TC1305(2001) View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
TC1305
(Rev.:2001)
(Rev.:2001)
Microchip Technology
TC1305 Datasheet PDF : 10 Pages
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Dual 150mA CMOS LDO With Select
ModeTM, Shutdown and Independent
RESET Output
TC1305
Turn On Response
The turn on response is defined as two separate re-
sponse categories, Wake Up Time (tWK) and Settling Time
(tS).
The TC1305 has a fast Wake Up Time (10µsec typical)
when released from shutdown. See Figure 2 for the Wake
Up Time designated as tWK. The Wake Up Time is defined
as the time it takes for the output to rise to 2% of the VOUT
value after being released from shutdown.
The total turn on response is defined as the Settling
Time (tS), see Figure 2. Settling Time (inclusive with tWK) is
defined as the condition when the output is within 2% of its
fully enabled value (40µsec typical) when released from
shutdown. The settling time of the output voltage is depen-
dent on load conditions and output capacitance on VOUT (RC
response).
VIH
SHDN
VIL
VOUT
tS
98%
2%
tWK
Figure 2: Wake Up Response Time
Thermal Considerations
Thermal Shutdown
Integrated thermal protection circuitry shuts the regula-
tor off when die temperature exceeds 160°C. The regulator
remains off until the die temperature drops to approximately
150°C.
on a single layer FR4 dielectric copper clad PC board.
PDMAX = (TJMAX – TAMAX)
JA
Where all terms are previously defined.
Equation 2.
Equation 1 can be used in conjunction with Equation 2
to ensure regulator thermal operation is within limits. For
example:
GIVEN:
VINMAX = 3.8V ± 5%
VOUT1MIN = 3.0V ± 2.5%
VOUT2MIN = 3.0V ± 2.5%
ILOAD1MAX = 120mA
ILOAD2MAX = 120mA
TJMAX = 125°C
TAMAX = 55°C
JA = 113°C/W
FIND:
1) Actual power dissipation:
PD ≈ [(VINMAX - VOUT1MIN) x ILOAD1MAX
+ [(VINMAX - VOUT2MIN) x ILOAD2MAX
[(3.8 x 1.05) - (3.0 x .975)] x 120 x 10-3
+ [(3.8 x 1.05) - (3.0 x .975)] x 120 x 10-3
= 256mW
2) Maximum allowable power dissipation:
PD ≈ (TJMAX– TAMAX)
JA
Power Dissipation
The amount of power the regulator dissipates is prima-
rily a function of input and output voltage, and output current.
The following equation is used to calculate worst case actual
power dissipation:
PD ≈ (VINMAX – VOUTMIN)ILOADMAX
Where:
PD = worst case actual power dissipation
VINMAX = maximum voltage on VIN
VOUTMIN = minimum regulator output voltage
ILOADMAX = maximum output (load) current
Equation 1.
The maximum allowable power dissipation (Equation 2)
is a function of the maximum ambient temperature (TAMAX),
the maximum allowable die temperature (125°C), and the
thermal resistance from junction-to-air (JA). The MSOP-10
package has a JA of approximately 113°C/W when mounted
= (125 – 55)
113
= 620mW
In this example, the TC1305 dissipates a maximum of
only 256mW; far below the allowable limit of 620mW. In a
similar manner, Equation 1 and Equation 2 can be used to
calculate maximum current and/or input voltage limits. For
example, the maximum allowable VIN is found by substitut-
ing the maximum allowable power dissipation of 620mW
into Equation 1, from which VINMAX = 5.3V.
Layout Considerations
The primary path of heat conduction out of the package
is via the package leads. Therefore, layouts having a ground
plane, wide traces at the pads, and wide power supply bus
lines combine to lower JA and, therefore, increase the
maximum allowable power dissipation limit.
© 2001 Microchip Technology Inc. DS21526A
5
TC1305-1 12/22/00
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