ACT81460
Rev 1.0, 18-Dec-2018
well as after responding to a short-circuit or other fault
condition and during retry after a fault.
BUCK-BOOST REGULATOR
General Description
Output Voltage Setting
ACT81460 contains a fully integrated, four-switch,
buck-boost regulator. It operates from an input voltage
range of 2.7V to 5.5V and provides an output range be-
tween 3.2V and 5.0V.
Output voltage for the buck-boost regulator can be pro-
grammed in 50mV steps from 3.20V to 5.0V. The buck-
boost regulates to the voltage defined by I2C register
VSET0. It can be programmed between 3.2V and 5.0V
in 50mV steps. The following equation calculates the
output voltage based on the VSET0 register setting.
The four integrated MOSFETS minimize the cost and
size of the solution with minimal external components
needed for the buck-boost function. The buck-boost can
be configured via I2C to operate in Buck Only mode,
Boost Only mode, or Buck-Boost mode. These bits are
not user accessible. Refer to the CMI Options section
for each CMI’s specific setting.
Vbuck-boost = 3.2V + VSET0 * 0.05V
Where VSET0 is the decimal equivalent of the value in
the I2C VSET0 register. The VSET0 register contains an
unsigned 6-bit binary value. As an example, if the
VSET0 register contains 100100b (36decimal), the out-
put voltage is 5.0V.
In CCM mode, there are four user-selectable frequen-
cies between 1.5MHz and 3.3MHz. The buck-boost is
available with a variety of standard and custom output
voltages and may be software-controlled via the I2C in-
terface for systems that require advanced power man-
agement functions.
Changes to the output voltage are intended to be per-
formed with CMI settings. The output voltage should not
be changed in final production. For development and
experimentation, the output voltage may be changed by
+-20% from the default setting. Voltage changes larger
than +/- 20% require different factory trim settings (new
CMI). Programming the output voltage farther than 20%
from the default setting may damage the IC.
Operating Mode
The buck-boost regulator emulates operation of a fixed-
frequency regulator at medium to heavy loads. It transi-
tions to a proprietary power-saving mode at light loads
to save power and improve efficiency. The buck-boost
is optimized to reduce its input current during off/shut-
down and standby modes when there is no load current
and the regulator is left on with the output regulating.
The output voltage can be configured via I2C.
Table 6 shows the output voltage as a function of the
VSET0 register setting. Do not program the VSET0 reg-
isters to a value greater than 100100b. Programming
higher than this may damage the IC.
Buck-Boost Output Voltage (V)
VSET0 [5:3]
Synchronous Rectification
The buck-boost features an integrated full H-bridge with
two high side (HS) and two low side (LS) power
MOSFETs. The LS MOSFETS are used in a fully syn-
chronous mode to maximize efficiency and minimize the
total solution size and cost by eliminating the need for
external rectifiers.
000
001
010
011
100
101
110
111
000
001
010
011
100
101
110
111
3.20
3.25
3.30
3.35
3.40
3.45
3.50
3.55
3.60
3.65
3.70
3.75
3.80
3.85
3.90
3.95
4.00
4.05
4.10
4.15
4.20
4.25
4.30
4.35
4.40
4.45
4.50
4.55
4.60
4.65
4.70
4.75
4.80
4.85
4.90
4.95
5.00
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Note that an additional Schottky diode is required when
the output voltage is greater than 4.7V. Connect the an-
ode to SWBB2 and the cathode to VBBST. The diode
should be placed on the top layer with direct connec-
tions to these two pins. Refer to the EVK for layout de-
tails.
N/A
N/A
Table 6. Vout vs VSET0 Register Setting
Soft-Start
DVS
The buck-boost regulator includes an internal 800µs
soft-start ramp which limits the rate of change of the out-
put voltage, minimizing input inrush current and ensur-
ing that the output powers up in a monotonic manner
that is independent of loading on the outputs. This cir-
cuitry is effective any time the regulator is enabled, as
The buck-boost does not have DVS functionality.
Enable / Disable Control
During normal operation, the buck-boost may be ena-
bled or disabled via the I2C interface by writing to its ON
bit. Note that disabling the buck-boost if it is used as an
Innovative PowerTM
ActiveSwitcherTM is a trademark of Active-Semi
www.active-semi.com
Copyright © 2018 Active-Semi, Inc.
41
ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
