LT1175IN8 Linear Technology, LT1175IN8 Datasheet - Page 11

• Manufacturer Part Number: LT1175IN8
• Description: IC LDO REG ADJST NEG 500MA 8-DIP
• Manufacturer: Linear Technology

Specifications of LT1175IN8

• Regulator Topology: Negative Adjustable
• Voltage - Output: -3.8 ~ -19.9 V
• Voltage - Input: -4.3 ~ -20 V
• Voltage - Dropout (typical): 0.5V @ 500mA
• Number Of Regulators: 1
• Current - Output: 500mA
• Current - Limit (min): Adjustable
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

This condition can occur with ceramic or fi lm capacitors
which often have an ESR under 0.1Ω. With previous de-
signs, the user was forced to add a real resistor in series
with the capacitor to guarantee loop stability. The LT1175
uses a unique AC feedforward technique to eliminate
this problem. C
often used in regulators to cancel the pole formed by the
output capacitor. It would normally be connected from the
regulated output node to the feedback node at the R1/R2
junction or to an internal node on the amplifi er as shown.
In this case, however, the capacitor is connected to the
internal structure of the power transistor. R
able parasitic collector resistance of the power transistor.
Access to the node at the bottom of R
in monolithic structures where Kelvin connections can
be made to the NPN buried collector layer. The loop now
responds as if R
and good loop stability is achieved even with extremely
low ESR in the output capacitor.
APPLICATIONS INFORMATION
F
C
is a conventional feedforward capacitor
were in series with the output capacitor
FEEDFORWARD
LT1175
NEGATIVE DC
FEEDBACK
AT LIGHT
LOADS
PATH
AC
Q3
R
N
A1
C
–
+
is available only
C
C
20pF
is the unavoid-
F
+
3.8V
Q2
Figure 3
V
IN
Q1
R
R1
R2
R
0.5Ω
LIM
C
The end result of all this attention to loop stability is that
the output capacitor used with the LT1175 can range in
value from 0.1μF to hundreds of microfarads, with an ESR
from 0Ω to 10Ω. This range allows the use of ceramic,
solid tantalum, aluminum and fi lm capacitors over a wide
range of values.
The optimum output capacitor type for the LT1175 is
still solid tantalum, but there is considerable leeway in
selecting the exact unit. If large load current transients
are expected, larger capacitors with lower ESR may be
needed to control worst-case output variation during
transients. If transients are not an issue, the capacitor
can be chosen for small physical size, low price, etc.
Concerns about surge currents in tantalum capacitors are
not an issue for the output capacitor because the LT1175
limits inrush current to well below the level which can
cause capacitor damage. Surges caused by shorting the
regulator output are also not a problem because tantalum
OUTPUT
SENSE
GND
PARASITIC
COLLECTOR
RESISTANCE
POWER
TRANSISTOR
CURRENT LIMIT
SENSE RESISTOR
ESR
C
OUT
LOAD
1175 F03
OUTPUT
LT1175
11
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