ISL6436LIB 查看數據表（PDF） - Renesas Electronics

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ISL6436LIB

USB Dual Port Power Supply Controller

Renesas Electronics 

ISL6436

Key Feature Description and Operation

UV Lock Out

The ISL6436 undervoltage lockout feature prevents functionality

of the device unless the correct ENABLE state and VIN > 2.5V

are present.

Soft Start

A constant 500nA current source ramps up the switch’s gate

causing a voltage follower effect on the output voltage. This

provides a soft start turn-on eliminating bus voltage drooping

caused by in-rush current charging heavy load capacitances.

Rising and falling outputs are current limited voltage ramps so that

both the inrush current and voltage slew rate are limited,

independent of load. This reduces supply droop due to surge and

also eliminates the need for EMI filters necessary on other IC

products.

Fault Blanking On Start-Up

During initial turn-on the ISL6436 prevents nuisance faults being

reported to the system controller by blanking the fault signal for

12ms. This blanking eliminates the need for external RC filters

necessary for other vendor products that assert a fault signal

upon initial turn-on into a temporary high current condition. See

Figures 10 through 12 for waveform examples.

Current Regulation

The ISL6436 has integrated current sensing on the power

MOSFET that allows for rapid control of OC events. Once an OC

is detected the ISL6436 goes into its current regulation (CR)

control mode. The ISL6436 CR level is set to a nominal 1A. This

current regulation is 25% over the full operating temperature and

voltage bias range. See Figures 4 and 5 for illustrative curves.

The speed of this control is inversely related to the magnitude of

the OC fault. Thus a hard over current is more quickly controlled

than a marginal OC condition. See Figure 6 for waveforms

illustrating this and Figure 7 for an accompanying graph.

Over Temperature Shutdown

Although the ISL6436 has a thermal shutdown feature, because

of the 12ms timed shutdown this will only be invoked in extremely

high ambient temperatures.

Latch-Off Time Delay

The primary function of any OC protection device is to quickly

isolate the voltage bus from a faulty load. Unlike many other IC

products that sense the IC thermal condition (the monitored IC

junction temperature depends on a number of factors the most

important of which are power dissipation of the faulted and

adjacent switches and package temp) to isolate a faulty load,

the ISL6436 uses an internal 12ms timer that starts upon OC

detection. Once an OC condition is detected the appropriate

output is current limited for a maximum of 12ms to allow

transient conditions to pass before latch-off. This time to latch-off

is independent of device thermal or adjacent switch condition.

See Figure 18 for waveforms illustrating independent latch-off.

If, after the ISL6436 has latched off, and the fault has asserted

and, the enable is not deasserted but the OC condition still

exists, the ISL6436 unlike other IC devices does not send to the

controller a continuous string of fault pulses. The ISL6436’s

single fault signal is sent at the time of latch-off unlike other

devices.

Slow And Fast Shutdown

The ISL6436 has two shutdown modes. When turned off with

a load current less than the current regulation (CR) level the

ISL6436 shuts down in a controlled manner using a 500nA

constant current source controlled ramp. When latched off

due to CR and the timer has expired, the ISL6436 quickly

pulls down the output thereby quickly removing the faulted

load from the voltage bus. See Figures 8 and 9 for waveforms

of each mode.

Active Output Pulldown

Another unique ISL6436 feature is the active pull down on the

outputs to 300mV above GND when the device is disabled.

Competitors’ parts’ switch leakage causes the output voltage

to drift up to VIN voltage even when the part is supposed to

be disabled.

ON OFF

ENABLE

FAULT

VOUT

LATCH-OFF SET

RESET BY

ENABLE

CURRENT

REGULATION

SETTLING TIME

(1.4ms)

OVER CURRENT

IOUT

1A CURRENT

LIMIT

12ms CURRENT REGULATION PERIOD

FIGURE 1. TYPICAL OPERATIONAL WAVEFORMS

FN9023 Rev 0.00

Aug 10, 2001

Page 5 of 13

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