ISL68201 Datasheet, PDF(12/32 Page) Intersil Corporation – Single-Phase R4 Digital Hybrid PWM Controller

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ISL68201 Datasheet, PDF (12/32 Pages) Intersil Corporation – Single-Phase R4 Digital Hybrid PWM Controller

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ISL68201

TABLE 6. PROG 4 RESISTOR READER EXAMPLE (Continued)

9Fh

75 Open

0.078

800

BFh

105 Open

0.157

800

DFh

147 Open

0.315

800

FFh

499 Open

0.625

800

Soft-Start

The ISL68201 based regulator has 4 periods during soft-start, as

shown in Figure 7 on page 12. After a 5.5ms timeout (worst

case = 6.5ms) of bias supplies, as shown in Figures 21 and 22 on

page 22, once the EN pin reaches above its enable threshold, the

controller begins the first soft-start ramp after a fixed soft-start

delay period tD1. The output voltage reaches the boot-up voltage

(VBOOT) at a fixed slew rate in period tD2. Then, the controller will

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command is valid, the ISL68201 will initiate the ramp until the

voltage reaches the new VOUT_COMMAND voltage in period tD4.

The soft-start time is the sum of the 4 periods, as shown in

Equation 1.

tSS = tD1 + tD2 + tD3 + tD4

(EQ. 1)

tD1 is a fixed delay with the typical value as 200Âµs. tD3 is

determined by the time to obtain a new valid VOUT_COMMAND

voltage from SMBus/PMBus/I2C bus. If the VOUT_COMMAND is

valid before the output reaches the boot-up voltage, the output will

turn around to respond to the new VOUT_COMMAND code.

VBOOT< PRE-CHARGED < OVP

VBOOT

PRE-CHARGED<VBOOT

VOUT

tD1

tD2

tD3 tD4

PGOOD

FIGURE 7. SOFT-START WAVEFORMS

During tD2 and tD4, ISL68201 digitally controls the DAC voltage

change. The ramp time tD2 and tD4 can be calculated based on

Equations 2 and 3, once the slew rate is set by the PROG4 pin.

tD2 = R-----A-----VM----B-P---O--_--O-R----TA----T----E-- ï¨ïsï©

(EQ. 2)

tD4 = V--R---O--A--U---M-T----P-â----_-V--R--B--A--O--T--O--E---T- ï¨ïsï©

(EQ. 3)

The ISL68201 supports precharged start-up, it initiates the first

PWM pulse until the internal reference (DAC) reaches the

precharged level at RAMP_RATE, programmed by PROG4 or

D5[2:0]. When the precharged level is below VBOOT, the output

walks up to the VBOOT at RAMP_RATE and releases PGOOD at

tD1 + tD2, when the precharged output is above VBOOT but below

OVP, it walks down to VBOOT at RAMP_RATE and then releases

PGOOD at tD1 + tD2, in which tD2 is defined in Equation 4 and

longer than a normal start-up.

tD2 = V----R-P---A-R----EM----C-P---H--_--A-R---R--A--G--T---EE----D-- + V-----P----R----E----CR----H-A---A-M---R---P-G---_--E-R---D--A---â-T---EV-----B----O----O-----T- ï¨ïsï©

(EQ. 4)

ISL68201 supports precharged load start-up up to the maximum

VOUT of 5.5V with sufficient boot capacitor charge. For an

extended precharged load, the boot capacitor will be discharged

to âPVCC - VOUT - VDâ by high-side drive circuitsâ standby current.

For instance, an extended 4V precharged load, the boot capacitor

will reduce to a less-than-1V boot capacitor voltage, which is

insufficient to power up the VR; in this case, it is recommended

to let the output drop below 2.5V with an external bleed resistor

before issuing another soft-start command.

Boot-Up Voltage Programming

An 8-bit pin PROG1 is dedicated for the boot-up voltage

programmability, which offers 256 options 0V and 0.5V to 5.5V,

as in Table 7. The most popular boot-up voltage levels are placed

on the tie-low spots (0h, 20h, 40h, 60h, 80h, A0h, C0h, E0h) and

the tie-high spots (1Fh, 3Fh, 5Fh, 7Fh, 9Fh, BFh, DFh, FFh) for

easy programming, as summarized in Table 3. 0V boot-up

voltage is considered as âOFF,â the driver will be in tri-state and

the internal DAC will set to 0V.

In addition, if the VOUT_COMMAND (21h) is executed

successfully 5.5ms (typically, worst 6.5ms) after VCC POR and

prior to Enable, it will override the boot-up voltage set by the

PROG1 pin.

TABLE 7. PROG1 8-BIT (BOOT-UP VOLTAGE)

BINARY

CODE

HEX

CODE

VBOOT

(V)

VOUT

COMMAND

CODE (HEX)

DELTA FROM

CODE (mV)

00000000

0.7969

00000001

0.5000

00000010

0.5078

7.8125

00000011

0.5156

7.8125

00000100

0.5234

7.8125

00000101

0.5313

7.8125

00000110

0.5391

7.8125

00000111

0.5469

7.8125

00001000

0.5547

7.8125

00001001

0.5625

7.8125

00001010

0.5703

7.8125

00001011

0.5781

7.8125

00001100

0.5859

7.8125

00001101

0.5938

7.8125

00001110

0.6016

7.8125

00001111

0.6094

7.8125

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March 7, 2016

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