R1221N RICOH electronics devices division, R1221N Datasheet - Page 7

• Manufacturer Part Number: R1221N
• Description: Step-down DC/DC Converter with Voltage Detector
• Manufacturer: RICOH electronics devices division

n n n n TYPICAL APPLICATIONS AND APPLICATION HINTS
CE CONTROL
l As shown in the block diagram, a parasitic diode is formed in each terminal, each of these diodes is not formed
l
l
l
l The operation of Latch-type protection circuit is as follows;
l Set external components as close as possible to the IC and minimize the connection between the components
Rev. 1.11
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
resistor for VD
resistor.
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 C
restarted even after power-on.
Output Voltage of DC/DC converter is longer than soft-starting time plus delay time for protection circuit,
protection circuit works before V
make this IC disable(CE=”L”) first, then force V
V
When you use these ICs, consider the following issues;
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 V
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.
and the IC. In particular, a capacitor should be connected to V
sufficient grounding and reinforce supplying. A large switching current flows through the connection of power
supply, an inductor and the connection of V
power supply of the IC fluctuates with the switching current. This may cause unstable operation of the IC.
Detector threshold hysteresis is set at 3 percent of detector threshold voltage. (Min. 1 percent, Max. 5 percent)
Setting Detector threshold voltage range depends on Output voltage of DC/DC converter.
If rising transition speed of supply voltage is too slow, or the time which is required for V
OUT
When the R1221NXXXX is on stand-by mode, the output voltage of VD
To release the protection state, after disable this IC with a chip enable circuit, enable it again, or restart this IC
PMOS: HAT1020R (Hitachi), Si3443DV (Siliconix)
SD1 : RB491D (Rohm)
C
IN
, make this IC enable(CE=“H”).
C
IN
:10mF(Tantalum Type)
OUT
V
CE
pin is pulled up another power supply, a certain amount of current is loading through the
IN
PMOS
GND
EXT
IN
voltage reaches Output Voltage of DC/DC converter. To avoid this condition,
VD
V
OUT
OUT
IN
, or some voltage is forced to V
OUT.
IN
If the impedance of power supply line is high, the voltage level of
SD1
voltage, and after V
- 7 -
L
IN
C
pin.
OUT
R1 : 100kW
L : CD105(Sumida, 27mH)
C
OUT
OUT
: 47mF(Tantalum Type)
pin with the minimum connection. And make
IN
voltage becomes equal or more than
R1
OUT
IN
from C
is GND level, therefore if the pull-up
Vcc
Reset/
IN
, this IC might not be
CPU
IN
voltage to reach
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