RT2701
Operation
The RT2701 integrates a PWM controller, two 12V
MOSFET drivers with internal bootstrap diodes, as well
as output current monitoring and protection functions.
Power On Reset
The Power On Reset (POR) circuit monitors the supply
voltage of the controller (VCC). When VCC exceeds the
POR rising threshold, the controller will be enabled. If
VCC falls below the POR falling threshold during normal
operation, all MOSFETs stop switching. There is a
hysteresis between the POR rising threshold and falling
threshold to prevent noise mis-trigger.
Soft-Start
An internal soft-start function is used to prevent large
inrush current while converter is powered-up. The FB
voltage will track the internal soft-start voltage during soft-
start interval. During the soft-start period, the controller
will operate in dual-phase mode to ensure enough charge
for output loads.
EN/Mode Select
The RT2701 supports DEM (Diode Emulation Mode) and
ASM (Audio Skipping Mode) operation which can be
enabled by EN/MSEL pin. When the EN/MSEL pin is
pulled up above 4.2V, the controller will operate in DEM
and reduce the switching frequency at light load conditions
for saving power loss. If the EN/MSEL voltage is between
1.2V and 3V, the controller will operate in ASM. In ASM
operation, the minimum switching frequency is limited to
30kHz to avoid acoustic noises. If the pin is pulled to
GND, the RT2701 will be shut down.
Current Balance
The RT2701 implements internal current balance
mechanism in the current loop. The RT2701 senses each
phase current signal and compares it with the average
current. If the sensed current of any particular phase is
higher than average current, the on-time of this phase will
be adjusted to be shorter.
OCP
Once the sensed total current exceeds the current limit
threshold, the driver will be forced to turn off the gate drivers
for high side power MOSFETs. Until the OCP situation is
removed.
Over Voltage Protection
The RT2701 monitors the output voltage via the CSN pin
for Over Voltage Protection (OVP). Once the output voltage
exceeds the OVP threshold, the controller will turn off
high side MOSFETs and turn on low side MOSFETs to
protect the load until the OVP situation is removed.
Under Voltage Protection
The voltage on CSN pin is also monitored for Under Voltage
Protection (UVP). If the output voltage is lower than the
UVP threshold, the controller will turn off both high side
and low side MOSFETs. When the UVP is triggered, the
RT2701 will enter hiccup mode and continuously try to
restart until the UVP situation is removed.
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS2701-00 May 2013
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
