This section explains the voltage regulator current limiter characteristic VOUT vs IOUT) method.
The same current limiter function is also used for switching power supplies (DC/DC and AC/DC), etc.
Current limiter classification
The current limiters built into voltage regulators can be classified into 4 main types.
A) Drooping type current limiter ⇒ Foldback current limiter
B) Foldback current limiter only
C) Drooping type current limiter ⇒ Drooping type current limiter
D) Foldback type current limiter ⇒ Drooping type current limiter
For example, for Type A, the drooping type current limiter initially activates and then is followed by the activation of the foldback current limiter, so this is expressed as “A) Drooping type current limiter ⇒ Foldback current limiter.”


Current limiter history and characteristics
A) Drooping type current limiter ⇒ Foldback current limiter
Conventional voltage regulators (XC6204, XC6219, etc.) employed Type A (Drooping type ⇒ Foldback). This foldback current limiter was not sufficiently accurate, however, so a drooping type current limiter was added.
B) Foldback current limiter only
Later, high-accuracy control became possible using just a foldback limiter.
This led to the commercialization of Type B (Foldback only) voltage regulators, which employed a foldback limiter that can detect overcurrent.
With foldback limiters, however, if there is even a slight negative output voltage before startup, there is a possibility the output voltage cannot be started.
This is because if the output voltage is negative, the amount of current that can be supplied by the voltage regulator is 0mA, which could cause the circuit to balance while current is not being supplied to the output side.
C) Drooping type current limiter ⇒ Drooping type current limiter
The foldback current startup problem can be avoided by using a voltage regulator that employs a drooping type current limiter during a short circuit. This is the background behind the introduction of the Type C (Drooping type ⇒ Drooping Type) voltage regulator (XC6223, XC6503, etc.).
Additionally, the drooping type current limiter provides excellent control of the current limit value.
With the Type C voltage regulator, the current limit value is constant when the output voltage is 1V or higher, so the heater generation is greater than with Types A and B, so there is a problem with junction temperature increase during current limitation.
Further, the junction temperature increase problem can be countered by building in a thermal shutdown function.
D) Foldback type current limiter ⇒ Drooping type current limiter
In regards to the junction temperature increase during current limiting, which is a problem with Type C (Drooping type ⇒ Drooping type), employing a Type D (Foldback ⇒ Drooping Type) current limiter generates less heat during current limiting than does Type C.
List of Types of Voltage Regulator Current Limiters
TYPE A
(Drooping type ⇒Foldback)TYPE B
(Foldback only)TYPE C
(Drooping type ⇒ Drooping type)TYPE D
(Foldback ⇒ Drooping type)XC6231
XC6224
XC6220
XC6219
XC6213
XC6210
XC6209
XC6206
XC6205
XC6204
XC6504
XC6601XC6242
XC6241
XC6240
XC6227
XC6225
XC6222
XC6221
XC6218
XC6217
XC6216
XC6215
XC6214
XC6206
XC6506
XC6501
XC6604
XC6603
XC6602
XC6706
XC6705
XC6702
XC6701
XC6902
XC6901XC6230
XC6229
XC6228
XC6223
XC6505XC6233
XC6505
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