ISL8022 Просмотр технического описания (PDF) - Renesas Electronics

Номер в каталоге

Компоненты Описание

Список матч

ISL8022

Dual 2A/1.7A Low Quiescent Current 2.25MHz High Efficiency Synchronous Buck Regulator

Renesas Electronics 

ISL8022

PWM

PFM

CLOCK

IL

0

VOUT

16 CYCLES

PFM CURRENT LIMIT

NOMINAL +1.5%

NOMINAL

FIGURE 45. SKIP MODE OPERATION WAVEFORMS

LOAD CURRENT

Positive and Negative Overcurrent Protection

CSA1 and CSA2 are used to monitor output 1 and output 2

channels respectively. The overcurrent protection is realized by

monitoring the CSA_ output with the OCP threshold logic, as

shown in the “Block Diagram” on page 3. The current sensing

circuit has a gain of 0.32V/A, from the P-MOSFET current to the

CSA_ output. When the CSA_ output reaches the threshold of

1.25V for Channel 1 and 1.1V for Channel 2, the OCP comparator

is tripped to turn off the P-MOSFET immediately. The overcurrent

function protects the switching converter from a shorted output by

monitoring the current flowing through the upper MOSFETs.

Upon detection of an overcurrent condition, the upper MOSFET

will be immediately turned off and will not be turned on again

until the next switching cycle. Upon detection of the initial

overcurrent condition, the Overcurrent Fault Counter is set to 1

and the Overcurrent Condition Flag is set from LOW to HIGH. If,

on the subsequent cycle, another overcurrent condition is

detected, the OC Fault Counter will be incremented. If there are

seventeen sequential OC fault detections, the regulator will be

shut down under an Overcurrent Fault Condition. An Overcurrent

Fault Condition will result with the regulator attempting to restart

in a hiccup mode with the delay between restarts being 4 soft-

start periods. At the end of the fourth soft-start wait period, the

fault counters are reset and soft-start is attempted again. If the

overcurrent condition goes away prior to the OC Fault Counter

reaching a count of four, the Overcurrent Condition Flag will set

back to LOW.

In the event that the inductor current reaches -1.6A, the part

enters Negative Overcurrent Protection. At this point, all

switching stops and the part enters tri-state mode while the pull-

down FET is discharging the output until it reaches normal

regulation voltage, then the IC restarts switching.

PG

The power-good signal (PG), monitors both of the output

channels. When powering up, the open-collector Power-On-Reset

output holds low for about 1ms after VO1 and VO2 reaches the

preset voltages. The PG output also serves as a 1ms delayed

power-good signal. If one of the outputs is disabled, then PG only

monitors the active channels. There is an internal 1M pull-up

resistor.

UVLO

When the input voltage is below the undervoltage lock-out (UVLO)

threshold, the regulator is disabled.

Enable

The enable (EN1, EN2) input allows the user to control the turning

on or off the regulator for purposes such as power-up

sequencing. The regulator is enabled, there is typically a 600µs

delay for waking up the bandgap reference and the soft start-up

begins.

Soft Start-Up

The soft start-up eliminates the in-rush current during the

start-up. The soft-start block outputs a ramp reference to both

the voltage loop and the current loop. The two ramps limit the

inductor current rising speed as well as the output voltage speed

so that the output voltage rises in a controlled fashion. At the

very beginning of the start-up, the feedback voltage is less than

0.2V; hence the PWM operating frequency is 1/3 of the normal

frequency. In forced PWM mode, the IC will continue to start-up in

PFM mode to support pre-biased load applications.

Discharge Mode (Soft-Stop)

When a transition to shutdown mode occurs, or the output

undervoltage fault latch is set, the outputs discharge to GND

through an internal 100 switch.

Power MOSFETs

The power MOSFETs are optimized for best efficiency. The ON-

resistance for the P-MOSFET is typically 100m and the ON-

resistance for the N-MOSFET is typical 90m.

100% Duty Cycle

The ISL8022 features 100% duty cycle operation to maximize

the battery life. When the battery voltage drops to a level that the

ISL8022 can no longer maintain the regulation at the output, the

regulator completely turns on the P-MOSFET. The maximum

dropout voltage under the 100% duty-cycle operation is the

product of the load current and the ON-resistance of the P-

MOSFET.

FN7650 Rev 3.00

March 14, 2013

Page 15 of 18

Share Link: