Battery powered diagnostics
Original Publication Date: 2005-Mar-09
Included in the Prior Art Database: 2005-Mar-09
One of the service features for the xSeries computers is the LightPath diagnostics. This feature allows a service technician to light a set of diagnostic LEDs, indicating the area of trouble when the system is unpowered. Since this is typically done with the blade removed from the system and completely unpowered, a large storage capacitor is required to provide the necessary energy to light the LEDs for the required minimum time. This capacitor is necessarily large, taking up a large amount of board space. A method of powering the diagnostics, which eliminates the need for the large storage capacitor, is described. This method is a more compact solution, saving precious board space, at a reduced cost.
Battery powered diagnostics
Figure 1 shows a typical solution for providing the power to drive the LightPath LEDs in an xSeries server. C711, the 1F capacitor, is charged to a voltage while the system is powered normally. This voltage, CAPPWR in Figure 1, powers a pair of PCA9557s (not shown in the figure) and LEDPWR powers the diagnostic LEDs (not shown in the figure) when SW4 is depressed. When a fault occurs, a diagnostic code is stored in the PCA9557s by the system. During a service call, the service technician removes the blade from the chassis, which causes all system voltages to be removed from the board. At this time the charge stored on C711 is used to power the PCA9557s (CAPPWR). At some time after removing the blade from the chassis the service technician presses the pushbutton switch to view the diagnostic codes. With the button depressed, C711 provides the power to light the LEDs (LEDPWR). To allow adequate time for the technician to read the codes, C711 must provide sufficient charge to light the LEDs for a minimum of 30 seconds. In addition, C711 must have sufficient charge to power the PCA9557s for 2 hours to allow time for a technician to service the blade. The capacitor required to store sufficient charge to provide this power is a relatively large and costly capacitor.
Another solution for the LightPath diagnostics power takes advantage of the real
time clock battery present on the board to eliminate the requirement of the 1F storage
capacitor, without significantly affecting the battery life. Figure 2 shows one possible
implementation of this disclosure. SW4 serves the same function as SW4 in Figure 1 .
Operation of the circuit in Figure 2 is as follows. Prior to first being installed in a
chassis, Q1 and Q2 will be off, isolating the battery from the diagnostic circuit. Once the
blade is plugged into a chassis, C2 is charged close to 12V and C1 is charged close to
3.3V and Q1 and Q2 are still off. The PCA9557s are powered by the 3.3V rail (CAPPWR) through CR3 so at this time, no additional load is placed on the battery by the diagnostic circuits. When a fault occurs, it is latched in the PCA9557s,...