• 07/14/2017
  • Public Content
Contents

Boot Strap Signal Isolation

Intel has updated the design guide and datasheet for the Intel® Joule™ compute module.
For those designing a carrier board that interfaces with the Intel® Joule™ compute module, we want to make sure you’re aware that the compute module contains several signals that act as module “boot strap” signals, which are latched during the module boot process. These boot strap signals are listed in required strapping of module pins in the Intel® Joule™ module datasheet. In order to ensure that the module boots properly, the expansion board designer must isolate expansion board circuitry from the module’
s
boot strap signals during the boot process. Failure to provide proper isolation may result in the module failing to boot or module features disabled.
The Intel® Joule™ compute module provides a signal, PMIC_PWRGOOD, that can be used to determine when the boot process is complete and thus should be used to enable and disable the isolation circuitry. Expansion board designs should implement isolation circuitry as recommended in the block diagram below, and that meets the timing requirements of the table below and the timing diagram below.
Referring to the block diagram below, the isolation circuit block can also be used to level shift the module’s 1.8V IO signals to 3.3V or 5.0V logic levels, provided that the specifications of the table below are met.
Recommended Block Diagram for Boot Strap Signal Isolation
Example of a Delay Circuit you might use
PMIC_PWRGOOD to Isolation Circuitry Timing Diagram
PMIC_PWRGOOD and Boot Strap Signal Electrical Specifications
Parameter
Description
Min
Typ
Max
Units
T
DISABLE
Time between PMIC_PWRGOOD assertion to ENABLE_N deassertion (e.g. disabling of isolation circuit)
200
 
 
us
T
ENABLE
Time between PMIC_PWRGOOD deassertion to ENABLE_N assertion (e.g. enabling of the isolation circuit)
0
 
1
ms
R
ISOLATION_5V
Minimum Isolation Impedance (A to B) for 5V level shifting
800
 
 
kohms
R
ISOLATION_3.3V
Minimum Isolation Impedance (A to B) for 1.8V and 3.3V level shifting
500
 
 
kohms
See Also:

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.