S-8337AAAA-P8T1G Datasheet, PDF (15/51 Pages) Seiko Instruments Inc – SWITCHING REGULATOR CONTROLLER

STEP-UP, 1.2 MHz HIGH-FREQUENCY, PWM CONTROL SWITCHING REGULATOR CONTROLLER
Rev.4.0_01
S-8337/8338 Series
Change in current (IL) flowing through the diode into VOUT during tOFF:
dlL
dt
=
VL
L
=
VOUT + VD −
L
VIN
…………………………………………………………..…………………(6)
Integration of the above equation is as follows:
IL
=
IPK
−


VOUT
+
VD
L
−
VIN


•
t
…………………………………………………………………………(7)
During tON, energy is stored in L and is not transmitted to VOUT. When receiving output current (IOUT)
from VOUT, the energy of the capacitor (CL) is used. As a result, the pin voltage of CL is reduced, and
goes to the lowest level after M1 is turned ON (tON). When M1 is turned OFF, the energy stored in L is
transmitted via the diode to CL, and the pin voltage of CL rises drastically. Because VOUT is a time
function indicating the maximum value (ripple voltage: Vp-p) when the current flowing through the
diode into VOUT and the load current IOUT match.
Next, this ripple voltage is determined as follows.
IOUT vs t1 (time) from when M1 is turned OFF (after tON) to when VOUT reaches the maximum level:
IOUT
=
IPK
−


VOUT
+ VD
L
−
VIN


•
t1
………………………………………………….………………...…(8)
∴
t1
=
(IPK
−
) IOUT
•


VOUT
+
L
VD
−
VIN


……………………………………………………………...…...(9)
When M1 is turned ON (after tOFF), IL = 0 (when the energy of the inductor is completely transmitted):
Based on equation (7),


VOUT
L
+ VD
−
VIN


=
tOFF
IPK
…………………………………………………………………..………….(10)
When substituting equation (10) for equation (9):
t1
=
tOFF
−


IOUT
IPK


•
tOFF
…………………………………………………………………………………(11)
Electrical charge ΔQ1 which is charged in CL during t1:
ΔQ1
=

t1
0
ILdt
=
IPK
•

t1
0
dt
−
VOUT
+ VD
L
−
VIN
•

t1
0
tdt
=
IPK
•
t1 −
VOUT
+ VD
L
−
VIN
•
1
2
t12
……….…...(12)
When substituting equation (12) for equation (9):
ΔQ1
=
IPK
−
1
2
(IPK
) − IOUT •
t1
=
IPK
+ IOUT
2
•
t1
…………………………………………………….…….(13)
A rise voltage (Vp-p) due to ΔQ1:
Vp
−
p
=
ΔQ1
CL
=
1
CL
•  ^IPK

+ IOUT
2
 • t1…………………………………………………………..……………(14)

When taking into consideration IOUT consumed during t1 and ESR^*1 (RESR) of CL:
Vp
−
p
=
ΔQ1
CL
=
1
CL
•  ^IPK

+ IOUT
2
 •

t1 +  ^IPK

+ IOUT
2
 • RESR

−
IOUT •
CL
t1
…………….………………….(15)
*1. Equivalent Series Resistance
15