UNITRODE UCC2585, UCC3585 Technical data

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Low Voltage Synchronous Buck Controller

UCC2585 UCC3585

PRELIMINARY

FEATURES

Resistor Programmable 1.25V to 4.5V

•

OUT

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

3.2N

10k

549k

0.22µF C6

470pF

15 VIN

3 SS

100k

RTN

150µFC2150µF

147pF

ENB

COMP

VFB

ISET

0.47µF

CLSET

PDRV

ISENSE

NDRV

TRACK

N/C

PWRGND

GND

27.4k

Q1 IRF7404

L1 4.7µF

Q2 IRF7401

220µF

C10

C11 220µF

R12

32k

R10

36k

R11

82k

VOUT

RTN

07/99

UDG-98024

UCC2585 UCC3585

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 spec ified 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

CONNECTION DIAGRAMS

DIL-16, SOIC-16, SSOP-16 (TOP VIEW) J, N, D, and M Packages

ENB

VFB

GND

ISET

COMP

TRACK

CLSET

VIN

NDRV

PWRGND

PDRV

ISENSE

N/C

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 pro vide pulse-by-pulse limiting, timed shutdown after 7 con

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:

UCC3585, and T C

= 330pF, R

= –40°C to 85°C for the UCC2585. TA=TJ. VIN = 3.3V, ENB, I

= 100k, RTRACK = 10k, RCLSET = 10k.

ISET

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

= VIN,VFB= 1.25V, COMP = 1.5V,

SENSE

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 µA VIN Turn On Threshold (UVLO) 2.35 2.60 V VIN Turn On Hysteresis 450 550 mV

Voltage Amplifier Section

Input Voltage (Internal Reference) T

= 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) = –50µA 3.00 3.25 V Output Voltage Low I(COMP) = 50µA 0.10 0.25 V Output Source Current –100 –175 µA Output Sink Current 0.4 1.0 mA

Oscillator/PWM Section

Initial Accuracy T

= 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, V

= 1.6V 10 12 15 µA

TRACK

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 µA

Current Limit Section

Pulse to Pulse Threshold Measured Between V

and I

SENSE

100 125 150 mV CLSET Current 11 14 16 µA SD Sink Current SD = 2V 8 13 18 µA SD Source Current SD = 2V –100 –140 µA Restart Threshold Measured on SDOWN 0.40 0.55 0.90 V

Output Driver Section (PDRV, NDRV)

Pull Up Resistance –100mA (Source) T Pull Down Resistance 100mA (Sink) T

= 25°C6Ω

= 25°C4Ω

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 = V

–0.5.

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