SMALL PACKAGE PWM/PFM CONTROL STEP-UP SWITCHING REGULATOR
Rev. 7.2-10
S-8324/8328 Series
Seiko Instruments Inc.
15
Test Circuits
Operation
1. Step-Up DC/DC Converter
The S-8324/8328 series is a DC/DC converter using a pulse frequency modulation method (PFM) or a pulse width modulation
method (PWM) which are switched automatically according to the load current with a low current consumption.
Especially in the region of 100
A output load current, a high-efficiency DC/DC converter is obtained.
In conventional fixed-duty type PFM DC/DC converters, pulses are skipped at low output load current, causing fluctuation in ripple
frequency of the output voltage, with the result of increase in ripple voltage.
The S-8324/8328 series operates with the PWM control which changes the pulse width duty from 15% to 83%(78% for H, J types)
in the region of large output load current.
The ripple voltage generated from switching can be removed easily through the filter because the switching frequency is constant.
The S-8324/8328 series operates with the PFM control which skips the pulse of the duty 15% pulth width and output that pulse to
the switching transistor according to the load current.
From the above operation, the self current consumption is reduced from the blocking oscilation of the oscilation circuit, and a fall
of efficiency can be protected in small load.
The switching point between PWM and PFM control differs according to the external elements (coil, diode and other), input
voltage and output voltage.
See reference data about this.
Shutdown pin: Stops or starts step-up operation.
(Only for SOT-23-5 package products of A, B, and H Series.)
Turning the shutdown pin low stops operation of all the internal circuits and reduces current consumption
significantly. Do NOT use the shutdown pin in floating state because it has a structure shown in Figure 4 and is
not pulled up or pulled down internally. Do NOT apply voltage of between 0.3 V and 0.75 V to the shutdown pin
because applying such voltage increases the current consumption. If the shutdown pin is not used, connect it to
VOUT (VDD for D, E, J types) pin.
The shutdown pin doesn’t have hysteresis.
Shutdown pin
CR oscillation
circuit
Output
voltage
“H”
Operation
Fixed
“L”
Stop
VIN*
* Voltage obtained by extracting the voltage drop due
to DC resistance of the inductor and the diode
forward voltage from VIN.
1.
VSS
VOUT
CONT
V
-
+
-
+
(ON/OFF)
(VDD)
3.
VSS
VOUT
V
-
+
-
+
(ON/OFF)
Rb
EXT
Cb
(VDD)
Figure 3
Oscilloscope
2.
VSS
(ON/OFF)
VOU
CONT
10 k
-
+
A
(VDD)
4.
Oscilloscope
VSS
(ON/OFF)
VOUT
-
+
A
EXT
(VDD)
ON/OFF
VOUT
(VDD for D, E, J types)
VSS
Figure 4
DISCONTINUED
PRODUCT