cs5208-1 ON Semiconductor, cs5208-1 Datasheet - Page 5

• Manufacturer Part Number: cs5208-1
• Description: 8.0 A Ldo 3?pin Adjustable Linear Regulator
• Manufacturer: ON Semiconductor

PNP−NPN output stage that requires an output capacitor for
stability. A detailed procedure for selecting this capacitor is
included in the Stability Considerations section.
Design Guidelines
range of 1.25 V to 4.5 V. An external resistor divider sets the
output voltage as shown in Figure 11. The regulator’s
voltage sensing error amplifier maintains a fixed 1.25 V
reference between the output pin and the adjust pin.
to flow to ground. This current creates a voltage across R
adds to the 1.25 V across R
voltage. The adjust pin current (typically 50 μA) also flows
through R
account if precise adjustment of V
output voltage is set according to the formula:
pin current.
10 mA. R
tracking over temperature. The divider resistors should be
placed as close to the IC as possible and connected to the
output with a seperate metal trace.
the adjust pin and ground will improve transient response
and ripple rejection. A 0.1 μF tantalum capacitor is
recommended for “first cut” design. Value and type may be
varied to optimize performance vs price.
The CS5208−1 linear regulator has a composite
This LDO adjustable regulator has an output voltage
A resistor divider network R
The term I
R
While not required, a bypass capacitor connected between
1
is chosen so that the minimum load current is at least
V OUT + V REF
1
2
and R
and adds a small error that should be taken into
Adj
ADJUSTABLE OPERATION
THEORY OF OPERATION
× R
2
should be of the same composition for best
2
represents the error added by the adjust
V
Figure 11.
IN
CS5208−1
R 1 ) R 2
Adj
1
1
R 1
and R
V
and sets the overall output
OUT
OUT
2
causes a fixed current
) R 2
is necessary. The
R
R
1
2
I Adj
APPLICATION NOTES
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2
that
5
specification of 6.0 V for the voltage difference between V
and V
in excess of 6.0 V. The main considerations in such a design
are power−up and short circuit capability.
is fairly slow, typically on the order of several tens of
milliseconds, while the regulator responds in less than one
microsecond. In this case, the linear regulator begins
charging the output capacitor as soon as the V
differential is large enough that the pass transistor conducts
current. V
order of several hundred millivolts, so the pass transistor is
in dropout. As V
in dropout, and current is passed to the load until V
regulation. Further increase in V
out of dropout. The result is that the output voltage follows
the power supply ramp−up, staying in dropout until the
regulation point is reached. In this manner, any output
voltage may be regulated. There is no theoretical limit to the
regulated voltage as long as the V
6.0 V is not exceeded.
in a short circuit condition. Short circuit conditions will result
in the immediate operation of the pass transistor outside of its
safe operating area. Over−voltage stresses will then cause
destruction of the pass transistor before overcurrent or
thermal shutdown circuitry can become active. Additional
circuitry may be required to clamp V
to less than 6.0 V if failsafe operation is required. One
possible clamp circuit is illustrated in Figure 12; however, the
design of clamp circuitry must be done on an application by
application basis. Care must be taken to ensure the clamp
actually protects the design. Components used in the clamp
design must be able to withstand the short circuit conditions
indefinitely while protecting the IC.
OTHER ADJUSTABLE OPERATION CONSIDERATIONS
The CS5208−1 linear regulator has an absolute maximum
In most applications, ramp−up of the power supply to V
However, the maximum ratings of the IC will be exceeded
OUT
EXTERNAL SUPPLY
. However, the IC may be used to regulate voltages
OUT
V
is essentially at ground, and V
IN
IN
increases, the pass transistor will remain
V
Adj
V
OUT
Figure 12.
IN
IN
brings the pass transistor
to V
IN
to V
OUT
OUT
differential of
IN
IN
differential
is on the
to V
OUT
OUT
is in
IN
IN