, the controller pulls EN low immediately to

turn off UGATE and LGATE.

For overload and hard short condition, the overcurrent protection

reduces the regulator RMS output current much less than full

load by putting the controller into hiccup mode. A delay time,

equal to 3 soft-start intervals, is entered to allow the disturbance

to be cleared out. After the delay time, the controller then

initiates a soft-start interval. If the output voltage comes up and

returns to the regulation, PGOOD transitions high. If the OC trip is

exceeded during the soft-start interval, the controller pulls EN low

again. The PGOOD signal will remain low and the soft-start

interval will be allowed to expire. Another soft-start interval will

be initiated after the delay interval. If an overcurrent trip occurs

again, this same cycle repeats until the fault is removed.

Oscillator

The Oscillator is a sawtooth waveform, providing for leading edge

modulation with 350ns minimum dead time. The oscillator

(Sawtooth) waveform has a DC offset of 1.0V. Each channel’s

peak-to-peak of the ramp amplitude is set proportionally to the

voltage applied to its corresponding FF pin.

Frequency Synchronization and Phase Lock

Loop

The FSYNC_IN pin has two primary capabilities: fixed frequency

operation and synchronized frequency operation. By tying a

resistor (RFS) to PGND1 from the FSYNC_IN pin, the switching

frequency can be set at any frequency between 700kHz and

1.5MHz. The ISL8200MMREP has an integrated 59kΩ resistor

between FSYNC_IN and PGND1, which sets the default frequency

to 700kHz. The frequency setting curve shown in Figure 27 is

provided to assist in selecting an externally connected resistor

RFS-ext between FSYNC_IN and PGND1 to increase the switching

frequency.

RISEN1

IOC

VOUT

L

----------------

1D

–

2FSW

---------------- TMIN_OFF

–







+







RDS



ITRIP

------------------------------------------------------------------------------------------------------------------------

=

RISHARE

1.2V

ITRIP

---------------

=

RISET

RISHARE NCNTL



=

(EQ. 6)

RSEN

RSEN-EX RSEN-IN



RSEN-EX RSEN-IN

+

--------------------------------------------------------

=

(EQ. 7)

IOC IOUT MAX



IL



2

-------------

+



(EQ. 8)

TABLE 2.

RSEN-EX

OCP (A) @

VIN = 12V

OPEN

17

50kΩ

15.5

20kΩ

14.5

10kΩ

14

5kΩ

12.5

3kΩ

11

2kΩ

8