Micro Linear Corporation ML4903CT Datasheet

July 1999

ML4903

High Current Synchronous Buck Controller

GENERAL DESCRIPTION

The ML4903 high current synchronous buc k controller
provides high efficiency DC/DC conversion to generate
V

for processors such as the Pentium® Pro and Pentium

CCP

II from Intel

®

.

The ML4903 controller, when combined with two external
MOSFETs, generates output voltages between 1.8V and

3.5V from a 12V supply. The output voltage is selected via
an internal 2 chord 4-bit DAC. In the upper range, the
output can be set between 2.1V and 3.5V in 100mV steps.
In the lower range, the output can be set between 1.8V
and 2.05V in 50mV steps. Output currents in excess of
20A can be attained at efficiencies greater than 80%.

The ML4903 can be enabled/disabled via the SHDN pin.
While disabled, the output of the regulator is completely
isolated from the circuit’s input supply. The ML4903
employs fixed-frequency PWM control combined with a
sophisticated control loop enhancement circuit to provide
excellent load transient response.

BLOCK DIAGRAM

FEATURES

■ Designed to meet Pentium Pro and Pentium II VRM

power supply requirements

■ DC regulation to +1% maximum

■ Proprietary circuitry provides transient response of ±5%

maximum over a 0A to 14A load range

■ Programmable output voltage (1.8V to 3.5V) is set by

an onboard 2 chord 4-bit D AC

■ Synchronous buck topology for maximum power

conversion efficiency

■ Fixed frequency operation for easier system integration

■ Integrated anti-shootthrough logic, short circuit

protection, shutdown, and UV lockout

V

DD

19

V

CC

18

PROTECT

20

SHDN

6

D0

1

D1

2

D2

3

D3

4

RANGE

5

10.5V

4.4V

30µA

+
–

+
–

5V

3.5V

2 CHORD
4 BIT DAC

V

DAC

V

DAC

UVLO

+ 3%

V

- 3%

P DRV

17

CONTROL

LOGIC

+
–

V

DAC

+
–

FB

+
–

V

V

DAC

V

DAC

DAC

V

DAC

+ 10%

+ 3%

- 10%

- 3%

+
–

200kHz

–

+

+
–

+

V

FB

–

+
–

3.5V

REFERENCE

10

PWR GND

V

DAC

-107mV

PWR GOOD

GND

N DRV

COMP

V

I

SENSE

V

REF

16

15

13

FB

11

12

8

9

1

ML4903

PIN CONFIGURATION

ML4903

20-Pin TSSOP (T20)

D0

D1

D2

D3

RANGE

SHDN

NC

PWR GOOD

V

REF

GND

1

2

3

4

5

6

7

8

9

10

PIN DESCRIPTION

PIN NAME FUNCTION

1 D0 LSB input to the DAC which sets the

output voltage

2 D1 Input to the DAC which sets the

output voltage

3 D2 Input to the DAC which sets the

output voltage

20

19

18

17

16

15

14

13

12

11

TOP VIEW

PIN NAME FUNCTION

9V

REF

PROTECT

V

DD

V

CC

P DRV

N DRV

PWR GND

NC

COMP

I

SENSE

V

FB

Bypass connection for the internal

3.5V reference
1 0 GND Analog signal ground
11 V
12 I

FB

SENSE

Output voltage feedback pin
Current sense input

4 D3 MSB input to the DAC which sets the

output voltage

5 RANGE Range selection bit for the 2 chord 4-

bit DAC. Logic 1 sets the range at

2.1V to 3.5V with an LSB of 100mV.
Logic 0 sets the range at 1.8V to

2.05V with an LSB of 50mV.

6 SHDN Grounding this pin shuts down the

regulator

8 PWR GOODThis open drain output goes low

whenever SHDN goes low or when
the output is not within +10% of its
nominal value

1 3 COMP Connection for the compensation and

optional soft-start delay network
15 PWR GND Power ground
1 6 N DRV Synchronous rectifier driver output
1 7 P DRV Buck switch driver output
18 V

CC

Connection point for monitoring the

5V supply to determine the proper

condition of PWR GOOD
19 V

DD

12V power supply input

20 PROTECT Connection for the integrating current

limit network

2

ABSOLUTE MAXIMUM RATINGS

ML4903

Absolute maximum ratings are those values beyond which
the device could be permanently damaged. Absolute
maximum ratings are stress ratings only and functional
device operation is not implied.

V

...........................................................................................

