RT8004PCP

Manufacturer Part NumberRT8004PCP
ManufacturerRichtek Technology Corporation
RT8004PCP datasheet
 
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Function Block Diagram

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RT8004

Function Block Diagram

SYNC
ExtSyn
COMP
0.8V
EA
FB
EN/SS
Ext_SS
SD
Int_SS
POR
VDD
GND
Operation
Main Control Loop
The RT8004 is a monolithic, constant-frequency, current mode step-down DC/DC converter. During normal operation,
the internal top power switch (P-Channel MOSFET) is turned on at the beginning of each clock cycle. Current in the
inductor increases until the peak inductor current reach the value defined by the voltage on the COMP pin. The error
amplifier adjusts the voltage on the COMP pin by comparing the feedback signal from a resistor divider on the FB pin
with an internal 0.8V reference. When the load current increases, it causes a reduction in the feedback voltage relative
to the reference. The error amplifier raises the COMP voltage until the average inductor current matches the new load
current. When the top power MOSFET shuts off, the synchronous power switch (N-Channel MOSFET) turns on until
either the bottom current limit is reached or the beginning of the next clock cycle. The bottom current limit is set at −2A.
The operating frequency is set by an external resistor connected between the RT pin and ground. The practical switching
frequency can range from 300kHz to 4MHz.
Power Good comparators will pull the PGOOD output low if the output voltage comes out of regulation by 12.5%. In an
overvoltage condition, the top power MOSFET is turned off and the bottom power MOSFET is switched on until either
the overvoltage condition clears or the bottom MOSFET’ s current limit is reached.
Frequency Synchronization
The internal oscillator of the RT8004 can be synchronized to an external clock connected to the SYNC pin. The
frequency of the external clock can be in the range of 300kHz to 4MHz. For this application, the oscillator timing resistor
should be chosen to correspond to a frequency that is about 20% lower than the synchronization frequency.
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RT
ISEN
Slope Com
Oscillator
Output
Limit
Clamp
0.9V
Control
Logic
0.7V
0.4V
0.8V
POR
BG
OTP
V
REF
PVDD
OC
LX
Driver
NISEN
PGND
NMOS I Limit
PGOOD
DS8004-03
September 2007