S-8353A20MC-IQFT2X Datasheet, PDF (21/49 Pages) Seiko Instruments Inc – BUILT-IN TRANSISTOR SWITCHING REGULATOR

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 to
500 mΩ 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.
Output voltage (VCC)
S-835xx18
S-835xx50
Connection to VDD pin
Table 18
1.8 V ≤ VCC < 5 V
Yes
−
VIN or VCC
5 V ≤ VCC ≤ 10 V
−
Yes
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 MΩ to 14.8 MΩ
(2) S-835xx20 : 1.4 MΩ to 14.8 MΩ
(3) S-835xx30 : 1.4 MΩ to 14.2 MΩ
(4) S-835xx50 : 1.4 MΩ 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 :
C_C
[
F
]=
2
•
π
1
•R_A •
20
kHz
21