regulator: ltc3589: Add DT binding documentation

Linear Technology LTC3589, LTC3589-1, and LTC3589-2 8-output regulators

Required properties:

- compatible: "lltc,ltc3589", "lltc,ltc3589-1" or "lltc,ltc3589-2"

- reg: I2C slave address

Required child node:

- regulators: Contains eight regulator child nodes sw1, sw2, sw3, bb-out,

  ldo1, ldo2, ldo3, and ldo4, specifying the initialization data as

  documented in Documentation/devicetree/bindings/regulator/regulator.txt.

Each regulator is defined using the standard binding for regulators. The

nodes for sw1, sw2, sw3, bb-out, ldo1, and ldo2 additionally need to specify

the resistor values of their external feedback voltage dividers:

Required properties (not on ldo3, ldo4):

- lltc,fb-voltage-divider: An array of two integers containing the resistor

  values R1 and R2 of the feedback voltage divider in ohms.

Regulators sw1, sw2, sw3, and ldo2 can regulate the feedback reference from

0.3625 V to 0.75 V in 12.5 mV steps. The output voltage thus ranges between

0.3625 * (1 + R1/R2) V and 0.75 * (1 + R1/R2) V. Regulators bb-out and ldo1

have a fixed 0.8 V reference and thus output 0.8 * (1 + R1/R2) V. The ldo3

regulator is fixed to 1.8 V on LTC3589 and to 2.8 V on LTC3589-1,2. The ldo4

regulator can output between 1.8 V and 3.3 V on LTC3589 and between 1.2 V

and 3.2 V on LTC3589-1,2 in four steps. The ldo1 standby regulator can not

be disabled and thus should have the regulator-always-on property set.

Example:

	ltc3589: pmic@34 {

		compatible = "lltc,ltc3589-1";

		reg = <0x34>;

		regulators {

			sw1_reg: sw1 {

				regulator-min-microvolt = <591930>;

				regulator-max-microvolt = <1224671>;

				lltc,fb-voltage-divider = <100000 158000>;

				regulator-ramp-delay = <7000>;

				regulator-boot-on;

				regulator-always-on;

			};

			sw2_reg: sw2 {

				regulator-min-microvolt = <704123>;

				regulator-max-microvolt = <1456803>;

				lltc,fb-voltage-divider = <180000 191000>;

				regulator-ramp-delay = <7000>;

				regulator-boot-on;

				regulator-always-on;

			};

			sw3_reg: sw3 {

				regulator-min-microvolt = <1341250>;

				regulator-max-microvolt = <2775000>;

				lltc,fb-voltage-divider = <270000 100000>;

				regulator-ramp-delay = <7000>;

				regulator-boot-on;

				regulator-always-on;

			};

			bb_out_reg: bb-out {

				regulator-min-microvolt = <3387341>;

				regulator-max-microvolt = <3387341>;

				lltc,fb-voltage-divider = <511000 158000>;

				regulator-boot-on;

				regulator-always-on;

			};

			ldo1_reg: ldo1 {

				regulator-min-microvolt = <1306329>;

				regulator-max-microvolt = <1306329>;

				lltc,fb-voltage-divider = <100000 158000>;

				regulator-boot-on;

				regulator-always-on;

			};

			ldo2_reg: ldo2 {

				regulator-min-microvolt = <704123>;

				regulator-max-microvolt = <1456806>;

				lltc,fb-voltage-divider = <180000 191000>;

				regulator-ramp-delay = <7000>;

				regulator-boot-on;

				regulator-always-on;

			};

			ldo3_reg: ldo3 {

				regulator-min-microvolt = <2800000>;

				regulator-max-microvolt = <2800000>;

				regulator-boot-on;

			};

			ldo4_reg: ldo4 {

				regulator-min-microvolt = <1200000>;

				regulator-max-microvolt = <3200000>;

			};

		};

	};