OPA569 datasheet(13/28 Pages) TI1

13 / 28 page

OPA569

SBOS264A

www.ti.com

Current Limit Accuracy

Internally separate circuits monitor the positive and negative

current limits. Each circuit output is compared to a single

internal reference that is set by the user with an external

resistor or a resistor/voltage source combination. The OPA569

employs a patented circuit technique to achieve an accurate

and stable current limit throughout the full output range. The

initial accuracy of the current limit is typically within 3%;

however, due to internal matching limitations, the error can

be as much as 15%. The variation of the current limit with

factors such as output current level, output voltage and

temperature is shown in the Typical Characteristics section.

When the accuracy of one current limit (sourcing or sinking)

is more important than the other, it is possible to set its

accuracy to better than 1% by adjusting the external resistor

or the applied voltage. The accuracy of the other current limit

will still be affected by internal matching.

Current Limit Flag Pin

The OPA569 features a Current Limit Flag pin (pin 4) that

can be monitored to determine when the part is in current

limit. The output signal of the current limit flag pin is compat-

ible to standard logic in single supply applications. The

output signal is a CMOS logic gate that switches from V+ to

V– to indicate that the amplifier is in current limit. This flag

output pin can source and sink up to 25

µA. Additional

parasitic capacitance between pins 3 and 4 can cause

instability at the edge of the current limit. Avoid routing these

traces in parallel close to each other.

Quiescent Current Dependence on the

Current Limit Setting

The OPA569 is a low power amplifier, with a typical 3.4mA

quiescent current (with the current limit configured for 200mA).

The quiescent current varies with the current limit setting—

it increases 0.5mA for each additional 200mA increase in

the current limit, as shown in Figure 3.

FIGURE 3. Quiescent Current vs Current Limit Setting.

QUIESCENT CURRENT vs CURRENT LIMIT SETTING

Current Limit Setting (A)

0.5

1.5

2.5

FIGURE 4. Transimpedance Amplifier to Monitor Load

Current.

OPA569

O/475

MONITOR

O = –1V

at I

O = 1A

–2.5V

14,

12,

R = 475

Ω

–In

+In

+2.5V

OPA348

17,

CURRENT MONITOR

The OPA569 features an accurate output current monitor

(IMONITOR) without requiring the use of series resistance with

the load. This increases efficiency significantly and provides

better overall swing-to-supply performance.

An internal circuit creates a 1:475 copy of the output current.

This copy of the output current can be monitored indepen-

dently or it can be used in applications such as current

control drive, setting non-symmetric positive and negative

current limits or paralleling two or more devices for increased

output current drive. When not being used, the Current

Monitor pin may be left floating.

Some restrictions apply when using the current monitor

function. When the main amplifier is sourcing current, the

current monitor circuit must be sourcing current. Likewise,

when the main amplifier is sinking current, the current moni-

tor circuit must also be sinking current. Additionally, the

swing on the IMONITOR pin is smaller than the output swing.

When the amplifier is sourcing current, the voltage of the

Current Monitor pin must be at least two hundred millivolts

less than the output voltage of the amplifier. Conversely,

when the amplifier is sinking current, the voltage of the

Current Monitor pin must be at least two hundred millivolts

greater than the output voltage of the amplifier. Resistive

loads are able to meet these restrictions. Other types of

loads may cause invalid current monitor values.

A simple way to monitor the load current and meet these

requirements is to connect a resistor (with resistance less

than 400 • RL) from the IMONITOR pin to the same potential to

which the other side of the load is connected. Another

method is to use a transimpedance amplifier, as shown in

Figure 4. This circuit must assure that the potential of the

IMONITOR pin remains in the valid voltage range by connecting

it to the same potential to which the load is connected—most

likely ground for dual supply or mid-supply for single-supply

applications.

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