[MKRNBV3] Reduce USB voltage limit to 3880mV

On module powerup there can be current spikes that make the USB voltage drop under 4.36V. This results in PGOOD fault and module lockup.
Only V3 seems affected, and FW A.02.01 even more.

Author: facchinm

variants/mkrnb1500/variant.cpp

@@ -182,6 +182,7 @@ SERCOM sercom5(SERCOM5);
 #include "wiring_private.h"
 
 #define PMIC_ADDRESS  0x6B
+#define PMIC_REG00    0x00
 #define PMIC_REG01    0x01
 #define PMIC_REG07    0x07
 
@@ -199,6 +200,20 @@ static inline void enable_battery_charging() {
   PERIPH_WIRE.disableWIRE();
 }
 
+static inline void set_voltage_current_thresholds() {
+  PERIPH_WIRE.initMasterWIRE(100000);
+  PERIPH_WIRE.enableWIRE();
+  pinPeripheral(PIN_WIRE_SDA, g_APinDescription[PIN_WIRE_SDA].ulPinType);
+  pinPeripheral(PIN_WIRE_SCL, g_APinDescription[PIN_WIRE_SCL].ulPinType);
+
+  PERIPH_WIRE.startTransmissionWIRE( PMIC_ADDRESS, WIRE_WRITE_FLAG );
+  PERIPH_WIRE.sendDataMasterWIRE(PMIC_REG00);
+  PERIPH_WIRE.sendDataMasterWIRE(0x06); // 3.880 V + 2A ILIM
+  PERIPH_WIRE.prepareCommandBitsWire(WIRE_MASTER_ACT_STOP);
+
+  PERIPH_WIRE.disableWIRE();
+}
+
 static inline void disable_battery_fet(bool disabled) {
   PERIPH_WIRE.initMasterWIRE(100000);
   PERIPH_WIRE.enableWIRE();
@@ -230,6 +245,7 @@ void initVariant() {
     enable_battery_charging();
   }
   disable_battery_fet(!batteryPresent);
+  set_voltage_current_thresholds();
 #endif
 
   // power off the module