LTC1703I 查看數據表（PDF） - Linear Technology
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LTC1703I
Linear Technology
LTC1703I Datasheet PDF : 36 Pages
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LTC1703
APPLICATIO S I FOR ATIO
Table 1. VID Inputs and Corresponding Output Voltage for
Channel 1
CODE VID4 VID3 VID2 VID1 VID0 VOUT1
00000 GND GND GND GND GND
2.00V
00001 GND GND GND GND
Float
1.95V
00010 GND GND GND Float GND
1.90V
00011 GND GND GND Float
Float
1.85V
00100 GND GND Float GND GND
1.80V
00101 GND GND Float GND
Float
1.75V
00110 GND GND Float Float GND
1.70V
00111 GND GND Float Float
Float
1.65V
01000 GND Float GND GND GND
1.60V
01001 GND Float GND GND
Float
1.55V
01010 GND Float GND Float GND
1.50V
01011 GND Float GND Float
Float
1.45V
01100 GND Float Float GND GND
1.40V
01101 GND Float Float GND
Float
1.35V
01110 GND Float Float Float GND
1.30V
01111* GND Float Float Float
Float
1.25V
* 01111 and 11111 are defined by Intel to signify “no CPU.” The LTC1703
will generate the output voltages shown when these codes are selected.
regulated output voltages as low as 800mV without exter-
nal level shifting amplifiers.
The LTC1703’s synchronous switching logic transitions
automatically into Burst Mode operation, maximizing effi-
ciency with light loads. An onboard overvoltage (OV) fault
flag indicates when an OV fault has occurred. The OV flag
can be set to latch the device off when an OV fault has
occurred, or to automatically resume operation when the
fault is removed.
2-Step Conversion
“2-step” architectures use a primary regulator to convert
the input power source (batteries or AC line voltage) to an
intermediate supply voltage, often 5V. This intermediate
voltage is then converted to the low voltage, high current
supplies required by the system using a secondary regu-
lator— the LTC1703. 2-step conversion eliminates the
need for a single converter that converts a high input
voltage to a very low output voltage, often an awkward
design challenge. It also fits naturally into systems that
continue to use the 5V supply to power portions of their
circuitry, or have excess 5V capacity available as newer
8
CODE
10000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
11101
11110
11111*
VID4
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
VID3
GND
GND
GND
GND
GND
GND
GND
GND
Float
Float
Float
Float
Float
Float
Float
Float
VID2
GND
GND
GND
GND
Float
Float
Float
Float
GND
GND
GND
GND
Float
Float
Float
Float
VID1
GND
GND
Float
Float
GND
GND
Float
Float
GND
GND
Float
Float
GND
GND
Float
Float
VID0
GND
Float
GND
Float
GND
Float
GND
Float
GND
Float
GND
Float
GND
Float
GND
Float
VOUT1
1.275V
1.250V
1.225V
1.200V
1.175V
1.150V
1.125V
1.100V
1.075V
1.050V
1.025V
1.000V
0.975V
0.950V
0.925V
0.900V
circuit designs shift the current load to lower voltage
supplies.
Each regulator in a typical 2-step system maintains a
relatively low step-down ratio (5:1 or less), running at high
efficiency while maintaining a reasonable duty cycle. In
contrast, a regulator taking a single step from a high input
voltage to a 1.xV output must run at a very narrow duty
cycle, mandating trade-offs in external component values
while compromising efficiency and transient response.
The efficiency loss can exceed that of using a 2-step
solution (see the 2-Step Efficiency Calculation section and
Figure 10). Further complicating the calculation is the fact
that many systems draw a significant fraction of their total
power off the intermediate 5V supply, bypassing the low
voltage supply. 2-step solutions using the LTC1703 usu-
ally match or exceed the total system efficiency of single-
step solutions, and provide the additional benefits of
improved transient response, reduced PCB area and sim-
plified power trace routing.
2-step regulation can buy advantages in thermal manage-
ment as well. Power dissipation in the LTC1703 portion of
a 2-step circuit is lower than it would be in a typical 1-step
1703fa
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