Ttl Supply Monitor

040 TEST & MEASUREMENT The Type LTC1042 lc from Linear Technology is a window comparator that can function with very small currents. This is made possible by the use of sampling techniques that enable the disabling of certain parts of the is in the non-active phase. This economical behaviour is not so important in the present circuit: the monitor draws a current of rather more than the minimum 1004A. The comparator is set with the aid of a bandgap reference diode, Dl. The reference voltage of 2.5 V provided by this diode is connected direct to the window centre pin 2. The width of the window is also fixed with the aid of the refer- ence voltage. Since the circuit is intended to monitor a rn supply (5 V), the width of the window is arranged at one tenth of this, which is a convenient sub-multiple of the reference voltage. Po- tential divider R4-R5 gives a voltage of 0.25 V at half-window- width pin 5. This arrangement causes the within window output to go high when the input voltag...