R2J20701NP_08 RENESAS [Renesas Technology Corp], R2J20701NP_08 Datasheet - Page 17

• Manufacturer Part Number: R2J20701NP_08
• Description: Peak Current Mode Synchronous Buck Controller with Power MOS FETs
• Manufacturer: RENESAS [Renesas Technology Corp]

R2J20701NP
Study of Vout Accuracy
The nominal output voltage is calculated as
Here, the typical feedback voltage is 0.6 V.
The accuracy of Vout is strongly dependent on the variation of VFB, R1 and R2. VFB has a variation of 1% and
resistance intrinsically has a certain variation. When we take the variation in resistance into account, equation (6) is
extended to produce equation (7).
Here, K1 and K2 are coefficients. Both are 1.00 in the ideal case.
By equation (6), R1 is chosen as
Substituting this expression for R1 into equation (7) yields the following.
Therefore, variation in Vout is expressed as
REJ03G1459-0400 Rev.4.00 Jun 30, 2008
Page 17 of 27
Vout = VFB × (R1 + R2) / R2 ……(6)
Vout =
R1 =
Vout = VFB
Vout (typical)
Vout
=
Vout (typical)
VFB (typical)
R1
R1
R2
K1 + R2
K1 / K2 + R2
R2
=
K2
Vout (typical)
VFB (typical)
R
C
Vout (typical)
K2
1
VFB
VFB
VFB
R2
TRK-SS
REG5
1
CT
(7)
Vout (typical)
VFB (typical)
(8)
K1
K2
FB
+ 1
SW
1
(9)
K1
K2
+ 1
Vout
R1
R2
1
100 (%)
(10)