S-8340A25AFT-T2-X Datasheet, PDF (21/55 Pages) Seiko Instruments Inc – SWITCHABLE SWITCHING REGULATOR CONTROLLER

STEP-UP, 600 kHz, PWM CONTROL OR PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.4.0_01
S-8340/8341 Series
VOUT
min.
=
(1+_RRFFBB21
min.
max.
) × 0.98 − ΔV [V]
RFB1 max.
VOUT max. = (1+_{RFB2 min.} ) × 102 + ΔV [V]
RFB1 and RFB2 must be adjusted in order to set the voltage accuracy of VOUT to the IC output voltage accuracy (VOUT
±2.0%) or lower. The smaller RFB1 and RFB2 are, the less VOUT is affected by the absolute value accuracy of RFB1
and RFB2. The smaller RFB1 and RFB2 are, the less VOUT is affected by IFB.
To reduce the influence due to IFB that affects variations of VOUT, the RFB2 value must be set to a value sufficiently
lower than the input impedance at the FB pin (1 V/50 nA = 20 MΩ (max.)).
Reactive current flows through RFB1 and RFB2. Unless the reactive current value is limited as low as possible with
respect to the actual load current, efficiency decreases. Therefore, RFB1 and RFB2 should be sufficiently large.
Caution If the RFB1 and RFB2 values are too large (1 MΩ or more), VOUT is subject to be affected by external
noise, therefore, thoroughly test the performance with the actual equipment.
Since the accuracy of VOUT and reactive current must be traded off, they must be considered according to
application requirements.
Caution
Connect the VDD pin to the VOUT pin for both the fixed output types and external setting types
as shown in “ Standard Circuit”. In the cases when VDD requires to be applied from VIN or
other power source instead of VOUT, raise VDD to 2.5 V or higher within the soft-start time (3.0 ms:
A and B types, 6.0 ms: C and D types).
When the VDD pin is connected to the VOUT pin, VIN can be increased slowly without any
problems.
The table below provides a rough guide for selecting a product type according to the application requirements of the
application.
Choose the product that gives you the largest number of circles (O).
Table 9
The set output voltage is 6 V or less
S-8340
S-8341
A
B
C
D
A
B
C
D
Set an output voltage freely
The efficiency under light loads (approx. 1mA) is an
important factor
To be operated with a medium load current (200 mA
class)
To be operated with a high load current (1 A class)
It is important to have a low-ripple voltage
Downsizing of external components is important







Remark The symbol " " denotes an indispensable condition, while the symbol "" indicates that the
corresponding series has superiority in that aspect. The symbol "" indicates particularly high
superiority.
21