The overvoltage circuit consist of a voltage detector(U1100) and a power switch(Q1100). A resistor divider network at the input of U1100 is used to set the EXT_B+

detect voltage to 6.75V nominal. U1100 outputs low whenever the input voltage is below the detector threshold. During normal operating voltages from EXT_B+ the

gate voltage of Q1100 is zero, which turns Q1100 on. Wh en Q1100 is on, SW_EXT_B+ i s connected to EXT_B+. When EXT_B+ voltage is above 7.0875V nominally,

U1100 output becomes open drain. This causes the gate of Q1100 to be pulled up to the EXT_B+, which turns Q1100 off and thus disconnects the voltage to

SW_EXT_B+. Q1102-A and Q11 02-B act as inverters. Therefore, a low state at the output od U1100 will result with a low state at the gate of Q1100 and vise versa.

The status LED is controlled by U1000 via CALL1 and CALL2. In order to enable either LED the corresponding Q1101 transistor is enabled, allowing the status LED to

be supplied by 2.75V.

P8190: