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AD1315

High Speed Active Load with Inhibit Mode

HANAMICRON 

AD1315

FUNCTIONAL DESCRIPTION

The AD1315 is a complete high speed active load designed for

use in general purpose instrumentation and digital functional

test equipment. The function of the active load is to provide

independently variable source and sink currents for the device to

be tested.

The equivalent circuit for the AD1315 is shown in Figure 11.

An active load performs the function of loading the output of

the device under test with a programmed IOH or IOL. These

currents are independently programmable. VCOM is the commu-

tation voltage point at which the load switches from source to

sink mode. The active load may also be inhibited, steering cur-

rent to the IOLRTN and IOHRTN pins, effectively disconnecting it

from the test pin.

The AD1315 accepts differential digital signals at its inhibit

inputs ensuring precise timing control and high noise immunity.

The wide inhibit input voltage range allows for ECL power

supplies of –5.2 V and 0 V, –3.2 V and +2 V, and 0 V and +5 V.

Where speed and timing accuracy are less important, TTL or

CMOS logic levels may be used to toggle the Inhibit inputs of

the AD1315. Single ended operation is possible by biasing one

of the inputs to approximately +1.3 V for TTL or VCC/2 for

CMOS. Care should be taken to observe the 4 V maximum

allowable input voltage.

The IOH and IOL programming inputs accept 0 V to +5 V analog

inputs, corresponding to 0 to 50 mA output currents. The VCOM

input, which sets the IOH/IOL switch point, may be set anywhere

within the input range of –2 V to +7 V.

Figure 11. Block Diagram

Figure 12. Allowable Current Range for IOH, IOL vs. VDUT

Ideally, the commutation point set at VCOM would provide in-

stantaneous current sink/source switching. Because of I/V

characteristics of the internal bridge diodes, this is not the case.

To guarantee full current switching at the DUT, at least a 1 volt

difference between VCOM and VDUT must be maintained in

steady state conditions. Because of the relatively fast edge rates

exhibited by typical logic device outputs, this should not be a

problem in normal ATE applications.

INHIBIT MODE LEAKAGE

The AD1315’s inhibit-mode leakage current changes with both

temperature and bias levels. There are two major contributing

effects: transistor reverse-bias collector-base leakage and reverse

leakage in the Schottky-diode bridge. Leakage variations with

VDUT arise primarily from transistor collector-base leakage,

while both effects contribute to leakage current temperature

variations. Inhibit-mode leakage is weakly dependent on VCOM

and decreases slightly as the difference between VDUT and VCOM

is reduced. Figure 8 shows typical AD1315 inhibit leakage cur-

rent as a function of VDUT and temperature.

THERMAL CONSIDERATIONS

The AD1315 is provided in a 0.550" ϫ 0.550", 16-lead (bottom

brazed) gull wing, surface mount package with a θJC of 10°C/W

(typ). Thermal resistance (case-to-ambient) vs. air flow for the

AD1315 in this package is shown in Figure 13. The data pre-

sented is for a ZIF socketed device. For PCB mounted devices

(w/30 mils clearance) the thermal resistance should be ~3 to 7%

lower with air flows below 320 lfm(1). Notice that the improve-

ment in thermal resistance vs. air flow starts to flatten out just

above 400 lfm(2).

NOTES

1Ifm is air flow in linear feet/minute.

2For convection cooled systems, the minimum recommended airflow is 400 lfm.

VDUT VOLTAGE RANGE

In Figure 12, VDUT range, IOH and IOL typical current maxi-

mums are plotted versus DUT voltage. In the IOH mode (VDUT

higher than VCOM), the load will sink 50 mA, until its output

starts to saturate at approximately –1.5 V. In the IOL mode

(VDUT lower than VCOM), the load will source 50 mA until its

output starts to saturate at approximately +5.5 V. At +7 V, the

source current will be close to zero.

Figure 13. Case-to-Ambient Thermal Resistance vs.

Air Flow

–6–

REV. A

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