ISL6567 datasheet(13/26 Pages) RENESAS

13 / 26 page

ISL6567

FN9243 Rev 4.00

Page 13 of 26

August 9, 2011

The differential amplifier can be used even if remote output

sensing is not desired or not feasible, simply connect RGND to

the local ground and connect VSEN to the output voltage being

monitored. Should one desire to bypass the differential

amplifier, the circuit in Figure 9 is recommended as the proper

implementation. Since its output is monitored for OVP and

PGOOD purposes, the differential amplifier needs to be

connected to the feedback circuit at all times, hence its input

connections to FB and local ground. However, its output, VDIFF,

can be left open. The resistor divider setting the output voltage

is calculated in a manner identical to that already revealed.

DIFFERENTIAL AMPLIFIER’S UNITY GAIN NETWORK

The differential amplifier on the ISL6567 utilizes a typical

resistive network along with active compensating circuitry to

set its unity gain. This resistive network can affect the DC

regulation setpoint in proportion to its relative magnitude

compared to the external output voltage setting resistor

divider. Figure 10 details the internal resistive network. For

minimal impact on the output voltage setting, follow the

guidelines presented in “Setting the Output Voltage” on

page 12.

EXTERNAL REFERENCE OPERATION

The ISL6567 is capable of accepting an external voltage and

using it as a reference for its output regulation. To enable this

mode of operation, the MON pin potential has to be below 3.5V

and the reference voltage has to be connected to the REFTRK

pin. The internal or external reference mode of operation is

latched in every time the POR is released or the ISL6567 is

enabled. The highest magnitude external reference fed to the

REFTRK pin that the ISL6567 can follow is limited to 2.3V. The

ISL6567 utilizes a small initial negative offset (typically about

50mV) in the voltage loop at the beginning of it soft-start, to

counteract any positive offsets that may have undesirable

effects. As this initial offset is phased out as the reference is

ramped up to around 200mV, in order to avoid an error in the

output regulation level, it is recommended the external

reference has an amplitude (final, DC level) exceeding 300mV.

While in external reference (ER) mode, the threshold sensitive

MON pin can be used to control when the ISL6567 starts to

monitor the output for PGOOD and OVP protection purposes.

As shown in Figure 11, connect the MON pin to the voltage to

be monitored via a resistor divider. An internal current source

helps set a user-adjustable monitor threshold hysteresis.

Choose resistor values according to desired hysteresis voltage,

VH, and desired rising threshold, VT. Make note that, in these

equations, VREF refers to the reference of the MON comparator

(300mV).

Intersil recommends the MON threshold is set to be tripped

when the external reference voltage reaches at least 90% of

the final DC value. Since PGOOD and OVP monitoring are

relative to the external reference magnitude, it is important to

understand that the PGOOD and OVP thresholds will move in

proportion to the moving reference (externally soft-started

reference). Thus, the absolute thresholds of PGOOD and OVP.

FIGURE 9. SETTING THE OUTPUT VOLTAGE AT THE FB PIN

EXTERNAL CIRCUIT

ISL6567

VSEN

RGND

DIFFERENTIAL

AMPLIFIER

To VOUT

VREF

ERROR

AMPLIFIER

RS(R1)

VDIFF

FIGURE 10. SETTING THE OUTPUT VOLTAGE AT THE INPUT OF

THE DIFFERENTIAL AMPLIFIER

EXTERNAL

ISL6567

VSEN

RGND

VDIFF

DIFFERENTIAL

AMPLIFIER

ZIN

CIRCUIT

~2µA

ZIN > 240k

OVER PROCESS, TEMPERATURE, AND

0 < VSEN-RGND < 2.5V

FIGURE 11. SETTING THE MONITORING THRESHOLD AND

HYSTERESIS

EXTERNAL CIRCUIT

ISL6567

MON

COMPARATOR

(300mV)

(10µA)

VCC

VREF

VDIFF

------

RS VREF



VT VREF

–

-------------------------

(EQ. 9)

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