ICL7663SCBA datasheet(6/7 Pages) INTERSIL

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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

shows, a current-limiting resistor, RCL, is placed in series

with VOUT2 and the SENSE terminal is connected to the

load side of RCL. When the current through RCL is high

enough to produce a voltage drop equal to VCL (0.5V) the

voltage feedback is by-passed and the regulator output will

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

current (ILOAD) is determined, simply divide VCL by ILOAD to

obtain the value for RCL.

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

down by a logic signal, leaving only IQ (under 4µA) as a

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,

and a voltage level of more than 1.4V but less than V+IN will

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

signal could exceed the regulator input (V+IN) the current

from this signal should be limited to 100

µA maximum by a

high value (1M

Ω) 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/oC. By

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

the VSET pin), output voltages having negative TC may be

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

R2/R3 ratio (see Figure 9 and its design equations).

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

VOUT2

VOUT1

VTC

VSET

SENSE

GND

VIN

0.047

µF

V+IN

604k

Ω

RCL

Ω

210k

Ω

µF V

OUT

+5V

FIGURE 8. POSITIVE REGULATOR WITH CURRENT LIMIT

VOUT =

R2 + R1

VSET = 5V

ICL =

VCL

RCL

= 25mA

I =

∆V

∆t

IOUT

(20 x 10-3)

0.9VOUT

= 0.022

IOUT

VOUT

VREF

VSET

VTC

VOUT

Where:VSET = 1.3V

VTC = 0.9V

TCVTC = +2.5mV/

FIGURE 9. GENERATING NEGATIVE TEMPERATURE

COEFFICIENTS

EQ. 1: VOUT = VSET

(

1 +

)

(VSET - VTC)

EQ. 2:

TC VOUT =

(TC VTC) in mV/

SHDN

VOUT2

VOUT1

VSET

SENSE

GND

VIN

µF

V+IN

604k

Ω

100

Ω

210k

Ω

VOUT

+5V

0.47

Ω

EXTERNAL PIN

POWER

TRANSISTOR

FIGURE 10. BOOSTING OUTPUT CURRENT WITH EXTERNAL

TRANSISTOR

ICL7663S

ICL7663SCBA Datasheet(PDF) 6 Page - Intersil Corporation

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