
IDTP95020
Product Datasheet
September 2, 2011 Revision 1.3 Final
108
2011 Integrated Device Technology, Inc.
Table 168 – Register 0xA089 (0x89) Peak Current Limit (I_LIM) Settings Bits [3:2]
BIT 3 BIT 2 DESCRIPTION
0
Peak Current Limit = 25 %
0
1
Peak Current Limit = 50 %
1
0
Peak Current Limit = 75 %
1
Peak Current Limit = 100 % A
Note: Peak Current Limit is maximum when bits [3:2] are both set to 1.
Boost5 – Enable / Disable
There are two methods of disabling the BOOST5 Converter: the Global Enable bit and the local ENABLE bit. Table 169
shows the interoperation of the two methods.
Table 169. Interoperability of Enabling / Disabling Methods vs. Loading Default Values
INTERNAL
POR
GLOBAL
ENABLE
ON/OFF
STATUS
REGISTER VALUE STATUS
0
X
0
OFF
PREVIOUS SETTINGS
0
X
OFF
PREVIOUS SETTINGS
0
1
ON
PREVIOUS SETTINGS
1
X
OFF
LOAD DEFAULT VALUES
Initialization and Device Power-up
During an IC re-initialization or “cold boot”, an internal
POR disables the BOOST5 Converter and loads the
default values into the registers. The default values are
only loaded into the registers when there is a POR event.
The default settings for the Output Voltage Register are:
Table 170. Boost5 Output Voltage Register Default
FUNCTION
DEFAULT SETTING
Local Enable Bit
Disabled
Output Voltage
5.0V
Table 171. Boost5 Control Register Default
FUNCTION
DEFAULT SETTING
Current Limit
100%
Clock Frequency
1 MHz
After the POR releases, the Global Enable bit can be set
to HIGH. Since the default value of the local ENABLE bit
is LOW, the supply will not start at this time.
To enable the BOOST5 converter, the local ENABLE bit is
set to HIGH by writing a “1” to the Output Voltage Register.
The Output Voltage value must be included each time the
converter is enabled or disabled. The default value for the
converter is read and written back along with the ENABLE
bit or a different voltage can be written. When the
ENABLE bit becomes set the BOOST5 Converter enters
its soft-start sequence, ending up at the programmed
voltage.
NOTE: Changes to the Output Voltage Register settings
can be written directly without disabling the converter.
Normal Disabling / Enabling
Setting either the Global Enable bit to LOW or the local
ENABLE bit to LOW will turn off the BOOST5 Converter.
The Global Enable bit’s sole purpose is to shut down the
converter into its lowest power shutdown mode. It is not
intended to be used to toggle the BOOST5 Converter off
and on. Proper operation is only guaranteed by toggling
the ENABLE bit HIGH once the Global Enable bit is set
HIGH to take it out of low power shutdown mode.
Startup and Soft-Start
There is a direct path from VIN through the external
inductor (L) into the BOOST5_SWn pins, through SR1 to
the BOOST5_OUT pin which directly charges the output
capacitor (COUT) to ~VIN. During startup the converter
continues charging to the programmed Output Voltage
using Soft-Start. During the Soft Start sequence the
BOOST5 limits the peak inductor current for the first
500s.