S-8520 Seiko Instruments, S-8520 Datasheet - Page 15

• Manufacturer Part Number: S-8520
• Description: (S-8520 / S-8521) PWM Control and PFM Control Step DOwn Switching Regulator Controllers
• Manufacturer: Seiko Instruments

Rev.7.4
Application Circuits:
1. External adjustment of output voltage
the built-in electrostatic protection circuit.
Do not apply an electrostatic discharge to this IC that exceeds the performance ratings of
Seiko Instruments Inc. shall not be responsible for any patent infringement by products including the S-
8520/8521 Series in connection with the method of using the S-8520/8521 Series in such products, the
product specifications or the country of destination thereof.
The S-8520/21 Series allows you to adjust the output voltage or to set the output voltage to a value over
the preset output voltage range (6 V) of the products of this series, when external resistances R
and capacitor C
obtained by inserting a thermistor or other element in series with R
Therefore, the output voltage (OUT) is determined by the output voltage value V
Series, and the ratio of the parallel resistance value of external resistance R
+ R
The voltage accuracy of the output OUT set by resistances R
output voltage accuracy (V
R
Let us designate the maximum deviations of the absolute value of external resistances R
R
maximum and minimum deviations of the absolute value of internal resistances R
(R
maximum deviation value OUTmax of the output voltage OUT are expressed by the following equations:
The voltage accuracy of the output OUT cannot be made higher than the output voltage accuracy (V
2.4 %) of the IC itself, without adjusting the external resistances R
voltage value of the output OUT and the output voltage value (V
the more the output voltage remains immune to deviations in the absolute accuracy of externally
connected resistances R
In particular, to suppress the influence of deviations in internal resistances R
contributor to deviations in the output OUT, the external resistances R
smaller value than that of internal resistances R
pin, as shown in Figure 11.
The S-8520 and 21 Series have an internal impedance of R
_10
B
A
1
max and R
PWM Control & PWM/PFM Control Step-Down Switching Regulator-Controllers
in use and the absolute value deviations of internal resistances R
+R
2
OUT = V
OUTmin = V
OUTmax = V
of the IC, to external resistance R
2
)max and (R
OUT
B
max, respectively, the minimum deviations by R
C
OUT
+ V
OUT
are added, as illustrated in Figure 11. Moreover, a temperature gradient can be
OUT
× 0.976 + V
1
× 1.024 + V
+R
+
−
× R
2
A
) min, respectively. Then, the minimum deviation value OUTmin and the
ON/OFF
and R
OUT
A
÷ ( R
Seiko Instruments Inc.
V
±2.4 %), but also by the absolute precision of external resistances R
IN
OUT
B
OUT
and the absolute value of internal resistances R
B
Oscillation
Cirucuit
PWM or
Switched Control
Circuit
PWM/PFM-
// ( R
× 0.976 × R
EXT
× 1.024 × R
A
. The output voltage is expressed by the following equation:
1
S-8520/21 Series
+ R
Reference Voltage
Source with
Soft-Start
2
Figure 11
))
A
1
A
V
min ÷ ( R
max ÷ ( R
and R
(Note: // denotes a combined resistance in parallel.)
SS
--
+
2
in the IC.
B
max // ( R
B
R
R
min // ( R
1
2
1
V
and R
A
OUT
A
OUT
and R
min and R
A
and R
1
) of the IC are brought to one other,
1
1
A
2
and R
+ R
A
+ R
between the VOUT and the VSS
and R
and R
B
D1
2
is not only affected by the IC's
2
B
)max )
.
)min )
2
B
in the IC.
B
B
C
and internal resistances R
1
B
min, respectively, and the
C
must be limited to a much
and R
involved. The closer the
1
S-8520/8521 Series
and R
1
OUT
R
R
and R
2
A
B
in the IC, a major
of the S-8520/21
2
in the IC.
2
A
in the IC by
and R
OUT
+
−
A
A
OUT
, R
B
and
by
B
±
1
,
15