DD

V

..................................................................................................7V

CC

13.5V

Peak Dri ver Output Current.......................................±2A

Voltage...................................... GND - 0.3V to 5.5V

V

FB

I

Voltage.................................. GND - 0.5V to 5.5V

SENSE

All Other Inputs .................... GND - 0.3V to VDD + 0.3V

SHDN Input Current .............................................. 100mA

Junction T emperature.............................................. 150°C

Storage Temperature Range ..................... –65°C to 150°C

Lead Temperature (Soldering, 10 sec) .....................260°C

Thermal Resistance (

qJA).................................... 100°C/W

OPERATING CONDITIONS

T emper ature Range .......................................0°C to 70°C

VDD Range ..............................................11.4V to 12.6V

Range ...............................................4.75V to 5.25V

V

CC

ELECTRICAL CHARACTERISTICS

Unless otherwise specified, VDD = 12V, VCC = SHDN = 5V, TA = Operating Temperature Range (Note 1)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

REFERENCE

V

Output Voltage 3.51 3.535 3.56 V

REF

Line Regulation 11V < VDD < 13V 0.5 mV/V

UV LOCKOUT

VDD Start-up Threshold 10.0 10.5 10.8 V
VDD Hysteresis 30 0 450 6 00 mV
VCC Start-up Threshold 4.25 4.4 4.6 V
VCC Hysteresis 30 0 400 50 0 mV

SHUTDOWN

Input Low Voltage 0.8 V
Input High Voltage 2.0 V
Delay to Output 50 ns

POWER GOOD COMPARATOR

Output Voltage in Regulation 5kW pull-up to 5V 4.8 V
Output Voltage out of Regulation VFB < 90% V
Output Voltage in Shutdown SHDN = 0V, 5kW pull-up to 5V 0.4 V

BUCK REGULATOR

Oscillator Frequency 160 200 230 kHz
Duty Cycle Ratio RANGE = 1, V

or >110% V

DAC

= 0V, 80 98 %

DAC (D3-D0) Code = 0100
RANGE = 1, VFB > 3.193V, 0 %

DAC (D3-D0) Code = 0100

FB

DAC

0.4 V

DAC (RANGE, D3-D0) Input Low Voltage 0.8 V
DAC (RANGE, D3-D0) Input High Voltage 2.0 V

3

ML4903

ELECTRICAL CHARACTERISTICS (Continued)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

BUCK REGULATOR (Continued)

VFB Threshold Voltage (Note 2) RANGE = 0, (D3-D0) Code = 0000 2.050 2.071 2.092 V

RANGE = 0, (D3-D0) Code = 0001 2.000 2.020 2.04 V
RANGE = 0, (D3-D0) Code = 0010 1.950 1.970 1.989 V
RANGE = 0, (D3-D0) Code = 0011 1.900 1.919 1.938 V
RANGE = 0, (D3-D0) Code = 0100 1.850 1.869 1.887 V
RANGE = 0, (D3-D0) Code = 0101 1.800 1.818 1.836 V
RANGE = 1, (D3-D0) Code = 0000 3.500 3.535 3.570 V
RANGE = 1, (D3-D0) Code = 0001 3.400 3.434 3.468 V
RANGE = 1, (D3-D0) Code = 0010 3.300 3.333 3.366 V
RANGE = 1, (D3-D0) Code = 0011 3.200 3.232 3.264 V
RANGE = 1, (D3-D0) Code = 0100 3.100 3.131 3.162 V
RANGE = 1, (D3-D0) Code = 0101 3.000 3.030 3.060 V
RANGE = 1, (D3-D0) Code = 0110 2.900 2.929 2.958 V

SUPPLY

I

DD

RANGE = 1, (D3-D0) Code = 0111 2.800 2.828 2.856 V
RANGE = 1, (D3-D0) Code = 1000 2.700 2.727 2.754 V
RANGE = 1, (D3-D0) Code = 1001 2.600 2.626 2.652 V
RANGE = 1, (D3-D0) Code = 1010 2.500 2.525 2.550 V
RANGE = 1, (D3-D0) Code = 1011 2.400 2.424 2.448 V
RANGE = 1, (D3-D0) Code = 1100 2.300 2.323 2.346 V
RANGE = 1, (D3-D0) Code = 1101 2.200 2.222 2.244 V
RANGE = 1, (D3-D0) Code = 1110 2.100 2.121 2.142 V

I

Threshold Voltage -80 -117 mV

SENSE

I

Hysteresis 10 mV

SENSE

PROTECT Threshold Voltage 3.2 3.5 3.8 V
PROTECT Hysteresis 1.8 2 2.2 V
PROTECT Charging Current V(I
PROTECT Leakage Current +100 nA
Transition Time, C

P DRV and N DRV

VDD Current SHDN = 0V 650 900 µA

DAC (D3-D0) Code = 0000

) = -120mV 30 µA

SENSE

= 5000pF, 10-90% 40 ns

L

SHDN = 5V, VFB = 5V 1 2 mA
SHDN = 5V, VFB = 0V, CL = 5000pF 20 mA

I

Note 1: Limits are guaranteed by 100% testing, sampling, or correlation with worst case test conditions.
Note 2: Codes 00110 to 01111, and 11111 are not valid; applying these codes to the DAC will shut off P DRV and N DRV.

VCC Current 110µA

CC

4