LT1175IST-5#PBF Linear Technology, LT1175IST-5#PBF Datasheet - Page 13

• Manufacturer Part Number: LT1175IST-5#PBF
• Description: IC LDO REG NEG 5V 500MA SOT223-3
• Manufacturer: Linear Technology

Specifications of LT1175IST-5#PBF

• Regulator Topology: Negative Fixed
• Voltage - Output: -5V
• Voltage - Input: Down to -20V
• 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: Surface Mount
• Package / Case: SOT-223 (3 leads + Tab), SC-73, TO-261
• Primary Input Voltage: 20V
• Output Voltage Fixed: 5V
• Dropout Voltage Vdo: 500mV
• No. Of Pins: 3
• Output Current: 500mA
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free by exemption / RoHS Compliant

APPLICATIONS INFORMATION
T
T
θ
V
I
Example: LT1175S8 with I
V
LT1175S8 is 125°C. Thermal resistance from Table 2 is
found to be 80°C/W.
Output Voltage Reversal
The LT1175 is designed to tolerate an output voltage
reversal of up to 2V. Reversal might occur, for instance,
if the output was shorted to a positive 5V supply. This
would almost surely destroy IC devices connected to the
negative output. Reversal could also occur during start-
up if the positive supply came up fi rst and loads were
connected between the positive and negative supplies.
For these reasons, it is always good design practice to
add a reverse biased diode from each regulator output to
ground to limit output voltage reversal. The diode should
be rated to handle full negative load current for start-up
situations, or the short-circuit current of the positive supply
if supply-to-supply shorts must be tolerated.
Input Voltage Lower Than Output
Linear Technology’s positive low dropout regulators
LT1121 and LT1129, will not draw large currents if the
input voltage is less than the output. These devices use a
lateral PNP power transistor structure that has 40V emitter
base breakdown voltage. The LT1175, however, uses an
NPN power transistor structure that has a parasitic diode
LOAD
A
MAX
JA
IN
IN
Die Temperature = 60 + 80 (0.2A)(8 – 5) = 108°C
Maximum
Maximum Continuous
Input Voltage
(for Thermal Considerations)
= 7V, T
= Maximum ambient temperature
= Maximum LT1175 die temperature (125°C for
= LT1175 thermal resistance, junction to ambient
= Maximum continuous input voltage at maximum
= Maximum load current
commercial and industrial grades)
load current
A
= 60°C. Maximum die temperature for the
Power Dissipation =
LOAD
= 200mA, V
=
125 – 60
125 – 60
80 0 2
80
( )
.
OUT
=
+ =
0 81
5 9
.
= 5V,
W
V
between the input and output of the regulator. Reverse
voltages between input and output above 1V will damage
the regulator if large currents are allowed to fl ow. Simply
disconnecting the input source with the output held up
will not cause damage even though the input-to-output
voltage will become slightly reversed.
High Frequency Ripple Rejection
The LT1175 will sometimes be powered from switching
regulators that generate the unregulated or quasi-regulated
input voltage. This voltage will contain high frequency ripple
that must be rejected by the linear regulator. Special care
was taken with the LT1175 to maximize high frequency
ripple rejection, but as with any micropower design,
rejection is strongly affected by ripple frequency. The
graph in the Typical Performance Characteristics section
shows 60dB rejection at 1kHz, but only 15dB rejection at
100kHz for the 5V part. Photographs in Figures 4a and 4b
show actual output ripple waveforms with square wave
and triwave input ripple.
100mV/DIV
100mV/DIV
100mV/DIV
20mV/DIV
OUTPUT
OUTPUT
RIPPLE
RIPPLE
INPUT
INPUT
Figure 4a.
5μs/DIV
2μs/DIV
Figure 4b.
1175 F04a
1175 F04b
LT1175
C
C
f = 50kHz
C
C
f = 100kHz
OUT
OUT
OUT
OUT
= 4.7μF TANT
= 1μF TANT
= 4.7μF TANT
= 1μF TANT
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