TCL1584 Datasheet, PDF (6/13 Pages) TelCom Semiconductor, Inc – 7A / 5A / 4.6A / 3A, FAST RESPONSE, LOW DROPOUT POSITIVE LINEAR VOLTAGE REGULATORS

PRELIMINARY INFORMATION
TCL1584
TCL1585
TCL1587
7A / 5A / 4.6A / 3A, FAST RESPONSE,
LOW DROPOUT POSITIVE LINEAR
VOLTAGE REGULATORS
parameters will allow it. Typically, increasing the output
capacitance helps reduce the oscillation. NOTE: The
TCL1585 and TCL1584 have fixed current limit over the
entire voltage range and are not susceptible to this phenom-
enon.
Protection Diodes
The TCL158x family of devices do not normally require
any external current limiting circuitry such as protection
diodes, frequently used with older LDO regulators. A diode
is internally present between the output and input which is
capable of handling short-duration surge currents of up to
100A. This capability typically ensures safe operation ex-
cept for the case where output capacitance is exceedingly
large (>1000µF) and the input is suddenly shorted to ground.
This situation can produce excessive reverse current in the
device - enough to cause damage. An external high current
diode should be used as shown in Figure 2.
The ADJ pin does not normally need protection diodes
either. It can handle ±7V without any performance degrada-
tion or device damage. Current at this pin is internally limited
by a series resistor so the bypass capacitors do not present
any danger. Of course, exceeding 7V differential between
any two pins will cause catastrophic junction breakdowns
and possible damage to the device.
D1
1N4002
(OPTIONAL)
VIN
IN _{TCL1584-3.3 OUT}
+ _C1
10µF
GND
+ _C2
22µF
VOUT
Overload Recovery
The built-in Short Circuit and Safe-Operating-Area (SOA)
protection function of the TCL158x family can cause sec-
ondary effects which must be considered for robust system
design. The behavior of the regulator under heavy loads
(short circuit) at start-up is such that the output voltage will
remain low while sourcing maximum current until the load is
removed or reduced. Normally, the output voltage will rise as
the load is reduced and trace a line I-V relationship accord-
ing to the SOA limit. If the load line intersects this output
curve at two points the output voltage may not recover from
the heavy load/short-circuit condition. This condition is illus-
trated in Figure 3. The current limit constraint does not allow
any load point above it and the load line is defined absolutely
by the I-V characteristics of the load (a resistor, in this case).
Under these conditions it may be necessary to cycle the
power supply off and then on again. This phenomenon is
common for LDO’s with fold-back current limiting schemes.
NOTE: Overload recovery is always guaranteed on the
TCL1585 and TCL1587 because of the constant current
limit characteristic.
Ripple Rejection
A typical ripple rejection curve for the fixed output
voltage devices is shown in Figure 3. It is possible to obtain
improved performance in ripple rejection by using the ad-
justable output TCL158x with a bypass capacitor (C_ADJ)
shown in Figure 2. This capacitor should be chosen to have
a value such that its impedance at the ripple frequency is
less than R1 (see Figure 2.). Usually this is on the order of
100Ω. Example: If R1 = 100Ω and f_RIPPLE = 120Hz, the
bypass capacitor should be chosen to be 22µF or greater. If
these conditions are met the ripple rejection will be improved
by a factor of V_OUT/1.25 when compared to the performance
of the fixed output devices.
D1
1N4002
(OPTIONAL)
Current Limit Curve
VIN
C1 +
10µF
IN _{TCL1584 OUT}
ADJ
+ _CADJ
VOUT
R1 ⁺ C2
22µF
R2
Figure 2. Protection Diodes and C_ADJ
TCL1584/1585/1587-04 6/6/97
I_OUT
Load Line
Unrecoverable
I-V Point
Start Up
Point
V_IN – V_OUT (Constant V_IN)
Figure 3. Overload Recovery
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