ICL7663S_15 Datasheet, PDF (7/8 Pages) Intersil Corporation – CMOS Programmable Micropower Positive Voltage Regulator

ICL7663S
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, R_CL, is placed in series
with V_OUT2 and the SENSE terminal is connected to the
load side of R_CL. When the current through R_CL is high
enough to produce a voltage drop equal to V_CL (0.5V) the
voltage feedback is by-passed and the regulator output will
be limited to this current. Therefore, when the maximum load
current (I_LOAD) is determined, simply divide V_CL by I_LOAD to
obtain the value for R_CL.
V+_IN SENSE
20
V_OUT2
V_OUT1
R_CL
0.047F
V_IN
V_TC ^{604k R2}
V_SET
10F
C_L
V_OUT
+5V
GND SHDN _{210k R1}
R₂ + R₁
V_OUT = _R1
V_SET = 5V
V_CL
I_CL = _RCL = 25mA
FIGURE 8. POSITIVE REGULATOR WITH CURRENT LIMIT
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 I_Q (under 4A) 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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:
V
I = C ,C
=
(20
x
10^-3)
=
0.022
I_OUT
t I_OUT 0.9V_OUT
V_OUT
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.,
the V_SET 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).
R₁
R₂
R₃
V_SET
+
- ^VTC
+
-^VREF
V_OUT
EQ. 1:
V_OUT = V_SET
(₁₊
R₂ )
R₁
+
R₂
R₃
(V_SET
-
V_TC)
EQ. 2:
TC V_OUT =
-
R₂
R₃
(TC V_TC) in mV/°C
Where:V_SET = 1.3V
V_TC = 0.9V
TCV_TC = +2.5mV/°C
FIGURE 9. GENERATING NEGATIVE TEMPERATURE
COEFFICIENTS
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.
V+_IN V_OUT1
V_OUT2
100
EXTERNAL PIN
POWER
TRANSISTOR
0.47
10F
V_IN
SENSE
604k
V_SET
V_OUT
+5V
GND SHDN
210k
FIGURE 10. BOOSTING OUTPUT CURRENT WITH EXTERNAL
TRANSISTOR
7
FN3180.6
October 2, 2015