Micro Linear Corporation ML4900CS, ML4900CT Datasheet
July 2000
ML4900*
High Current Synchronous Buck Controller
GENERAL DESCRIPTION
The ML4900 high current synchronous buck controller has
been designed to provide high efficiency DC/DC
conversion for next generation processors such as the
Pentium® Pro from Intel®.
The ML4900 controller, when combined with two
N-channel MOSFETs, generates output voltages between
2.1V and 3.5V from a 5V supply. The output voltage is
selected via an internal 4-bit DAC. Output currents in
excess of 14A can be attained at efficiencies greater than
90%.
The ML4900 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 ML4900
employs fixed-frequency PWM control combined with a
dual mode control loop to provide excellent load transient
response.
BLOCK DIAGRAM
(Pin Configuration Shown for 16-Pin SOIC Version)
FEATURES
■ Designed to meet Pentium
requirements
■ DC regulation to +1% maximum
■ Proprietary circuitry provides transient response of +5%
maximum over 300mA to 14A load range
■ Programmable output voltage (2.1V to 3.5V) is set by
an onboard 4-bit DAC
■ Synchronous N-channel buck topology for maximum
power conversion efficiency
■ Fixed frequency operation for easier system integration
■ Integrated antishoot-through logic, short circuit
protection, and UV lockout
■ Shutdown control provides load isolation
(* Indicates Part is End of Life as of July 1, 2000)
®
Pro power supply
V
DD
15
PROTECT
16
SHDN
5
D0
1
D1
2
D2
3
D3
4
10.5V
35µA
4.4V
+
–
+
–
4 BIT DAC
V
DAC
V
DAC
4V
UVLO
+ 3%
V
- 3%
N DRV H
CONTROL
LOGIC
+
–
V
DAC
+
–
FB
+
–
V
V
DAC
V
DAC
DAC
V
DAC
+ 10%
+ 3%
- 10%
- 3%
+
–
200kHz
+
V
FB
–
+
–
REFERENCE
+
–
+
–
3.5V
PWR GND
V
DAC
-73mV
PWR GOOD
GND
8
N DRV L
COMP
V
I
SENSE
V
REF
14
13
12
11
FB
9
10
6
7
1
ML4900
PIN CONFIGURATION
ML4900
16-Pin Narrow SOIC (S16N)
D0
D1
D2
D3
SHDN
PWR GOOD
V
REF
GND
PIN DESCRIPTION
1
2
3
4
5
6
7
8
TOP VIEW
(Pin Number in Parentheses is for TSSOP Version)
PIN NAME FUNCTION
16
15
14
13
12
11
10
PROTECT
V
DD
N DRV H
N DRV L
PWR GND
COMP
ISENSE
9
V
FB
1 (1) D0 LSB input to the DAC which sets
the output voltage
2 (2) D1 Input to the DAC which sets the
output voltage
ML4900
20-Pin TSSOP (T20)
D0
D1
D2
D3
NC
SHDN
NC
PWR GOOD
V
REF
GND
1
2
3
4
5
6
7
8
9
10
TOP VIEW
PIN NAME FUNCTION
20
19
18
17
16
15
14
13
12
11
8 (10) GND Analog signal ground
9 (11) V
10 (12) I
FB
SENSE
Output voltage feedback pin
Current sense input
PROTECT
V
DD
NC
N DRV H
N DRV L
PWR GND
NC
COMP
I
SENSE
V
FB
3 (3) D2 Input to the DAC which sets the
output voltage
4 (4) D3 MSB input to the DAC which sets
the output voltage
5 (6) SHDN Grounding this pin shuts down the
regulator
6 (8) PWR GOOD This open collector output goes
low whenever SHDN goes low or
when the output is not within
+10% of its nominal value
7 (9) V
REF
Bypass connection for the internal
3.5V reference
11 (13) COMP Connection for the compensation
and optional soft-start delay
network
12 (15) PWR GND Power ground
13 (16) N DRV L Synchronous rectifier driver output
14 (17) N DRV H Buck switch driver output
15 (19) V
DD
12V power supply input
16 (20) PROTECT Connection for the integrating
current limit network and the
UVLO monitor for the 5V supply
2
ABSOLUTE MAXIMUM RATINGS
ML4900
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
.......................................................................................... 13.5V
DD
Lead Temperature (Soldering, 10 sec) ......................260ºC
Thermal Resistance (qJA)
16-Pin Narrow SOIC ...................................... 100ºC/W
20-Pin TSSOP ................................................. 143ºC/W
Peak Driver Output Current .......................................±2A
VFB Voltage....................................... GND - 0.3V to 5.5V
I
Voltage ................................... GND - 0.5V to 5.5V
SENSE
All Other Analog Inputs ..........GND - 0.3V to VDD + 0.3V
SHDN Input Current .............................................. 100mA
Junction Temperature .............................................. 150ºC
OPERATING CONDITIONS
Temperature Range........................................ 0ºC to 70ºC
VDD Range ...............................................11.4V to 12.6V
PROTECT (5V Supply) Range .................... 4.75V to 5.25V
Storage Temperature Range ...................... –65ºC to 150ºC
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, VDD = 12V, PROTECT = SHDN = 5V, TA = Operating Temperature Range (Note 1)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
REFERENCE
V
UV LOCKOUT
Output Voltage 3.51 3.535 3.56 V
REF
Line Regulation 11V < VDD < 13V 0.5 mV/V
VDD Start-up Threshold 10.2 10.5 10.8 V
VDD Hysteresis 300 450 600 mV
PROTECT (5V) Start-up Threshold 4.25 4.4 4.5 V
PROTECT (5V) Hysteresis 400 450 500 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 DAC (D3-D0) Code = 0100, 85 95 %
or >110% V
DAC
VFB = 0V
DAC (D3-D0) Code = 0100, 0 %
VFB > 3.193V
DAC
0.4 V
DAC (D3-D0) Input Low Voltage 0.8 V
DAC (D3-D0) Input High Voltage 2.0 V
3
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