S8340 datasheet(21/55 Pages) SII

21 / 55 page

STEP-UP, 600 kHz, PWM CONTROL OR PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER

Rev.4.0_01

S-8340/8341 Series

VOUT min.

= (1+

)

× 0.98 − ΔV [V]

VOUT max.

= (1+

)

× 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 M

Ω 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

S-8340

S-8341

The set output voltage is 6 V or less

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.

RFB1 min.

RFB2 max.

RFB1 max.

RFB2 min.

S8340 Datasheet(PDF) 21 Page - Seiko Instruments Inc

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