s-8337aaca-t8t1g Seiko Instruments Inc., s-8337aaca-t8t1g Datasheet - Page 19

• Manufacturer Part Number: s-8337aaca-t8t1g
• Description: Step-up, 1.2 Mhz High-frequency, Pwm Control Switching Regulator Controller
• Manufacturer: Seiko Instruments Inc.

Rev.3.1
5. Oscillation frequency and maximum duty ratio setting resistors (ROSC, RDuty)
With the S-8337/8338 Series, the oscillation frequency can be set in a range of 286 kHz to 1.133 MHz
using external resistance. Connect a resistor across the ROSC and VSS pins. Select the resistor by
using the following equation and referring to Figure 12 . However, the following equation and figure
assume that the resistance value is the desired value and show the theoretical values when the IC is
in the typical conditions. Note that fluctuations of resistance and IC are not considered.
With the S-8337 Series, the maximum duty ratio can be set in a range of 47% to 88.5% by an external
resistor. Connect the resistor across the RDuty and VSS pins. Select the resistance by using the
following equation and referring to Figure 13 . The maximum duty ratio fluctuates according to the
oscillation frequency. If the value of ROSC is changed, therefore, be sure to change the value of
RDuty so that it is always in proportion to ROSC. However, the following equation and figure assume
that the resistance value is the desired value and show the theoretical values when the IC is in the
typical conditions. Note that fluctuations of resistance and IC are not considered.
Connect resistors ROSC and RDuty as close to the IC as possible.
R
_00
R
R
OSC
STEP-UP, 1.2 MHz HIGH-FREQUENCY, PWM CONTROL SWITCHING REGULATOR CONTROLLER
OSC
Duty
[kΩ] ≅
≅
(94.5 − MaxDuty)
f
140
OSC
11.5
[kHz]
•
10
3
Seiko Instruments Inc.
1400
1200
1000
800
600
400
200
100
90
80
70
60
50
40
0
0
0
Figure 13 R
Figure 12 R
1
200
Duty
R
R
Duty
2
OSC
/R
/R
[kΩ]
OSC
OSC
OSC
S-8337/8338 Series
3
vs. f
vs. MaxDuty
400
OSC
4
600
5
19