ISL6416 查看數據表（PDF） - Renesas Electronics

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ISL6416

Triple Output, Low-Noise LDO Regulator with Integrated Reset Circuit

Renesas Electronics 

ISL6416

Pin Descriptions

VOUT1 - This pin is the output for LDO1. Bypass with a

minimum of 2.2µF, low ESR ceramic capacitor to GND for

stable operation.

VIN - Supply input pins. Connect to input power source.

Bypass with a minimum 2.2µF capacitor to GND. Both VIN

pins must be tied together on the PC board, close to the IC.

GND - Ground for LDO1, LDO2, and LDO3.

CC1 - Compensation Capacitor for LDO1. Connect a

0.033µF capacitor from CC1 to GND.

SHDN - Shutdown input for all LDOs. This pin is pulled up

internally. Drive this pin LOW to turn off all LDOs.

VOUT2 - This pin is the output for LDO2. Bypass with a

minimum of 2.2µF, low ESR capacitor to GND for stable

operation.

CT - Timing pin for the RESET circuit pulse width. A

capacitor connected from this pin to GND will set a delay the

RESET delay. Leaving this pin open will make the RESET

delay approximately zero.

CC2 - Compensation capacitor for LDO2. Connect a

0.033µF capacitor from CC2 to GND.

VOUT3 - This pin is output for LDO3. Bypass with a

minimum of 2.2µF, low ESR capacitor to GND3 for stable

operation.

CC3 - Compensation capacitor for LDO3. Connect a

0.033µF capacitor from CC3 to GND3.

FAULT - This is the power good indicator for LDO1. When

the 1.8V output is out of regulation this pin goes LOW. This

pin also goes LOW during thermal shutdown or an

overcurrent event on LDO1. Leave floating if not used.

RESET - This pin is the active-LOW output of the push-pull

output stage of the integrated reset supervisory circuit. The

reset circuit monitors VIN and asserts a RESET output at this

pin, if VIN falls below the reset threshold. The RESET output

remains LOW, while the VIN pin voltage is below the reset

threshold, and for a time set by the CT capacitor, after VIN

rises above the reset threshold.

Functional Description

The ISL6416 is a 3-in-1 multi-output, low dropout, regulator

designed for wireless chipset power applications. It supplies

three fixed output voltages 1.8V, 2.8V and 2.8V. Each LDO

consists of a 1.2V reference, error amplifier, MOSFET driver,

P-Channel pass transistor, dual-mode comparator and

internal feedback voltage divider.

The 1.2V band gap reference is connected to the error

amplifier’s non-inverting input. The error amplifier compares

this reference to the selected feedback voltage and amplifies

the difference. The MOSFET driver reads the error signal

FN9193 Rev 0.00

Nov 3, 2004

and applies the appropriate drive to the P-Channel pass

transistor. If the feedback voltage is lower then the reference

voltage, the pass transistor gate is pulled lower, allowing

more current to pass and increasing the output voltage. If the

feedback voltage is higher than the reference voltage, the

pass transistor gate is driven higher, allowing less current to

pass to the output. The output voltage is fed back through an

internal resistor divider connected to OUT1/2/3 pins.

Additional blocks include an output overcurrent protection,

thermal sensor, fault detector, RESET function and

shutdown logic.

Internal P-Channel Pass Transistors

The ISL6416 features a typical 0.5 rDS(ON) P-channel

MOSFET pass transistor. This provides several advantages

over similar designs using PNP bipolar pass transistors. The

P-Channel MOSFET requires no base drive, which reduces

quiescent current considerably. PNP based regulators waste

considerable current in dropout when the pass transistor

saturates. They also use high base drive currents under

large loads. The ISL6416 does not suffer from these

problems.

Integrated Reset for MAC/ Baseband Processors

The ISL6416 includes a microprocessor supervisory block.

This block eliminates the extra reset IC and external

components needed in wireless chipset applications. This

block performs a single function; it asserts a RESET signal

whenever the VIN supply voltage decreases below a preset

threshold, keeping it asserted for a programmable time (set

by external capacitor CT) after the VIN pin voltage has risen

above the reset threshold. The reset threshold for the

ISL6416 is 2.63V typical.

The voltage at the CT pin is compared to the 1.2V bandgap

voltage. The charging of the CT capacitor behaves like an

RC network and the RESET delay can be approximated by:

Td = -R*C*ln(1-1.2V/VIN)

Where C is the capacitor at CT, and R is 11.1M for

VIN = 3.3V. With no capacitor on the CT pin the RESET

delay will be close to zero. Figure 12 shows the RESET

delay vs CT capacitance.

500

400

300

200

100

0

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0

CT (µF)

FIGURE 12. RESET DELAY vs CT CAPACITANCE

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