ISL62391IRTZ datasheet(13/20 Pages) INTERSIL

13 / 20 page

FN6666.5

April 7, 2011

The PGOOD pin indicates when the converter is capable of

supplying regulated voltage. It is an undefined impedance if

VIN is not above the rising POR threshold or below the POR

falling threshold. When a fault is detected, the ISL62391,

ISL62392, ISL62391C and ISL62392C will turn on the open-

drain NMOS, which will pull PGOOD low with a nominal

impedance of 32

Ω. This will flag the system that one of the

output voltages is out of regulation.

Separate enable pins allow for full soft-start sequencing.

Because low shutdown quiescent current is necessary to

prolong battery life in notebook applications, the PVCC 5V

LDO is held off until any of the three enable signals (EN1,

EN2 or LDO3EN) are pulled high. Soft-start of all outputs will

only start until after PVCC is above the 4.2V POR threshold.

In addition to user-programmable sequencing, the ISL62391,

ISL62392, ISL62391C and ISL62392C include a pre-

programmed sequential SMPS soft-start feature. Table 1

shows the SMPS enable truth table.

VCC

The VCC nominal operation voltage is 5V. If EN1, EN2 and

LDO3EN are all logic low, the VCC start-up voltage is 3.6V

when VIN is applied on ISL62391, ISL62392, ISL62391C

and ISL62392C. PVCC is held off until any of the three

enable signals (EN1, EN2 or LDO3EN) is pulled high. When

PVCC is above the 4.2V VCC POR threshold, VCC will

switchover to PVCC internally.

After VIN is applied, the VCC start-up 3.6V voltage can be used

as the logic high signal of any of EN1, EN2 and LDO3EN to

enable PVCC if there is no other power supply on the board.

MOSFET Gate-Drive Outputs LGATE and UGATE

The ISL62391, ISL62392, ISL62391C and ISL62392C have

internal gate-drivers for the high-side and low-side N-

Channel MOSFETs. The low-side gate-drivers are optimized

for low duty-cycle applications where the low-side MOSFET

conduction losses are dominant, requiring a low r DS(ON)

MOSFET. The LGATE pull-down resistance is small in order

to clamp the gate of the MOSFET below the VGS(th) at turn-

off. The current transient through the gate at turn-off can be

considerable because the gate charge of a low r DS(ON)

MOSFET can be large. Adaptive shoot-through protection

prevents a gate-driver output from turning on until the opposite

gate-driver output has fallen below approximately 1V. The

dead-time shown in Figure 25 is extended by the additional

period that the falling gate voltage stays above the 1V

threshold. The typical dead-time is 21ns. The high-side gate-

driver output voltage is measured across the UGATE and

PHASE pins while the low-side gate-driver output voltage is

measured across the LGATE and PGND pins. The power for

the LGATE gate-driver is sourced directly from the PVCC pin.

The power for the UGATE gate-driver is sourced from a “boot”

capacitor connected across the BOOT and PHASE pins. The

boot capacitor is charged from the 5V PVCC supply through a

“boot diode” each time the low-side MOSFET turns on, pulling

the PHASE pin low. The ISL62391, ISL62392, ISL62391C and

ISL62392C have integrated boot diodes connected from the

PVCC pins to BOOT pins.

Diode Emulation

FCCM is a logic input that controls the power state of the

ISL62391, ISL62392, ISL62391C and ISL62392C. If forced

high, the ISL62391, ISL62392, ISL62391C and ISL62392C

will operate in forced continuous-conduction-mode (CCM)

TABLE 1. SMPS ENABLE SEQUENCE LOGIC

EN1

EN2

START-UP SEQUENCE

All SMPS outputs OFF

FLOAT

All SMPS outputs OFF

SMPS1 OFF, SMPS2 ON

FLOAT

All SMPS outputs OFF

FLOAT

All SMPS outputs OFF

FLOAT

SMPS1 enables after SMPS2 is in regulation

SMPS1 ON, SMPS2 OFF

FLOAT

SMPS2 enables after SMPS1 is in regulation

All SMPS outputs ON simultaneously

FIGURE 24. SOFT-START SEQUENCE FOR ONE SMPS

VCC AND PVCC

PGOOD

1.5ms

2.75ms

tSOFTSTART

PGOOD DELAY

FIGURE 25. LGATE AND UGATE DEAD-TIME

50%

tLGFUGR

tUGFLGR

UGATE

LGATE

ISL62391, ISL62392, ISL62391C, ISL62392C

ISL62391IRTZ Datasheet(PDF) 13 Page - Intersil Corporation

ISL62391IRTZ Datasheet(HTML) 13 Page - Intersil Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL