Texas Instruments UCC3585N, UCC3585MTR, UCC3585M, UCC3585DTR, UCC3585D Datasheet

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UCC2585

UCC3585

PRELIMINARY

Low Voltage Synchronous Buck Controller

FEATURES

•Resistor Programmable 1.25V to 4.5V VOUT

•2.5V to 6V Input Supply Range

•1% DC Accuracy

•High Efficiency Synchronous Switching

•Drives P-channel (High Side) and N-channel (Low Side) MOSFETs

•Lossless Programmable Current Limit

•Logic Compatible Shutdown

•Programmable Frequency

•Start-up Voltage Tracking Protects Dual Rail Microprocessors

DESCRIPTION

The UCC2585/UCC3585 synchronous Buck controller provides flexible high efficiency power conversion for output voltages as low as 1.25V with guaranteed ±1% DC accuracy. Output currents are only limited by the choice of external logic level MOSFETs. With an input voltage range of 2.5V to 6.0V it is the ideal choice for 3.3V only, battery input, or other low voltage systems. Applications include local microprocessor core voltage power supplies for desktop and Notebook computers, and high speed GTL bus regulation. Its fixed frequency oscillator is capable of providing practical PWM operation to 700kHz.

With its low voltage capability and inherent “always on” operation, the UCC2585/UCC3585 causes VOUT to track VIN once VIN has exceeded the threshold voltage of the external P channel MOSFET. Tracking can be tailored for any application with a single resistor or disabled by connecting TRACK to VIN. For dual supply rail microprocessors this feature negates the need for external diodes to insure supply voltage tracking between the +3.3V and lower voltage microprocessor core supplies.

(continued)

TYPICAL APPLICATION DIAGRAM

VIN

0.47 F

27.4k

10k

VIN

CLSET

150

ENB

PDRV

IRF7404

L1 4.7 F

147pF

549k

COMP

ISENSE

VOUT

IRF7401

VFB

NDRV

C10

C11

TRACK

220 F

3.2N

R12

R10

N/C

32k

36k

0.22

PWRGND

470pF

ISET

GND

R11

82k

100k

RTN

UDG-98024

07/99

ABSOLUTE MAXIMUM RATINGS

Analog Pins

Minimum and Maximum Forced Voltage

(Reference to GND) . . . . . . . . . . . . . . . . . . . –0.3V to +6.3V Digital Pins

Minimum and Maximum Forced Voltage

(Reference to GND) . . . . . . . . . . . . . . . . . . . . .–0.3V to 6.3V Power Driver Output Pins

Maximum forced current . . . . . . . . . . . . . . . . . . . . . . . . . ± 1.0A Operating Junction Temperature . . . . . . . . . . –55°C to +125°C Storage Temperature. . . . . . . . . . . . . . . . . . . –65°C to +150°C

Note: Unless otherwise indicated, voltages are reference to ground and currents are positive into, negative out of, the specified terminals. Pulsed is defined as a less than 10% duty cycle with a maximum duration of 500ns.

APPLICATIONS

•Low Voltage Microprocessor Power such as PowerPC 603 and 604

•High Power 5V or 3.3V to 1.25V–4.5V Regulators

•GTL Bus Termination

DESCRIPTION (cont.)

The UCC2585/UCC3585 drives a complementary pair of power MOSFET transistors, P-channel on the high side, and N-channel on the low side to step down the input voltage at up to 90% efficiency.

A programmable two-level current limiting function is provided by sensing the voltage drop across the high side P channel MOSFET. This circuit can be configured to provide pulse-by-pulse limiting, timed shutdown after 7 con-

UCC2585

UCC3585

CONNECTION DIAGRAMS

DIL-16, SOIC-16, SSOP-16 (TOP VIEW)

J, N, D, and M Packages

			CT

ENB	1	16
			VIN

COMP	2	15
SS			NDRV

	3	14


VFB	4	13	PWRGND


GND	5	12	PDRV


TRACK	6	11	ISENSE


ISET	7	10	SD


CLSET	8	9	N/C

secutive faults, or latch-off after fault detection, allowing maximum application flexibility. The current limit threshold is programmed with a single resistor selected to match system MOSFET characteristics.

The UCC2585/UCC3585 also includes undervoltage lockout, a logic controlled enable, and softstart functions. The UCC2585/UCC3585 is offered in the 16 pin surface mount and through hole packages.

UCC2585

UCC3585

ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications hold for TA = 0°C to 70°C for the

UCC3585, and TA = –40°C to 85°C for the UCC2585. TA = TJ. VIN = 3.3V, ENB, ISENSE = VIN, VFB = 1.25V, COMP = 1.5V, CT = 330pF, RISET = 100k, RTRACK = 10k, RCLSET = 10k.

PARAMETER	TEST CONDITIONS	MIN	TYP	MAX	UNITS
Input Supply Section
Supply Current – Total (Active)			2.3	3.5	mA
Supply Current – Shutdown	ENABLE = 0V		10	25	µ A
VIN Turn On Threshold (UVLO)			2.35	2.60	V
VIN Turn On Hysteresis			450	550	mV
Voltage Amplifier Section
Input Voltage (Internal Reference)	TA = 0°C to 70°C, VIN = 3.0V to 3.6V, Note 1	1.238	1.250	1.262	V
Input Voltage (Internal Reference)	VIN = 3.0V to 3.6V, IND/MIL Temp, Note 1	1.228	1.250	1.273	V
Open Loop Gain	COMP = 0.5 to 2.5V	65	80		dB
Output Voltage High	I(COMP) = –50µ A	3.00	3.25		V
Output Voltage Low	I(COMP) = 50µ A		0.10	0.25	V
Output Source Current		–100	–175		µ A
Output Sink Current		0.4	1.0		mA
Oscillator/PWM Section
Initial Accuracy	TJ = 25°C	405	450	495	kHz
Initial Accuracy	Over Temperature	390	450	510	kHz
CT Ramp Peak to Valley		1.8	2.1	2.4	V
CT Ramp Valley Voltage		0.3	0.4		V
PWM Maximum Duty Cycle	COMP = 3V, Measured on PDRV	100			%
PWM Minimum Duty Cycle	COMP = 0.2V, Measured on PDRV			0	%
PWM Delay to Outputs	COMP = 2.5V		45		ns
Tracking Current	Measured on TRACK, VTRACK = 1.6V	10	12	15	µ A
Enable High Threshold	Measured on ENABLE (Note 3)		2.8		V
Enable Low Threshold	Measured on ENABLE		0.5		V
Softstart Charge Current	SS = 0V	–10	–14	–18	µ A
Current Limit Section
Pulse to Pulse Threshold	Measured Between VIN and ISENSE	100	125	150	mV
CLSET Current		11	14	16	µ A
SD Sink Current	SD = 2V	8	13	18	µ A
SD Source Current	SD = 2V		–100	–140	µ A
Restart Threshold	Measured on SDOWN	0.40	0.55	0.90	V
Output Driver Section (PDRV, NDRV)
Pull Up Resistance	–100mA (Source) TA = 25° C		6		Ω
Pull Down Resistance	100mA (Sink) TA = 25° C		4		Ω
Deadtime Delay	Note 2	150	200	250	ns

Note 1. Measured on COMP with the Error Amp in a Unity Gain (voltage follower) configuration.

Note 2. 50% point of PDRV Rise to NDRV Rise and 50% point of NDRV Fall to PDRV Fall.

Note 3. Enable High Threshold = VIN –0.5.

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