Datasheet

23
LTC1735
1735fc
APPLICATIO S I FOR ATIO
WUU
U
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
C
OSC
RUN/SS
I
TH
FCB
SGND
V
OSENSE
SENSE
–
SENSE
+
TG
BOOST
SW
V
IN
INTV
CC
BG
PGND
EXTV
CC
U1
LTC1735
C2
0.1µF
C8
0.22µF
C4
100pF
C5
47pF
C3
100pF
R2
100k
R1
27k
R5
0.003Ω
GND
V
OUT
1.5V
15A
V
IN
7.5V TO
24V
GND
C6
1000pF
C1
39pF
+
C10
4.7µF
10V
C9
1µF
5V (OPTIONAL)
C11
330pF
C19
1µF
+
C15 TO
C18
180µF
4V
C7
0.1µF
M1
FDS6680A
M2, M3
FDS6680A
×2
C9, C19: TAIYO YUDEN JMK107BJ105
C10: KEMET T494A475M010AS
C12 TO C14: TAIYO YUDEN GMK325F106
C15 TO C18: PANASONIC EEFUE0G181R
D1: CENTRAL SEMI CMDSH-3
D2: MOTOROLA MBRS340
L1: PANASONIC ETQP6F1R0SA
M1 TO M3: FAIRCHILD FDS6680A
R5: IRC LRF2512-01-R003-J
U1: LINEAR TECHNOLOGY LTC1735CS
1735 F08
D1
CMDSH-3
R6
10k
R7
11.5k
D2
MBRS340
C12 TO C14
10µF
35V
L1
1µH
R4
100k
R3
680k
Figure 8. CPU-Core-Voltage Regulator with Active Voltage Positioning
voltage cannot exceed ±0.082V. At V
OUT
= 1.5V, the
maximum output voltage change controlled by the I
TH
pin
would be:
∆=
=
±
=±
V
Input Offset V
V
V
V
mV
OSENSE
OUT
REF
•
.•.
.
003 15
08
56
With the optimum resistor values at the I
TH
pin, the output
voltage will swing from 1.55V at minimum load to 1.44V
at full load. At this output voltage, active voltage position-
ing provides an additional ±56mV to the allowable tran-
sient voltage on the output capacitors, a 68% improve-
ment over the ±82mV allowed without active voltage
positioning.
The next step is to calculate the scale factor for V
ITH
, the
I
TH
pin voltage. The V
ITH
scale factor reflects the I
TH
pin
voltage required for a given load current. V
ITH
controls the
peak sense resistor voltage, which represents the DC
output current plus one half of the peak-to-peak inductor
current. The no load to full load V
ITH
range is from 0.3V to
2.4V, which controls the sense resistor voltage from 0V to
the ∆V
SENSE(MAX)
voltage of 75mV. The calculated V
ITH
scale factor with a 0.003Ω sense resistor is:
V ScaleFactor
V Range Sense sistor Value
V
VV
V
VA
ITH
ITH
SENSE MAX
=
∆
==
•Re
(. – . )• .
.
./
()
24 03 0003
0 075
0 084
V
ITH
at any load current is:
VI
I
V ScaleFactor
V Offset
ITH OUTDC
L
ITH
ITH
=+
∆












+
2
•