ISL24021

9

FN6637.1

October 18, 2011

Applications Information

Product Description

The ISL24021 is a high output current, high voltage, rail-to-rail

voltage feedback amplifier. The ISL24021 is capable of ±1A

peak output short circuit current. The amplifier exhibits beyond

the rail input capability, rail-to-rail output capability and is unity

gain stable. Other features include fast slew rate and settling

time which is important in many applications, such as TFT-LCD

panels.

The ISL24021 is available in a 8 Ld 3mmx3mm TDFN package

featuring a standard operational amplifier pinout and a lead pitch

of 0.65mm. The device utilizes a thermally enhanced package and

has a built-in thermal protection circuit. It is specified for operation

over an ambient temperature range of -40°C to +85°C.

Operating Voltage, Input and Output

Capability

The ISL24021 can operate on a single supply or dual supply

configuration. The ISL24021 operating voltage ranges from a

minimum of 4.5V to a maximum of 19V. This range allows for a

standard 5V (or ±2.5V) supply voltage to dip to -10%, or a

standard 18V (or ±9V) to rise by +5.5% without affecting

performance or reliability.

The input common mode voltage range extends 0.5V beyond the

supply rails. For this range, the ISL24021 amplifier is immune to

phase reversal. If the common mode input voltage exceeds the

supply voltage by more than 0.5V, electrostatic protection diodes

in the input stage of the device begin to conduct. It is suggested

to not overdrive the inputs. Figure 23 shows the input voltage

driven beyond the supply rails and the device output swinging

between the supply rails.

The output swings of the ISL24021 typically extend to within

25mV of positive and negative supply rails with load currents of

±5mA. Decreasing load currents will extend the output voltage

range even closer to the supply rails. Figure 24 shows the input

and output waveforms for the device in a unity-gain

configuration. Operation is from ±5V supply with a 1k

Ω load

Refer to the “Electrical Specifications” tables beginning on

page 2 for specific device parameters. Parameter variations with

operating voltage, loading and/or temperature are shown in the

“Typical Performance Curves” on page 5.

.

Output Current Limit

The ISL24021 is capable of ±1A peak output short circuit

current. The device will limit the current to ±1A. Maximum

reliability is maintained if the output continuous current never

exceeds ±300mA. This limit is set by the characteristics of the

internal metal interconnects. See “Power Dissipation” on

page 10 for detailed information about ensuring device

operation with temperature and load conditions.

Driving Capacitive Loads

As load capacitance increases, the -3dB bandwidth will decrease

and peaking can occur. Depending on the application, it may be

necessary to reduce peaking and to improve device stability. To

improve device stability a snubber circuit or a series resistor may

be added to the output of the ISL24021.

A snubber is a shunt load consisting of a resistor in series with a

capacitor, see Figure 25. An optimized snubber can improve the

phase margin and the stability of the ISL24021. The advantage

of a snubber circuit is that it does not draw any DC load current or

reduce the gain.

Another method to reduce peaking is to add a series output

resistor (typically between 1

Ω to 10Ω; see Figure 26). Depending

on the capacitive loading, a small value resistor may be the most

appropriate choice to minimize any reduction in gain.

1V

1V

10µs

FIGURE 23. OPERATION WITH BEYOND-THE-RAILS INPUT

5V

5V

10µs

FIGURE 24. OPERATION WITH RAIL-TO-RAIL INPUT AND OUTPUT