Temperature dependent current limit control for fast-charging and safe operating area (SOA) protection

An apparatus, comprising:

• a power transistor including first and second current terminals and a first control input, the first current terminal connected to an input voltage node and the second current terminal connected to an output voltage node;
• a second transistor including third and fourth current terminals, the third current terminal connected to the input voltage node;
• a first resistor having first and second resistor terminals, the first resistor terminal connected to the fourth current terminal and the second resistor terminal connected to a ground node;
• a second resistor having third and fourth resistor terminals, the fourth resistor terminal connected to the fourth current terminal and to the first resistor terminal;
• a thermal limit circuit having a temperature sense circuit output node, the thermal limit circuit to generate an output signal on the thermal limit circuit output node that is based on a temperature of the power transistor;
• a first amplifier including a first input and a second input and a first amplifier output, the first input connected to the thermal limit circuit output node and to the third resistor terminal, and the second input connected to a reference signal node;
• and
• a third transistor including fifth and sixth current terminals and a control input, the control input of the third transistor connected to the first amplifier output, and the fifth current terminal coupled to the control input of the power transistor.

A system, comprising:

• a load;
• a capacitor connected to the load;
• a power transistor connected to the load and to the capacitor, the power transistor to conduct load current from a supply voltage node to the load and to the capacitor, the current to the capacitor charges the capacitor;
• a current sense circuit coupled to the power transistor, the current sense circuit to generate a current sense current proportional to the load current;
• a temperature sense circuit to generate a temperature sense voltage proportional to the temperature of the power transistor, the temperature sense circuit having a proportional to absolute temperature (PTAT) element that senses an internal core temperature of the power transistor;
• a thermal limit circuit coupled to the temperature sense circuit;
• and
• a current limit circuit coupled to the current sense circuit and to the thermal limit circuit, the current limit circuit to generate a control signal on a current limit circuit output node, the control signal responsive to the current sense current and to a first current from the thermal limit circuit, the current limit circuit output node coupled to a control input of the power transistor.