R1221N Datasheet, PDF (7/21 Pages) RICOH electronics devices division – Step-down DC/DC Converter with Voltage Detector

n TYPICAL APPLICATIONS AND APPLICATION HINTS
PMOS
L
EXT
VIN
VOUT
Vcc
R1
CIN
CE
SD1
COUT
GND
VDOUT
Reset/
CE CONTROL
PMOS: HAT1020R (Hitachi), Si3443DV (Siliconix)
SD1 : RB491D (Rohm)
CIN :10mF(Tantalum Type)
CPU
L : CD105(Sumida, 27mH)
COUT : 47mF(Tantalum Type)
R1 : 100kW
When you use these ICs, consider the following issues;
l As shown in the block diagram, a parasitic diode is formed in each terminal, each of these diodes is not formed
for load current, therefore do not use it in such a way. When you control the CE pin by another power supply,
do not make its "H" level more than the voltage level of VIN pin.
l Detector threshold hysteresis is set at 3 percent of detector threshold voltage. (Min. 1 percent, Max. 5 percent)
l Setting Detector threshold voltage range depends on Output voltage of DC/DC converter.
Release Voltage from Reset condition must not be more than Output voltage of DC/DC converter.
(Detector Threshold Voltage´1.07 < Output Voltage of DC/DC converter´0.98
l When the R1221NXXXX is on stand-by mode, the output voltage of VDOUT is GND level, therefore if the pull-up
resistor for VDOUT pin is pulled up another power supply, a certain amount of current is loading through the
resistor.
l The operation of Latch-type protection circuit is as follows;
When the maximum duty cycle continues longer than the delay time for protection circuit, (Refer to the Electrical
Characteristics) the protection circuit works to shut-down the external Power MOS with its latching operation.
Therefore when an input/output voltage difference is small, the protection circuit may work even at small load
current.
To release the protection state, after disable this IC with a chip enable circuit, enable it again, or restart this IC
with power-on. However, in the case of restarting this IC with power-on, after the power supply is turned off, if
a certain amount of charge remains in CIN, or some voltage is forced to VIN from CIN, this IC might not be
restarted even after power-on.
If rising transition speed of supply voltage is too slow, or the time which is required for VIN voltage to reach
Output Voltage of DC/DC converter is longer than soft-starting time plus delay time for protection circuit,
protection circuit works before VIN voltage reaches Output Voltage of DC/DC converter. To avoid this condition,
make this IC disable(CE=”L”) first, then force VIN voltage, and after VIN voltage becomes equal or more than
VOUT, make this IC enable(CE=“H”).
l Set external components as close as possible to the IC and minimize the connection between the components
and the IC. In particular, a capacitor should be connected to VOUT pin with the minimum connection. And make
sufficient grounding and reinforce supplying. A large switching current flows through the connection of power
supply, an inductor and the connection of VOUT. If the impedance of power supply line is high, the voltage level of
power supply of the IC fluctuates with the switching current. This may cause unstable operation of the IC.
Rev. 1.11
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