S-8541 Seiko Instruments, S-8541 Datasheet - Page 21

• Manufacturer Part Number: S-8541
• Description: (S-8540 / S-8541) 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
• Manufacturer: Seiko Instruments

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Rev.3.2
STEP-DOWN, 600 kHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
e.g. When V
R
capacitor (C
Set the C
The precision of output voltage (V
the FB pin (1 V ± 2.0%), the precision of R
voltage V
Suppose that the FB pin input current is 0 nA, and that the maximum absolute values of the external
resistors R
R
dependency is Δ V, the minimum value V
V
The precision of the output voltage V
without adjustment of external resistors R
absolute value precision of the external resistors R
affected by the FB pin input current.
To suppress the influence of FB pin input current on the variation of output voltage V
resistor R
20 M Ω max.
Waste current flows through external resistors R
to load current in actual use, the efficiency decreases. The R
must therefore be made sufficiently high.
Evaluation of the influence of the noise is needed in the actual condition If the R
resistors are high (1 M Ω or higher) since they are susceptible to external noise.
The output voltage V
considered according to application requests.
OUT
A
A
, R
and R
_00
variation is calculated by the following formula:
B
must be R
V
V
OUT
OUT
DD
FB
B
B
A
value must be made sufficiently lower than the input impedance of the FB pin, 1 V/50 nA =
.
min. = ( 1 +
max. = ( 1 +
so that f = 1/(2 × π C
FB
and R
are
OUT
) in parallel to R
A
= 3.0 V, R
B
+ R
R
are R
A
OUT
B
R
R
R max.
min. and R
R min.
≤ 2 M Ω and the ratio of R
B
A
A
B
max.
min.
A
precision and the waste current are in a trade-off relation. They must be
A
max. and R
= 200 k Ω , R
A
) × 0.98 − Δ V [ V ]
to prevent unstable operation like output oscillation.
) × 1.02 + Δ V [ V ]
FB
 × R
OUT
B
OUT
) determined by R
A
min., and that the output voltage shift due to the V
) is 0.1 to 20 kHz (normally 10 kHz).
B
Seiko Instruments Inc.
cannot be made lower than the precision of the IC output voltage
B
max, and the minimum absolute values of the external resistors
OUT
A
= 100 k Ω , then C
and R
A
min. and maximum value V
and R
A
A
and R
B
to R
. The lower the R
A
B
, current input to the FB pin, and IC power supply
and R
B
A
, R
B
should be set so that the FB pin is 1.0 V. Add a
. When it is not a negligible value with respect
B
FB
B
is affected by the precision of the voltage at
. The lower the R
= 100 pF.
A
and R
A
B
/R
values of the external resistors
B
OUT
, the less it is affected by the
max. of the output voltage
S-8540/8541 Series
A
and R
A
and R
OUT
B
, the less it is
, the external
B
DD
values of
voltage
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