RT1741A
Application Information
Power Good
The RT1741ABuck-BoostDC-DC converter can operate
with wide input voltage such as battery which is higher or
lower than the output voltage and it can supply the load
current up to 4A. The maximum peak current in the
switches is limited to a typical value of 4.5A. The typical
operating input voltage is between 1.8V and 5.5V. The
RT1741A output voltage can be set from 1.8V to 5.5V by
changing the external divider resistor on the FB pin for
the adjustable. The converter feedback loop is internally
compensated for both Buck and Boost operation and it
provides seamless transition between Buck and Boost
modes operation.
The RT1741A has a built-in power good function on
PGOOD pin to indicate whether the output voltage is
regulated properly or not. The PGOOD pin output is open-
drain, so the logic function can be adjusted to any voltage
level by connecting a pull-up resistor to the supply voltage.
When the output voltage is regulated properly, the PGOOD
pin becomes high impedance and indicates high level to
the power good output. When the output voltage is
regulated improperly, the PGOOD pin becomes low
impedance and indicates low level to the power good
output.
Enable
Power-Save Mode and Synchronization
The device can be enabled or disenabled by the EN pin.
When the EN pin is higher than the threshold of logic
high, the device starts operation with soft-start. Once the
EN pin is set at low, the device will be shut down. In
shutdown mode, the converter stops switching, internal
control circuitry is turned off, and the load is disconnected
from the input. This also means that the output voltage
can drop below the input voltage during shutdown.
The PS/SYNC pin can be used to select different operation
modes. When PS/SYNC is set low and the average
inductor current gets lower then about 400mA, Power Save
Mode can be enabled and used to improve efficiency.
At this point the converter operates with reduced switching
frequency and with a minimum quiescent current to
maintain high efficiency. When the load increases above
the minimum forced inductor current of about 400mA, the
device will automatically switch to PWM mode. The Power
Save Mode can be disabled by programming the PS/SYNC
high. Connecting a clock signal at PS/SYNC can force
the RT1741A switching frequency to synchronize to the
connected clock frequency. The PS/SYNC input supports
standard logic thresholds and the frequency range is
between 2.2MHz to 2.6MHz.
Output Voltage Setting
The RT1741Aoutput voltage can be set from 1.8V to 5.5V
by changing the external divider resistor on the FB pin.
When the adjustable output voltage version is used, the
resistor divider must be connected between VOUT, FB
andGND. The typical value of the voltage at the FB pin is
500mV and the RT1741A output voltage can be set from
1.8V to 5.5V. It is recommended to keep the resistor R2
value in the range of 200kΩ. From that, the value of the
resistor connected between VOUT and FB, R1, depending
on the needed output voltage, can be calculated as
following equation :
Dynamic Current Limit
To protect the device and the application, the peak inductor
current is limited internally on the IC.At nominal operating
conditions, this current limit is constant. The current limit
value can be found in the electrical characteristics table.
If the supply voltage at VINdrops below 2.3V, the current
limit is reduced. This can happen when the input power
source becomes weak. Increasing output impedance, when
the batteries are almost discharged, or an additional heavy
V
VFB
OUT
R1 = R2
1
Copyright 2019 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS1741A-01 January 2019
www.richtek.com
11
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