RT6154A/B
Application Information
Power Good
The RT6154A/B Buck-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 5A at VIN = 3.6V
and 2.6Aat VIN = 2.1V. The typical operating input voltage
is between 1.8V and 5.5V. The RT6154A 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
RT6154B output voltage is fixed to 3.3V. 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 RT6154A/B 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.
Power-Save Mode and Synchronization
Enable
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.
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.
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 RT6154A/B 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 RT6154Aoutput voltage can be set from 1.8V to 5.5V
by changing the external divider resistor on the FB pin.
The RT6154B output voltage is fixed to 3.3V. 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 RT6154A 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 2017 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS6154A/B-03 May 2017
www.richtek.com
11
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
