LT3008 LINER [Linear Technology], LT3008 Datasheet - Page 10

• Manufacturer Part Number: LT3008
• Description: 3?A IQ, 20mA, 45V Low Dropout Linear Regulator
• Manufacturer: LINER [Linear Technology]

LT3008
APPLICATIONS INFORMATION
Voltage and temperature coeffi cients are not the only
sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress,
similar to the way a piezoelectric accelerometer or micro-
phone works. For a ceramic capacitor, the stress can be
induced by vibrations in the system or thermal transients.
The resulting voltages produced can cause appreciable
amounts of noise, especially when a ceramic capacitor is
used for noise bypassing. A ceramic capacitor produced
Figure 4’s trace in response to light tapping from a pencil.
Similar vibration induced behavior can masquerade as
increased output voltage noise.
10
500μV/DIV
V
OUT
Figure 4. Noise Resulting from Tapping
on a Ceramic Capacitor
V
C
I
LOAD
OUT
OUT
= 0.6V
= 22μF
= 10μA
100ms/DIV
3008 F04
Thermal Considerations
The LT3008’s maximum rated junction temperature of
125°C limits its power-handling capability. Two components
comprise the power dissipated by the device:
1. Output current multiplied by the input/output voltage
2. GND pin current multiplied by the input voltage:
GND pin current is found by examining the GND Pin Cur-
rent curves in the Typical Performance Characteristics
section. Power dissipation is equal to the sum of the two
components listed prior.
The LT3008 regulator has internal thermal limiting designed
to protect the device during overload conditions. For con-
tinuous normal conditions, do not exceed the maximum
junction temperature rating of 125°C. Carefully consider
all sources of thermal resistance from junction to ambi-
ent including other heat sources mounted in proximity to
the LT3008. For surface mount devices, heat sinking is
accomplished by using the heat spreading capabilities of
the PC board and its copper traces. Copper board stiffen-
ers and plated through-holes can also be used to spread
the heat generated by power devices.
differential: I
I
GND
• V
IN
OUT
• (V
IN
– V
OUT
)
3008f