Datasheet
LTC2970/LTC2970-1
31
29701fc
APPLICATIO S I FOR ATIO
WUU
U
6. Solve for Channel 1’s tracking counter delay relative to
Channel 0, CH1_A_DELAY_TRACK().
CH A DELAY TRACK
VV
R
DC NOM DC NOM
1
10
__ _ ()
,,
=
′
−
′
()
•
331
21
141
B
R
A count R
counts
μ /
()
•
(19)
Note: V
DCn,NOM
ʹ is based on the fi nal values of R2n and
R1n. If the result for CH1_A_DELAY_TRACK() is less than
0, apply the unsigned result to the CH0_A_DELAY_TRACK()
register.
7. Solve for the IDAC0 and IDAC1 terminal tracking codes,
Chn_a_idac_track[7:0].
Ch a idac track
V
ALSBR
L
FB
n
n
n
__ _ [:]
/
(
70
255
14
=
−
•μ
SSB s’)
(20)
Note: This formula assumes that the Chn_a_idac_pol bit
is set to 0.
Margining Application Circuit Design Example
Consider the LTC2970 application circuit shown in Figure
1. Channel 0 is a DC/DC converter whose output needs
to be varied between 3.63V and 1.62V. V
FB0
= 0.8V and
assume that I
FB0
= 0A.
1. Assume values for feedback resistor R20 and the
nominal DC/DC converter output voltage V
DC0,NOM
, and
solve for R10.
Let V
DC0,NOM
= 2.625V (the average of 3.63V and 1.62V)
and assume that R20 = 10kΩ. From Equation 1:
R
RV
VIRV
kV
FB
DC NOM FB FB
10
20
20
10 0 8
0
00
=
•
−•−
=
•
,
.Ω
22 625 0 8
4 384
..
,
VV−
=Ω
Let R10 = 4.37kΩ (the nearest E192 series resistor
value).
2. Solve for the value of R30 that yields the maximum
required DC/DC converter output voltage V
DC0,MAX
From Equation 2:
R
RV mV
VV
k
FB
DC MAX DC NOM
30
20 10
10 0 0
≤
•−
()
−
=
•
,,
..Ω 8810
3 63 2 625
7 861
VmV
VV
−
()
−
=
..
, Ω
Let R30 = 7.68kΩ.
3. Solve for the value of R40 that’s needed to yield the
minimum required DC/DC converter output voltage
V
DC0,MIN
.
From Equation 3:
R
VV
R
R
V
A
DC NOM DC MIN FB
40
30
20
236
2 625
≥
−
()
•+
=
,,
.
μ
VVV
k
k
V
A
−
()
•+
=
162
796
10
08
236
6 780
.
.
.
,
Ω
Ω
Ω
μ
Let R40 = 6.81kΩ.
4. Re-calculate the minimum, nominal, and maximum
DC/DC converter output voltages and the resulting mar-
gining resolution.
From Equations 4, 5, and 6:
VV
R
R
IR
V
DC NOM FB FB0
1
20
10
20
08 1
,
.
=•+
⎛
⎝
⎜
⎞
⎠
⎟
+• =
•+
110
437
2 631
k
k
V
Ω
Ω.
.
⎛
⎝
⎜
⎞
⎠
⎟
=
VV
R
R
AR V
DC MIN DC NOM FB00 0
20
30
236 40
,,
<−••−
()
μ
→<−•
•−
VV
k
k
Ak
DC MIN0
2 631
10
768
236 6 81 0
,
.
.
..
Ω
Ω
Ωμ 8810 159VmV V−
()
= .