LTC2970-1 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2970-1' PDF : 36 Pages View PDF
LTC2970/LTC2970-1
APPLICATIO S I FOR ATIO
4. Solve for R30B and R31B.
( ) R30B ≤
R40 • 236μA − VFB0 − 0.8V − 10mV
VFB0
•
⎛
⎝⎜
1
R10
+
1
R20
⎞
⎠⎟
=
(10.5kΩ • 236μA − 0.8V
0.8V
•
⎛
⎝⎜
1
4,750Ω
+
− 0.8V − 10mV)
1⎞
5,970Ω ⎠⎟
=
2,870Ω
R31B
≤
(R41•
236μA −
VFB1
•
⎛
⎝⎜
VFB1 −
1+
R11
0.8V −
1⎞
R21⎠⎟
10mV
)
=
(10.5kΩ • 236μA − 0.8V − 0.8V − 10mV) = 2,863Ω
0.8V
•
⎛
⎝⎜
1
3,880Ω
+
1
8,250Ω
⎞
⎠⎟
For coincident tracking to occur Equation 17 also must
be satisfied:
R30B = R31B
R20 R21
→R30B = R31B •R20 = 2,863Ω • 5,970Ω = 2,078Ω
R21
8,250Ω
→R31B = R30B •R21= 2,870Ω • 8,250Ω = 3,957Ω
R20
5,970Ω
Let R30B = 2,100Ω and R31B = 2,890Ω.
5. Solve for R30A and R31A.
Referring to Equation 18:
R30A ≤
R20
− R30B =
⎛
⎝⎜
1+
R20
R10
⎞
⎠⎟
•
⎛
⎝⎜
VDC0,MAX − VDC0,NOM
VDC0,NOM
⎞
⎠⎟
5,970Ω
− 2,100Ω = 50,806Ω
⎛
⎝⎜
1+
5,970Ω
4,750Ω
⎞
⎟⎠
•
⎛
⎝⎜
1.05 −
1
1⎞
⎠⎟
R31A ≤
R21
− R31B =
⎛
⎝⎜
1+
R21⎞
R11⎠⎟
•
⎛
⎝⎜
VDC1,MAX − VDC1,NOM
VDC1,NOM
⎞
⎠⎟
8,250Ω
− 2,890Ω = 49,888Ω
⎛
⎝⎜
1+
8,250Ω
3,880Ω
⎞
⎟⎠
•
⎛
⎝⎜
1.05
1
−
1⎞
⎠⎟
Let R30A = 49.9kΩ and R31A = 48.7kΩ.
6. Solve for Channel 1’s tracking counter delay relative to
Channel 0, CH1_A_DELAY_TRACK().
First, recalculate the values of VDCn,NOM based on the final
values of R1n and R2n:
VDC0,NOM′
=
VFB
•
⎛
⎝⎜
1+
R20
R10
⎞
⎠⎟
+ IFB
• R20
=
0.8V •
⎛
⎝⎜
1+
5,970Ω ⎞
4,750Ω ⎠⎟
+
0
=
1.805V
VDC1,NOM′
=
0.8V
•
⎛
⎝⎜
1+
8,250Ω
3,880Ω
⎞
⎠⎟
+
0
=
2.501V
Next, apply Equation 19:
CH1_ A _DELAY _ TRACK() =
( ) VDC1,NOM′ − VDC0,NOM′
• R31B
R21 =
1μA / count •R41
(2.501V
−
1.805V)
•
2,890Ω
8,250Ω
=
23counts
1μA / count • 10.5kΩ
7. Solve for the IDAC0 and IDAC1 terminal tracking codes,
Chn_a_idac_track[7:0].
Ch0 _ a _ idac[7:0]= Ch1_ a _ idac[7:0]=
255 −
0.8V
= 179
1μA / LSB• 10.5kΩ
29701fc
33
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