S8353 datasheet(21/49 Pages) SII

21 / 49 page

STEP-UP, PWM CONTROL or PWM / PFM SWITCHABLE BUILT-IN TRANSISTOR SWITCHING REGULATOR

Rev.3.0_01

S-8353/8354 Series

3. Capacitor (CIN, CL)

A capacitor on the input side (CIN) improves the efficiency by reducing the power impedance and stabilizing the input

current. Select a CIN value according to the impedance of the power supply used.

A capacitor on the output side (CL) is used for smoothing the output voltage. For step-up types, the output voltage

flows intermittently to the load current, so step-up types need a larger capacitance than step-down types. Therefore,

select an appropriate capacitor in accordance with the ripple voltage, which increases in case of a higher output

voltage or a higher load current. The capacitor value should be 10

μF or more.

Select an appropriate capacitor the equivalent series resistance (RESR) for stable output voltage. The stable voltage

range in this IC depends on the RESR. Although the inductance value (L value) is also a factor, an RESR of 30

500 m

Ω maximizes the characteristics. However, the best RESR value may depend on the L value, the capacitance,

the wiring, and the applications (output load).

Therefore, fully evaluate the RESR under the actual operating

conditions to determine the best value.

Refer to the “1. Example of Ceramic Capacitor Application” (Figure 16) in the “ Application Circuit” for the

circuit example using a ceramic capacitor and the external resistance of the capacitor (RESR).

4. VDD / VOUT Separate Type (D and J Types)

The D and J types provides separate internal circuit power supply (VDD pin) and output voltage setting pin (VOUT

pin) in the IC, making it ideal for the following applications.

(1) When changing the output voltage with external resistance.

(2) When outputting a high voltage within the operating voltage (10 V).

Choose the products in the Table 18 according to the applications (1) or (2) above.

Table 18

Output voltage (VCC)

1.8 V

≤ VCC < 5 V

5 V

≤ VCC ≤ 10 V

S-835xx18

Yes

−

S-835xx50

−

Yes

Connection to VDD pin

VIN or VCC

VIN

Cautions 1. This IC starts a step-up operation at VDD = 0.8 V, but set 1.8

≤ VDD ≤ 10 V to stabilize the output

voltage and frequency of the oscillator. (Input a voltage of 1.8 V or more at the VDD pin for all

products with a setting less than 1.9 V.) An input voltage of 1.8 V or more at the VDD pin allows

connection of the VDD pin to either the input voltage VIN pin or output VOUT pin.

2. Choose external resistors RA and RB so as to not affect the output voltage, considering that there

is impedance between the VOUT pin and VSS pin in the IC chip. The internal resistance

between the VOUT pin and VSS pin is as follows :

(1) S-835xx18 : 2.1 M

Ω to 14.8 MΩ

(2) S-835xx20 : 1.4 M

Ω to 14.8 MΩ

(3) S-835xx30 : 1.4 M

Ω to 14.2 MΩ

(4) S-835xx50 : 1.4 M

Ω to 12.1 MΩ

3. Attach a capacitor (CC) in parallel to the RA resistance when an unstable event such as

oscillation of the output voltage occurs. Calculate CC using the following equation :

[]

kHz

•

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