S-882Z Seiko Instruments, S-882Z Datasheet - Page 10

• Manufacturer Part Number: S-882Z
• Description: ULTRA-LOW VOLTAGE OPERATION CHARGE PUMP IC
• Manufacturer: Seiko Instruments

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10
ULTRA-LOW VOLTAGE OPERATION CHARGE PUMP IC FOR STEP-UP DC-DC CONVERTER STARTUP
S-882Z Series
Selection of Product and Startup Capacitor (C
V
C
To reliably start up the step-up DC-DC converter, in the S-882Z Series, select the discharge start voltage value
(V
converter to be started, its external parts, and the output load.
Generally, an output smoothing capacitor with a large capacitance value and an output load are connected to the
output pin of the step-up DC-DC converter. Therefore, to start up the step-up DC-DC converter thus connected, it
is necessary to select a large capacitance value for the startup capacitor.
As a reference, the following shows an example that a Schottky diode (SD1) is added between the output pin
(OUT) and the power supply pin (VDD) of the step-up DC-DC converter to be started up in the S-882Z Series
(refer to Figure 14 ). As a result, it is possible to start up the step-up DC-DC converter by the capacitor with a
small value.
C
The selection method for V
performed is described below.
Select V
CPOUT1
CPOUT
VDD
V
CPOUT1
C
V
C
C
I
V
t
CPOUT1
VDD
S
CPOUT
CPOUT1
DDL
CPOUT
VDD
:
in Figure 14 is the power supply smoothing capacitor of the step-up DC-DC converter.
V
C
> 10C
:
> V
:
) and the capacitance value of the external startup capacitor (C
IN
CPOUT1
:
IN
• C
+ C
: Capacitance value of startup capacitor (unit : µF)
DDL
: Discharge start voltage value of S-882Z Series (unit : V)
Capacitance value of power smoothing capacitor for step-up DC-DC converter (unit : µF)
Consumption current value of step-up DC-DC converter (unit : mA)
Minimum operation voltage of step-up DC-DC converter (unit : V)
Step-up DC-DC converter startup time ≅ Soft start time (unit : ms)
CPOUT
VDD
VDD
+ 0.2 V
VIN
and C
− 0.1 • I
CPOUT
CPOUT
S-882Z Series
VSS
so that they satisfy the following conditional expression.
VDD
CPOUT1
− V
Figure 14 Connection Diagram (Reference)
DDL
C
and C
CPOUT
OUT
VM
Seiko Instruments Inc.
• (C
CPOUT
CPOUT
when the reference connection shown in Figure 14 has been
+ C
VIN
VDD
) > 2t
C
CPOUT
Step-up DC-DC converter
VDD
S
• I
VSS
)
VDD
VDD
CPOUT
) according to the step-up DC-DC
SD1
OUT
Rev.1.2
C
V
L
OUT
_00
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