LTC1703IG#TR Linear Technology, LTC1703IG#TR Datasheet - Page 24

• Manufacturer Part Number: LTC1703IG#TR
• Description: IC CTLR REG SW DUAL 2PH 28-SSOP
• Manufacturer: Linear Technology

Specifications of LTC1703IG#TR

• Applications: Controller, Mobile Intel Pentium® III
• Voltage - Input: 3 ~ 7 V
• Number Of Outputs: 2
• Voltage - Output: 0.9 ~ 2 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
LTC1703
Now calculate the remaining values:
(K is a constant used in the calculations)
ƒ = chosen crossover frequency
G = 10
gain)
Type 2 Loop:
Type 3 Loop:
24
K Tan
R
R
K Tan
R
R
R
C
C
C
C
C
2
1
2
1
3
2
B
2
3
B
=
=
=
=
=
=
=
=
=
=
(GAIN/20)
=
=
C K
C K
2
2
2
2
2
( )
V
V
2
2
K
πƒ
πƒ
πƒ
πƒ
OUT
πƒ
OUT
( )
V
( )
R
V
⎛
⎜
⎝
K
2
–
REF
REF
K
1
⎛
⎜
⎝
1
BOOST
GKR
GR
C
C
1
2
1
–
1
BOOST
1
1
–
K R
–
–
(this converts GAIN in dB to G in absolute
1
( )
( )
2
1
R
R
V
V
1
4
1
1
REF
1
REF
3
U
+
+
45
45
°
U
⎞
⎟
⎠
°
⎞
⎟
⎠
W
U
CURRENT LIMIT PROGRAMMING
Programming the current limit on the LTC1703 is straight-
forward. The I
maximum allowable voltage drop across QB (the bottom
MOSFET) before the current limit circuit engages. The
voltage across QB is set by its on-resistance and the
current flowing in the inductor, which is the same as the
output current. The LTC1703 current limit circuit inverts
the voltage at I
voltage across QB, allowing the current limit to be set with
a positive voltage.
To set the current limit, calculate the expected voltage
drop across QB at the maximum desired current:
I
expected operating current, to allow for MOSFET R
changes with temperature. Setting I
maximum normal operating current is usually safe and will
adequately protect the power components if they are
chosen properly. The CF term is an approximate factor that
corrects for errors caused by ringing on the switch node
(illustrated in Figure 6). This correction factor will change
depending on the layout and the components used, but
100mV is usually a good starting point. However, to
provide adequate margin and to accommodate for offsets
and external variations, it is recommended that V
calculated with CF = 100 ± 50mV. V
grammed at the I
and an external resistor:
The resulting value of R
circuit to ensure that the I
MOSFET R
automobiles, and should be taken with a grain of salt.
Circuits that use very low values for R
be checked carefully, since small changes in R
cause large I
factor makes up a large percentage of the total V
value. If V
start up.
LIM
V
R
PROG
ILIM
should be chosen to be quite a bit higher than the
= V
= (I
PROG
DS(ON)
PROG
ILIM
LIM
MAX
MAX
is set too low, the LTC1703 may fail to
)(R
/10µA
MAX
changes when the 100mV correction
pin sets the current limit by setting the
specs are like horsepower ratings in
before comparing it with the negative
DS(ON)
pin using the internal 10µA pull-up
ILIM
LIM
) + CF
should be checked in an actual
circuit kicks in as expected.
LIM
IMAX
PROG
to 150% of the
(< 20k) should
is then pro-
IMAX
PROG
DS(ON)
PROG
1703fa
can
be