S-8363B-I6T1U2 Datasheet, PDF (9/50 Pages) Seiko Instruments Inc – PWM/PFM SWITCHABLE SWITCHING REGULATOR

STEP-UP, SUPER-SMALL PACKAGE, 1.2 MHz PWM/PFM SWITCHABLE SWITCHING REGULATOR
Rev.2.0_01
S-8363 Series
2. Low voltage start-up
2. 1 Start-up circuit
The S-8363 Series can startup from 0.9 V. When the VOUT voltage at ON / OFF = “H” does not reach the STU
release voltage, the start-up circuit starts the operation and outputs the fixed duty pulse to the CONT pin. By
this, the VOUT voltage starts step-up. After that, the VOUT voltage reaches the STU release voltage and the STU
mode circuit is set in STU release condition, therefore, the switching control circuit starts stable operation due
to the soft-start function. Simultaneously, the start-up circuit is set in disable condition, so that the S-8363
Series prevents excessive current consumption.
2. 2 Start-up mode (STU mode) circuit
The STU mode circuit monitors the VOUT voltage, and switches the operation modes between start-up period
and normal control period of the switching control circuit. The STU release voltage is internally fixed at 1.4 V
(typ.), and has hysteresis of approx. 0.15 V. When the VOUT voltage decreases to 1.25 V (typ.) from release
condition, the STU mode circuit is set in the STU detection condition, shifting to the start-up period. Several μs
to several ten μs is taken to shift from STU release to PWM release. During this the step-up operation is not
performed, therefore, the VOUT voltage may largely decrease depending on the size of load.
During applying ON / OFF = “L”, the STU mode circuit is set in disable condition, so that the S-8363 Series
prevents excessive current consumption.
L = 2.2 μH
SD
VOUT
STU Mode Circuit
CONT
V_D
Switching
Control Circuit
VIN
MUX
VIN
Start-up
Circuit
VSS
C_OUT
10 μF
Figure 8 Start-up Circuit
VOUT
Load
Output voltage
(V_OUT)
STU release
STU detection
Switching delay
CONT voltage
(V_CONT)
Start-up period
PWM control period
Figure 9 Start-up Sequence
Time [s]
9