7

FN3180.6

October 2, 2015

High output currents can be obtained only as far as package

dissipation allows. It is strongly recommended that output

current-limit sensing be used in such cases.

Current-Limit Sensing - The on-chip comparator (C in the

Functional Diagram) permits shutdown of the regulator

output in the event of excessive current drain. As Figure 8

voltage feedback is by-passed and the regulator output will

be limited to this current. Therefore, when the maximum load

Logic-Controllable Shutdown - When equipment is not

needed continuously (e.g., in remote data-acquisition

systems), it is desirable to eliminate its drain on the system

until it is required. This usually means switches, with their

unreliable contacts. Instead, the ICL7663S can be shut

drain on the power source. Since this pin must not be left

open, it should be tied to ground if not needed. A voltage of

less than 0.3V for the ICL7663S will keep the regulator ON,

turn the outputs OFF. If there is a possibility that the control

from this signal should be limited to 100

A maximum by a

high value (1M

) series resistor. This situation may occur

when the logic signal originates from a system powered

separately from that of the regulator.

Additional Circuit Precautions - This regulator has poor

rejection of voltage fluctuations from AC sources above

10Hz or so. To prevent the output from responding (where

this might be a problem), a reservoir capacitor across the

load is advised. The value of this capacitor is chosen so that

the regulated output voltage reaches 90% of its final value in

20ms. From:

In addition, where such a capacitor is used, a current-limiting

resistor is also suggested (see “Current-Limit Sensing”).

Producing Output Voltages with Negative Temperature

Coefficients -The ICL7663S has an additional output which

is 0.9V relative to GND and has a tempco of +2.5mV/°C. By

applying this voltage to the inverting input of amplifier A (i.e.,

produced. The TC of the output voltage is controlled by the

Applications

Boosting Output Current with External Transistor

The maximum available output current from the ICL7663S is

40mA. To obtain output currents greater than 40mA, an

external NPN transistor is used connected as shown in

Figure 10.

SHDN

SENSE

GND

0.047

F

604k



20



210k



10

+5V

FIGURE 8. POSITIVE REGULATOR WITH CURRENT LIMIT

I =

V

C

,C

t

=

= 0.022

-

+

-

+

FIGURE 9. GENERATING NEGATIVE TEMPERATURE

COEFFICIENTS

(

1 +

)

+

EQ. 2:

-

SHDN

SENSE

GND

10

F

604k



100



210k



+5V

0.47



EXTERNAL PIN

POWER

TRANSISTOR

FIGURE 10. BOOSTING OUTPUT CURRENT WITH EXTERNAL

TRANSISTOR

ICL7663S