2DW23x Zeners - testing resistors (part 9)
resistors used,
- Vishay ptf56-Z (5ppm/C) for OP feedback divider and temp-set divider.
- Vishay z201 (0.2ppm/C) for 200ohm current limit resistor.
- Bourns 3250w for t-set fine adjustment.
Plot from cold-start to operating temperature. t-set is adjusted to coincide with TC0 around 60C case temperature. Zener current is around 26mA.
Plot of z-sense versus the on-die t-sense over approximately 20 hours. Zener sense variation is independent of 2DW232 operating temperature - indicating correct function of 2DW232 temperature stabilization.
But the zener sense V is strongly correlated with ambient temperature - indicating unstabilized components are problematic. Almost 100uV over 5C.
With zener sense V plotted directly against temperature
Resistor sensitivity can also be tested by spraying them with isopropyl alcohol and observing any change in the reference voltage due to evaporative cooling.
Cooling the z201 shows no obvious change.
However the ptf256 used for the main OP feedback divider generates up to 200uV change in Zener output voltage.