RV5VH Datasheet, PDF (19/47 Pages) RICOH electronics devices division – DC/DC CONVERTER CONTROLLER

RV5VH1××/RV5VH2××
OPERATION
• DC/DC Converter 1
RV5VH1××
Vref
OSC
p_shift
Error Amp.1
VLX lim.
VFM1
VOUT1
3
R
LX1
4
SBD
C
L
VIN
VOUT1
RV5VH2××
Vref
OSC
p_shift
Error Amp.1
VFM1
VOUT1
3
R
SBD
L1
C
EXT1 _Rb
4
NPN Tr.
Cb
VIN
VOUT1
The DC/DC1 uses input voltage as an initial power supply, once boost operation is started, the boost output will be used
for the power supply of device itself. A change in the VOUT1 will feed back to the internal error amplifier through external
voltage setting resistors and internal feed back resistors. When the feed back voltage is lower than the reference voltage
the error amplifier enables oscllation or otherwise will stop oscillation. The internal feed back resistor “R” which is fixed
and adjusted by laser trim can make the feed back input voltage to “Error Amp.1” stable. Pulses from the “OSC” circuit
have a duty cycle of 50% and it becomes 65 to 75%(at high side) through the “P_shift” circuit. The duty cycle may be
smaller with light load spontaneously.
These clook pulses control VFM circuit and make it possible to operate as a boost converter. The output of LX1 is Nch open
drain, while the output of “EXT1” is driven by CMOS buffer and an external NMOS driver is also available instead of an
NPN transistor, in such cases the Rb and the Cb are not necessary. A recommended Rb is 300Ω. When you use a MOS-
FET for the EXT1, the input voltage should be high enough and you can get high effiiciency applications.
A current limit is available only for the RV5VH1 series, to prevent an excess current from flowing through Nch driver tran-
sistor.
The DC/DC1 can be shut down by CSW pin. When the CSW pin is High, VDD level, the DC/DC1 is enabled and when the
CSW pin is “L”, GND level, the DC/DC1 is disabled. The EXT1 pin outputs “L” while the DC/DC1 is disabled.
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