Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsLinear ICsLinear IC - Op-amp Voltage feedback SO 8

10 100

FREQUENCY (MHz)

100

1000

I INCREASE (mA)

10V supply (1 amplifier)

10V supply (2 amplifiers)

30V supply

(1 amplifier)

10V

15V

24V

20V

30V supply

(2 amplifiers)

8-Pin SO PowerPAD

= 47°C/W

T = 85°C

T = 140°C

LM7372

SNOS926E –MAY 1999–REVISED MARCH 2013

www.ti.com

Figure 27. Power Supply Current Increase

Figure 27 shows that there could be 1mA or more excess supply current per amplifier with close to full output

swing (24V

) when frequency is just above 1MHz (or at higher frequencies when the output swing is less). This

boost in supply current enables the output to “keep up” with high frequency/large signal output swing, but in turn,

increases the total package power dissipation and therefore raises the device junction temperature. As a

consequence, these demanding applications, especially ones which run at higher supply voltages, need special

attention to the package heatsink design. For that reason, Figure 27 has the safe operating limits for the 8-Pin

SO PowerPAD package (e.g. “30V supply (2 amplifiers)” horizontal line) superimposed on top of it (with T

limit of

140°C when operated at 85°C ambient), so that the designer can readily decide whether or not there is need for

additional heat sinking.

For example, if the LM7372 is operating similarly to Figure 1 schematic with a single power supply of 10V,

Figure 27 shows that it is safe to have up to 10V

output swing at up to 40MHz with no additional heat sinking.

This determination is from inspection of Figure 27 where the “10V supply (2 amplifiers)” safe operating limit

intercepts the 10V

swing graph at around 40MHz. Use the “10V supply (1 amplifier)” safe operating limit line in

cases where the second amplifier in the LM7372 package does not experience high frequency/high output swing

conditions.

At any given “I

increase” value (y axis), the product of frequency and output swing remains essentially constant

for all output swing plots. This holds true for the lower frequency range before the plots experience a slope

increase. Therefore, if the application example just discussed operates up to 60MHz instead, it is possible to

calculate the junction-temperature-limited maximum output swing of 6.7V

(= 40MHz x 10V

/60MHz) instead.

Please note that Figure 27 precludes any additional amplifier power dissipation related to load (this topic is

discussed below in detail). This load current, if large enough, will reduce the operating frequency/output swing

further. It is important to note that the LM7372 can be destroyed if it is allowed to dissipate enough power that

compromises its maximum junction temperature limit of 150°C.

With the op amp tied to a load, the device power dissipation consists of the quiescent power due to the supply

current flow into the device, in addition to power dissipation due to the load current. The load portion of the

power itself could include an average value (due to a DC load current) and an AC component. DC load current

would flow if there is an output voltage offset, or the output AC average current is non-zero, or if the op amp

operates in a single supply application where the output is maintained somewhere in the range of linear

operation. Therefore:

Product Folder Links: LM7372