S-9365AAAAAI6TIG2 SII [Seiko Instruments Inc], S-9365AAAAAI6TIG2 Datasheet - Page 17

• Manufacturer Part Number: S-9365AAAAAI6TIG2
• Description: STEP-UP, SUPER-SMALL PACKAGE, 1.2 MHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
• Manufacturer: SII [Seiko Instruments Inc]

Rev.1.1
STEP-UP, SUPER-SMALL PACKAGE, 1.2 MHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Operation Principles
The S-8365/8366 Series is a step-up switching regulator controller. Figure 14 shows the basic circuit diagram.
Step-up switching regulators start current supply by the input voltage (V
on and holds energy in the inductor at the same time. When the Nch power MOS FET is turned off, the CONT pin
voltage is stepped up to discharge the energy held in the inductor and the current is discharged to V
diode. When the discharged current is stored in C
the voltage of the FB pin reaches the same potential as the internal reference voltage.
For the PWM control method, the switching frequency (f
according to the ratio of the ON time and OFF time (ON duty) of the Nch power MOS FET in each period.
For the PWM control method, the V
In the S-8366 Series, the Nch power MOS FET is turned on when the fixed duty cycle is 28% for the PFM control
method. When energy is discharged to V
MOS FET stays in the off status until V
decreases to the set value or less depends on the amount of load current, so, the switching frequency varies
depending on this current.
The ON duty in the current continuous mode can be calculated by using the equation below. Use the S-8365/8366
Series in the range where the ON duty is less than the maximum duty. Note that the products with short-circuit
protection is set in the timer-latch status if the maximum duty lasts the short-circuit protection delay time (t
more.
The maximum duty is 85% typ. for 1.2 MHz products and 90% for 600 kHz products.
The ON time (t
ON duty =
t
*1. V
ON
_00
=
=
D
f
: Forward voltage of diode
f
OSC
OSC
1
1


1 −
×
× ON duty
ON


) can be calculated by using the following equation :
1 −
V
V
IN
OUT +
V
V
IN
OUT
V
Nch power
MOS FET
Figure 14 Basic Circuit of Step-up Switching Regulator
V
D
*1
+ V
IN
L


D
× 100 [%]
*1
I
1


OUT
·········· (1)
CONT
voltage is held constant by controlling the ON time.
OUT
OUT
Seiko Instruments Inc.
decreases to the set value or less due to the load discharge. Time V
once and the V
SD
EXT
L
, a voltage is generated, and the potential of V
VSS
OSC
I
2
OUT
) is fixed and the V
FB
potential exceeds the set value, the Nch power
IN
V
) when the Nch power MOS FET is turned
OUT
C
OUT
OUT
S-8365/8366 Series
voltage is held constant
R
I
L
OUT
OUT
OUT
increases until
through the
PRO
) or
OUT
17