RT6154A/B
pulse load is connected to the battery can cause the VIN
voltage to drop. The dynamic current limit has its lowest
value when reaching the minimum recommended supply
voltage at VIN.
Inductor Selection
To properly configure the Buck-Boost converter, an
inductor must be connected between the LX1 and LX2
pins. To estimate the inductance value, two equations are
listed as below :
Soft-Start and Short Circuit Protection
V
OUT
V
V
IN(MAX) OUT
L1 >
(H)
After being enabled, the device starts operating. The
current limit ramps up from an initial 1Afollowing the output
voltage increasing. At an output voltage of about 1.2V, the
current limit is at its nominal value. If the output voltage
does not increase, the current limit will not increase. There
is no timer implemented. Thus, the output voltage
overshoot at startup, as well as the inrush current, is kept
at a minimum. The device ramps up the output voltage in
a controlled manner even if a large capacitor is connected
at the output. When the output voltage does not increase
above 1.2V, the device assumes a short circuit at the
output, and keeps the current limit low to protect itself
and the application. At a short on the output during
operation, the current limit also is decreased accordingly.
f I V
L
IN(MAX)
V
V
V
IN(MIN)
IN(MIN)
OUT
L2 >
(H)
f I V
L
OUT
where f is the minimum switching frequency. L1 is the
minimum inductor value for Buck mode operation. VIN(MAX)
is the maximum input voltage. L2 is the minimum
inductance for Boost mode operation. VIN(MIN) is the
minimum input voltage. The recommended minimum
inductor value is either L1 or L2 whichever is higher. For
example, a suitable inductor value is 2.2μH for generating
a 3.3V output voltage from a Li-Ion battery with the range
from 2.5V to 4.2V. The recommended inductor value range
is between 1.5μH and 4.7μH. In general, a higher inductor
value offers better performance in high voltage conversion
condition.
Protection
Table 1. Inductor Suggestion
Additional protections of the RT6154A/B include current
overload protection, output over-voltage clamp, and thermal
shutdown. To protect the device from overheating, the
device has a built-in temperature sensor which monitors
the internal junction temperature. If the temperature
exceeds a threshold, the device stops operating. As soon
as the IC temperature decreases below the threshold with
a hysteresis, it starts operating again. The built-in
hysteresis is designed to avoid unstable operation at IC
temperatures near the over-temperature threshold.
Vendor
Inductor Series
Taiyo Yuden
NRS5024T2R2NMGJ
Output Capacitor Selection
The output capacitor selection determines the output
voltage ripple and transient response. It is recommended
to use ceramic capacitors placed as close as possible to
the VOUT and GND pins of the IC. If, for any reason, the
application requires the use of large capacitors which can
not be placed close to the IC, using a small ceramic
capacitor in parallel to the large one is recommended.
This small capacitor should be placed as close as possible
to the VOUT and GND pins of the IC. The output voltage
ripple for a given output capacitor is expressed as follows :
Under-Voltage Lockout
The under-voltage lockout circuit prevents the device from
operating incorrectly at low input voltages. It prevents the
converter from turning on the power switches under
undefined conditions and prevents the battery from deep
discharge. PVIN voltage must be greater than 1.7V to
enable the converter. During operation, if PVIN voltage
drops below 1.6V, the converter is disabled until the supply
exceeds the UVLO rising threshold. The RT6154A/B
automatically restarts if the input voltage recovers to the
input voltage UVLO high level.
VOUT (VIN VOUT
)
VOUT, peak (Buck) =
VOUT, peak (Boost) =
V
IN 8L(fOSC )2 COUT
ILOAD (VOUT V )
IN
COUT VOUT fOSC
Copyright 2017 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
12
DS6154A/B-03 May 2017
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
