cs5258-1 ON Semiconductor, cs5258-1 Datasheet - Page 7

• Manufacturer Part Number: cs5258-1
• Description: 8.0 A Ldo 5?pin Adjustable Linear Regulator
• Manufacturer: ON Semiconductor

Adjustable Operation
range of 1.25 V to 5.0 V. An external resistor divider sets the
output voltage as shown in Figure 16. The regulator’s
voltage sensing error amplifier maintains a fixed 1.253V
reference between the output pin and the adjust pin.
current to flow to ground. This current creates a voltage
across R2 that adds to the 1.253 V across R1 and sets the
overall output voltage. The adjust pin current (typically
50 μA) also flows through R2 and adds a small error that
should be taken into account if precise adjustment of V
is necessary. The output voltage is set according to the
formula:
adjust pin current.
10 mA. R1 and R2 should be of the same composition for
best tracking over temperature. The divider resistors should
be located as close to the load as possible.
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.
Other Adjustable Operation Considerations
specification of 6.0 V for the voltage difference between V
and V
in excess of 6.0 V. The two main considerations in such a
design are the sequencing of power supplies and short circuit
capability.
V
CONTROL
This LDO adjustable regulator has an output voltage
A resistor divider network R1 and R2 causes a fixed
The term I
R1 is chosen so that the minimum load current is a least
While not required, a bypass capacitor connected between
The CS5258−1 linear regulator has an absolute maximum
Power supply sequencing should be such that the
Figure 16. An External Resistor Divider Sets the
Value of V
OUT
V OUT + 1.253 V
. However, the IC may be used to regulate voltages
supply is brought up coincidentally with or
ADJ
OUT
DESIGN GUIDELINES
× R2 represents the error added by the
V
V
. The 1.253 V Reference Voltage
CONTROL
POWER
Drops Across R1.
CS5258−1
Adjust
R1 ) R2
R1
V
SENSE
V
) R2
OUT
I ADJ
R1
R2
http://onsemi.com
OUT
IN
7
before the V
charging the output capacitor as soon as the V
V
conducts. As V
remain in dropout, and current is passed to the load until
V
brings the pass transistor out of dropout. In this manner, any
output voltage less than 13 V may be regulated, provided the
V
where V
theoretical limit to the regulated voltage as long as the
V
− V
circuit conditions will result in the immediate operation of
the pass transistor outside of its safe operating area.
Overvoltage 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 the V
if fail safe operation is required. One possible clamp circuit
is illustrated in Figure 17; 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 condition
indefinitely while protecting the IC.
Stability Considerations
main characteristics of a linear regulator: start−up delay,
load transient response, and loop stability.
size and temperature constraints. A tantalum or aluminum
electrolytic capacitor is best, since a film or ceramic
capacitor with almost zero ESR can cause instability. The
aluminum electrolytic capacitor is the least expensive
OUT
OUT
POWER
POWER
There is a possibility of damaging the IC when V
The output compensation capacitor helps determine three
The capacitor value and type is based on cost, availability,
IN
External Supply
is in regulation. Further increase in the supply voltage
is greater than 6.0 V if a short circuit occurs. Short
differential is large enough that the pass transistor
Figure 17. Example Clamp Circuitry for
CONTROL
to V
to V
POWER
V
V
POWER
CONTROL
POWER
OUT
OUT
POWER
V
differential is less than 6.0 V. In the case
differential of 6.0 V is not exceeded.
POWER
and V
V
to V
ADJ
supply. This allows the IC to begin
increases, the pass transistor will
V
OUT
SENSE
POWER
− V
V
OUT
differential to less than 6.0 V
OUT
> 6.0 V
are shorted, there is no
POWER
POWER
to