RT5800
Operation
The RT5800 is a power management IC that integrates
four high efficiency Buck converters, and is factory
configured as a 2/1/1 phase converter. Each of the four
converters provides up to 5A output current over an
input supply voltage range of 3.3V to 6V.
The RT5800 utilizes the proprietary Advanced Constant
On-Time (ACOT
TM
) control architecture. The ultrafast
ACOT
TM
control enables the use of small ceramic
capacitors (MLCC) to save the PCB size.
During normal operation, the internal high-side power
switch (HSFET) is turned on for a fixed interval
determined by a one-shot timer at the beginning of each
clock cycle. When the HSFET is turned off, the internal
low-side power switch (LSFET) is turned on. The output
voltage is sensed remotely at VOUTx and RTNx for high
accuracy and is compared to an internal reference
voltage. Hence, the error signal is obtained and
internally compensated. The compensated error signal
is then compared to an internal ramp signal. When the
minimum off-time one-shot (100ns, max.) has timed out
and the inductor current is below the current limit
threshold, the one-shot is triggered again if the internal
ramp signal falls below the compensated error signal.
The ACOT
TM
control architecture features ultrafast
transient response. When a load is suddenly increased,
the output voltage drops quickly. and triggers a new
on-time to rise inductor current again.
Dynamic Voltage Scaling (DVS)
The RT5800 provides wide output voltage range with
8-bits resolution and each Buck converter has two
independently programmable voltage setting. They are
called DVS0 and DVS1. Take Buck1 as two-phase
configuration for an example, register 0x48[8:0] can set
voltage of DVS0 while 0x4A[8:0] is used to set voltage
of DVS1. There are two methods to select the DVS. For
the first method, it can be changed by software from
register 0x52[1:0]. Control DVS0 by setting
0x52[1:0]=00 and DVS1 by setting 0x52[1:0]=01. For
the second method, selecting the DVS can be from
external hardware pin when setting 0x52[1:0]=10.
VSELA pin can be this role and its polarity is defined by
0x52[2]. When setting 0x52[2]=0, pull VSELA high to
Copyright © 2019 Richtek Technology Corporation. All rights reserved.
let DVS0 be used and pull VSELA low to let DVS1 be
used. Conversely, when setting 0x52[2]=1, pull VSELA
high to let DVS1 be used and pull VSELA low to let
DVS0 be used.
The RT5800 also supports DVS speed configuration,
whether the slew rate of voltage changing in the same
DVSx or between DVS0 and DVS1. Take Buck1 as
two-phase configuration for an example, when output
voltage is set from low to high or high to low, register
0x54[6:4] defines slew rate of DVS up while 0x54[2:0]
is used to define slew rate of DVS down. In order to
have better performance during voltage changing
operation, the master/slave enters PWM operation and
keeps 200s after the voltage achieves target even
when IC is set to Auto mode. Figure 1 and Figure 2
show the DVS up and down operation.
95%
VOUT
Intial Voltage
Target Voltage
5%
Master
Switch
Slave
Switch
Command
DVS Up Slew Rate
Register Setting
200μs
Figure 1. DVS Up Operation
Intial Voltage
VOUT
5%
95%
Target Voltage
Master
Switch
Slave
Switch
Command
DVS Down Slew Rate
Register Setting
200μs
Figure 2. DVS Down Operatio
n
is a registered trademark of Richtek Technology Corporation.
DS5800-00
November 2019
www.richtek.com
5
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
