LTC2970 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2970' PDF : 36 Pages View PDF
LTC2970/LTC2970-1
APPLICATIO S I FOR ATIO
( ) VDC0,MAX
>
VDC0,NOM
+
R20
R30
•
VFB0 − 10mV
→
VDC0,MAX
>
2.631V
+
10kΩ
7.68kΩ
•
(0.8V − 10mV) = 3.660V
From Equation 7, the margining resolution will be less
than:
R20 •R40 • 276μA
VRES < R30 256
=
10kΩ • 6.65kΩ • 276μA
7.68kΩ
= 9.33mV/LSB
256
Margining DC/DC Converter with TRIM Pin Design
Example
The output voltage of the DC/DC converter in Figure 2 needs
to be margined ±10% about its nominal value. Assume
that RTRIM = 10.22kΩ and VREF = 1.225V.
1. Solve for R30 using Equation 10:
R30
≤
RTRIM
•
⎛
⎝⎜
50 − ΔDOWN%⎞
ΔDOWN% ⎠⎟
=
10.22kΩ
•
⎛
⎝⎜
50 − 10⎞
10 ⎠⎟
=
40,880Ω
Let R30 = 39.2kΩ.
2. Solve for R40 using Equations 11:
R40
≥
⎛
⎝⎜ 1+
ΔUP% ⎞
ΔDOWN % ⎠⎟
•
VREF
236μA
=
⎛
⎝⎜
1+
10⎞
1 0 ⎠⎟
•
1.225V
236μA
=
10,381Ω
Let R40 = 10.5kΩ.
32
Tracking Application Circuit Design Example
Consider the LTC2970-1 application circuit shown in Figure
3. Channel 0 is a 1.8V DC/DC converter while channel 1
is a 2.5V switching power supply. Both converters have
a feedback node voltage of 0.8V and need to track on and
off coincidentally. In addition, a margin range of +5% and
–10% is required for each supply.
1. Assume a value for R20 and solve for R21.
Let R20 = 5,970Ω. From Equation 12:
R21= R20 • VDC1,NOM = 5,970Ω • 2.5V = 8,292Ω
VDC0,NOM
1.8V
Let R21 = 8,250Ω (the nearest E192 Series resistor
value).
2. Solve for R10 and R11.
From Equation 13:
R10 =
⎛
⎝⎜
R20
VDC0,NOM
VFB0
⎞
− 1⎠⎟
=
⎛
⎝⎜
5,970Ω
1.8V
0.8V
−
1⎞⎠⎟
=
4,776Ω
R11=
R21
= 8,250Ω = 3,882Ω
⎛
⎝⎜
VDC1,NOM
VFB1
⎞
− 1⎠⎟
⎛
⎝⎜
2.5V
0.8V
−
1⎞⎠⎟
Let R10 = 4,750Ω and R11 = 3,880Ω.
3. Solve for R40 and R41.
Assume that R40 = R41.
R40 = R41≥
⎛
(( )) VFBn • ⎝⎜⎜
VDCn,NOM − VDCn,MIN
VDCn,MAX − VDCn,NOM
⎞
+ 1⎠⎟⎟ + 10mV =
236μA
0.8V
•
⎛
⎝⎜
(1− 0.9)
(1.05 − 1)
+
1⎞⎠⎟
+
10mV
=
10,212Ω
236μA
Let R40 = R41 = 10.5kΩ
29701fc
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