July 1999
ML4903
High Current Synchronous Buck Controller
GENERAL DESCRIPTION
The ML4903 high current synchronous buck controller
provides high efficiency DC/DC conversion to generate
V
CCP
for processors such as the Pentium
庐
Pro and Pentium
II from Intel
庐
.
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鈥檚 input supply. The ML4903
employs fixed-frequency PWM control combined with a
sophisticated control loop enhancement circuit to provide
excellent load transient response.
FEATURES
s
Designed to meet Pentium Pro and Pentium II VRM
power supply requirements
DC regulation to +1% maximum
Proprietary circuitry provides transient response of 卤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 DAC
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
s
s
s
s
s
s
BLOCK DIAGRAM
19
VDD
+
10.5V
18
鈥?/div>
VCC
UVLO
+
P DRV
17
4.4V
5V
30碌A
PROTECT
20
鈥?/div>
CONTROL
LOGIC
N DRV
16
3.5V
+
鈥?/div>
+
鈥?/div>
PWR GND
15
SHDN
6
COMP
200kHz
鈥?/div>
13
D0
1
VFB
11
D1
2
+
VDAC
-107mV
I
SENSE
PWR GOOD
8
D2
3
+
鈥?/div>
12
D3
4
RANGE
5
2 CHORD
4 BIT DAC
VDAC
+
鈥?/div>
VDAC + 10%
VDAC + 3%
VFB
VDAC - 10%
VDAC - 3%
10
+
鈥?/div>
VDAC + 3%
VFB
VDAC - 3%
+
鈥?/div>
+
鈥?/div>
3.5V
REFERENCE
GND
VREF
9
1
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