
P95020 / Preliminary Datasheet
Revision 0.7.10
86
2010 Integrated Device Technology, Inc.
9.3.2
LED_BOOST - Control Register
This Register contains clock select settings
IC Address = Page-0: 135(0x87), C Address = 0xA087
Bit
Bit Name
Def.
Set.
User
Type
Value
Description / Comments
0
RESERVED
0b
RW
RESERVED
1
LED_BOOST_CLK_SEL
1b
RW
1 = 1.0 MHz
0 = 0.5 MHz
Clock Frequency
[3:2]
RESERVED
00b
RW
RESERVED
[5:4]
RESERVED
N/A
R
RESERVED
[7:6]
RESERVED
00b
RW
RESERVED
9.4
LED_BOOST - ENABLING & DISABLING
There are two methods of disabling the LED_BOOST Converter: the Global Enable bit and the local ENABLE bit (Output
Current Register, Bit 7).
Table 23 shows the interoperation of the two methods.
Table 23
– Interoperability of enabling/disabling methods vs. loading default values.
Internal POR
Global Enable
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
9.4.1
LED_BOOST - Initialization and Power-Up
During an IC re-
initialization or “cold boot” an internal POR disables the LED_BOOST 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 Current Register are:
Function
Default Setting
Local Enable Bit
Disabled
Scale
High
Output Current
0.78 mA
The default settings for the Control Register are:
Function
Default Setting
Clock Frequency
1 MHz
After the internal POR releases, the Global Enable bit can be set to HIGH. Since the default value of the local ENABLE
bit is LOW, the converter will not start at this time.
To enable the converter, the local ENABLE bit is set to HIGH by writing a “1” to the Output Current Register. The Output
Current value must be included each time the converter is enabled or disabled. The default value for the converter can be
read and written back along with the ENABLE bit or a different value can be written. When the ENABLE bit is set, the
LED_BOOST Converter will begin its soft-start sequence, ending at the programmed current.
NOTE: Changes to the Output Current Register settings can be written directly without disabling the converter.
9.4.2
LED_BOOST - Normal Disabling / Enabling
Setting either the Global Enable bit to LOW or the local ENABLE bit to LOW will turn off the LED_BOOST Converter.
The Global Enable
bits sole purpose is to shut down the converter into its lowest power shutdown mode. It is not
intended to be used to toggle the LED_BOOST 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.
9.4.3
LED_BOOST - SOFT START
The LED BOOST uses the combination of a reduced initial current limit setting with the slow charge of its large internal
compensation capacitor to affect a controlled ramp of the output supply. This limits the inrush current and consequently
helps eliminate drooping in the input supply during the ramp up