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PDF TC1267 Data sheet ( Hoja de datos )
| Número de pieza | TC1267 | |
| Descripción | 400mA PCI LDO | |
| Fabricantes | Microchip Technology | |
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TC1267
400mA PCI LDO
Features
• Glitch Free Transition Between Input Sources
• Automatic Input Source Selection
• External PMOS Bypass Switch Control
• Built-in 5V Detector
• 1% Regulated Output Voltage Accuracy
• 400mA Load Current Capability
• Kelvin Sense Input
• Low Ground Current, Independent of Load
Applications
• PCMCIA
• PCI
• Network Interface Cards (NICs)
• CardbusTM Technology
• Desktop Computers
Device Selection Table
Part Number
TC1267VET
Package
5-Pin DDPAK
Junction
Temp. Range
-5°C to +95°C
Pin Configuration
5-Pin DDPAK
Tab is GND
TC1267
1 234 5
General Description
The TC1267 is an application-specific, low dropout
regulator (LDO), specifically intended for use in PCI
peripheral card applications complying with PCI Power
Management (PCI 2.0). It provides an uninterrupted,
3.3V output voltage when the main (5V) or auxiliary
(3.3V) input voltage supplies are present.
The TC1267 consists of an LDO, a voltage threshold
detector, external switchover logic and gate drive
circuitry. It functions as a conventional LDO as long as
the voltage on the main supply input (VIN) is above the
lower threshold (3.90V typical). Should the voltage on
VIN fall below the lower threshold, the LDO is disabled
and an external P-channel MOSFET is automatically
turned on, connecting the auxiliary supply input to
VOUT, and ensuring an uninterrupted 3.3V output. The
main supply is automatically selected, if both the main
and auxiliary input supplies are present, and transition
from one input supply to the other is ensured glitch-
free. High integration, automatic secondary supply
switchover, Kelvin sensing, and small size make the
TC1267 the optimum LDO for PCI 2.0 applications.
Functional Block Diagram
VIN
VAUX
Detect
GND
Bandgap
Reference
–
E/A
+
DR
VOUT
© 2002 Microchip Technology Inc.
DS21378B-page 1
1 page  
4.0 THERMAL CONSIDERATIONS
4.1 Thermal Shutdown
Integrated thermal protection circuitry shuts the
regulator off when die temperature exceeds 160°C.
The regulator remains off until the die temperature
drops to approximately 150°C.
4.2 Power Dissipation
The amount of power the regulator dissipates is
primarily a function of input and output voltage, and
output current. The following equation is used to
calculate worst case actual power dissipation:
EQUATION 4-1:
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
The maximum allowable power dissipation
(Equation 4-2) is a function of the maximum ambient
temperature (TAMAX), the maximum allowable die
temperature (TJMAX) and the thermal resistance from
junction-to-air (θJA).
EQUATION 4-2:
PDMAX = (TJMAX – TAMAX)
θJA
Where all terms are previously defined.
Table 4-1 shows various values of θJA for the TC1267
packages.
TABLE 4-1:
THERMAL RESISTANCE
GUIDELINES FOR TC1267 IN
5-PIN DDPAK
Copper
Area
(Topside)*
Copper
Area
(Backside)
Board
Area
Thermal
Resistance
(θJA)
2500 sq mm 2500 sq mm 2500 sq mm 25°C/W
1000 sq mm 2500 sq mm 2500 sq mm 27°C/W
125 sq mm 2500 sq mm 2500 sq mm 35°C/W
*Tab of device attached to topside copper.
TC1267
Equation 4-1 can be used in conjunction with
Equation 4-2 to ensure regulator thermal operation is
within limits. For example:
Given:
VINMAX = 5V ± 5%
VOUTMIN = 3.217V
ILOADMAX = 400mA
TJMAX = 95°C
TAMAX = 70°C
θJA = 27°C/W (DDPAK mounted on
1000 sq mm topside copper area)
Find: 1. Actual power dissipation
2. Maximum allowable dissipation
Actual power dissipation:
PD ≈ (VINMAX – VOUTMIN)ILOADMAX
= (5.25V - 3.217V) 400mA
= 813mW
Maximum allowable power dissipation:
PDMAX = (TJMAX – TAMAX)
θJA
= (95 – 70)
27
= 423mW
In this example, the TC1267 dissipates a maximum of
813mW; below the allowable limit of 926mW.
© 2002 Microchip Technology Inc.
DS21378B-page 5
5 Page 
TC1267
SALES AND SUPPORT
Data Sheets
Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recom-
mended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following:
1. Your local Microchip sales office
2. The Microchip Corporate Literature Center U.S. FAX: (480) 792-7277
3. The Microchip Worldwide Site (www.microchip.com)
Please specify which device, revision of silicon and Data Sheet (include Literature #) you are using.
New Customer Notification System
Register on our web site (www.microchip.com/cn) to receive the most current information on our products.
2002 Microchip Technology Inc.
DS21378B-page 11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet TC1267.PDF ] | |
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