ZL2008 datasheet(43/47 Pages) INTERSIL

43 / 47 page

ZL2008

Data Sheet Revision 2/19/2009

www.intersil.com

7.5 Phase Enable (PH_EN Pin)

Phase enable is used to dynamically add or drop a

current sharing phase during operation. Set the PH_EN

pin high to enable a phase and low to disable a phase

(open is an invalid state). The PH_EN pin replaces the

PHASE_CONTROL command.

For proper operation, the pin must be externally driven

high or low without switching glitches. Also, ensure

phase enable is high for the reference and member

devices of a current sharing group prior to ramp-up.

7.6 MFR_CONFIG Command

Application

specific

values

are

set

the

MFR_CONFIG command. The following parameters

must be set to properly configure current sharing.

a. Current Sense Blanking Delay (bits 15:11) –

The current sense delay parameter controls the

blanking time when no current measurement is

taken. This allows the filtering of noise from

the current measurement circuit when the FETs

are switching. The actual value selected

depends on fSW, sensing method and ring-out

duration. The same delay is used for both

reference and member devices.

b. Current Sense Control (bits 5:4) – Three

modes of current sensing are available

depending on duty cycle and switching

frequency as listed in Table 38. (Also refer to

Section

5.9,

“Current

Limit

Threshold

Selection,”). The same sensing is used for both

reference and member devices.

Note, the following parameters are automatically set

when current sharing is enabled.

c. Alternate

Ramp

Control

(bit

–

Automatically set to “1” (enabled) for both

reference and member devices when current

sharing is enabled.

d. SYNC Pin Output Control (bit 0) –

Automatically set to push-pull for a SYNC

clock output and open-drain for a SYNC clock

input.

Table 38. Current Sense Options

Current Sense Configuration

Usage

Ground referenced, down slope

(RDSON sensing)

Low duty cycle

and low fSW

Vout referenced, down slope

(Inductor DCR sensing)

Low duty cycle

and high fSW

Vout referenced, up slope

(Inductor DCR sensing)

High duty cycle

7.7 VOUT_DROOP Command

The droop or load-line resistance is used as part of the

current sharing algorithm. When current sharing is

enabled, VOUT_DROOP is automatically set to a

value of 0xBA80 (1.25 mΩ). The same droop value is

used for both reference and member devices.

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