S-8533A15AFT-TB-G Seiko Instruments, S-8533A15AFT-TB-G Datasheet - Page 10

• Manufacturer Part Number: S-8533A15AFT-TB-G
• Description: IC CTRL PWM SYNC SD 1.5V 8-TSSOP
• Manufacturer: Seiko Instruments
• Type: Step-Down (Buck)r

Specifications of S-8533A15AFT-TB-G

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.5V
• Frequency - Switching: 300kHz
• Voltage - Input: 2.7 ~ 16 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-TSSOP
• Power - Output: 300mW
• Output Voltage: + 1.3 V to + 6 V
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

10
STEP-DOWN, SYNCHRONOUS PWM CONTROL SWITCHING REGULATOR CONTROLLER
S-8533 Series
3. ON/OFF Pin (Shutdown Pin)
4. 100% Duty Cycle
5. Back-Flow Current
This pin is used to activate and deactivate the step-down operation.
When the ON/OFF pin is set to “L”, all the internal circuits stop working, and substantial savings in current
consumption are thus achieved. The voltage of the PDRV pin goes to V
to V
The ON/OFF pin is configured as shown in Figure 8. Since pull-up or pull-down is not performed internally,
operation where the ON/OFF pin is in a floating state should be avoided. Application of a voltage of 0.3 to 1.8 V to
the pin should also be avoided lest the current consumption increases. When the ON/OFF pin is not used, it should
be connected to the VIN pin.
The S-8533 Series operates with a maximum duty cycle of 100%. The switching transistor can be kept on to supply
current to the load continually, even in cases where the input voltage falls below the preset output voltage value.
The output voltage under these circumstances is equal to the subtraction of the lowering due to the DC resistance
of the coil and the on-resistance of the switching transistor from the input voltage.
Since the S-8533 Series performs PWM synchronous rectification under a light load, current flows backward in the
V
to the maximum back-flow current value, which can be calculated from the following expressions.
When there is no load, the current waveform becomes a triangular wave with the maximum, I
minimum, I
When the output current (I
backward since the minimum value (I
When an input capacitor (C
current is absorbed by the input capacitor. The input capacitor is indispensable to reduce back-flow current to the
power source.
IN
Duty (I
ΔI
I
direction. The back-flow current therefore reaches its peak when there is no load (see Figure 9). Pay attention
L
SS
Figure 8 ON/OFF Pin Structure
max. = ΔI
L
ON/OFF
= ΔV/L × ton = (V
level to shut off the respective transistors.
OUT
L
min., which is negative. The negative current, shaded regions in Figure 10, flows backward.
= 0) = V
L
/2 = 109 mA, I
OUT
IN
/V
− V
IN
OUT
IN
L
OUT
) is installed, back-flow current to the power source is negligible since the back-flow
V
min. = −ΔI
Example : V
Example : V
) is approximately 109 mA under the above conditions, the current does not flow
IN
V
) × Duty/(L × f
SS
L
min) of the triangular wave becomes 0 mA.
L
/2 = −109 mA
Seiko Instruments Inc.
IN
IN
= 5 V, V
= 5 V, V
OSC
) × 1.2
OUT
OUT
ON/OFF Pin
= 3 V, Duty = 60%
= 3 V, f
“H”
“L”
OSC
= 300 kHz, L = 22 μH, ΔI
CR Oscillation
IN
Non-active
level and voltage of the NDRV pin goes
Circuit
Active
Set value
L
Voltage
Output
= 218 mA
Open
L
Rev.3.0
max., and the
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