FAN5094MTCX Fairchild Semiconductor, FAN5094MTCX Datasheet - Page 16

• Manufacturer Part Number: FAN5094MTCX
• Description: IC CTRLR DC/DC SYNC BUCK 28TSSOP
• Manufacturer: Fairchild Semiconductor

Specifications of FAN5094MTCX

• Applications: Controller, Intel Pentium® IV
• Voltage - Input: 12V
• Number Of Outputs: 1
• Voltage - Output: 1.1 ~ 1.85 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP
• Output Voltage: 1.85 V
• Output Current: 60 A
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: FAN5094MTCXTR; FAN5094MTCX_NL; FAN5094MTCX_NLTR; FAN5094MTCX_NLTR

FAN5094
tively, of the appropriate low-side MOSFET. Care is required
in the layout of these grounds; see the layout guidelines in
this datasheet.
Current Sharing
The two independent current sensors of the FAN5094 operate
with their independent current control loops to guarantee that
the two phases each deliver half of the total output current.
The only mismatch between the two phases occurs if there is
a mismatch between the R
In normal usage, two FAN5094s will be operated in parallel.
By connecting the ISHR pins together, the two error amps of
the two ICs will be forced to operate at exactly the same duty
cycle, thus ensuring very close matching of the currents of
all four phases.
Short Circuit Current Characteristics
The FAN5094 short circuit current characteristic includes a
function that protects the DC-DC converter from damage in
the event of a short circuit. The short circuit limit is given by
the formula
per phase.
Precision Current Sensing
The tolerances associated with the use of MOSFET current
sensing can be circumvented by the use of a current sense
resistor.
Light Load Efficiency
At light load, the FAN5094 uses a number of techniques to
improve efficiency. Because a synchronous buck converter is
two quadrant, able to both source and sink current, during
light load the inductor current will flow away from the out-
put and towards the input during a portion of the switching
cycle. This reverse current flow is detected by the FAN5094
as a positive voltage appearing on the low-side MOSFET
during its on-time. When reverse current flow is detected, the
low-side MOSFET is turned off for the rest of the cycle, and
the current instead flows through the body diode of the
high-side MOSFET, returning the power to the source. This
technique substantially enhances light load efficiency.
E*-mode
In addition, further enhancement in efficiency can be obtained
by putting the FAN5094 into E*-mode. When the Droop pin
is pulled to the 5V BYPASS voltage, the “A” phase of the
FAN5094 is completely turned off, reducing in half the
amount of gate charge power being consumed. E*-mode can
be implemented with the circuit shown in Figure 4:
16
I
SC
=
DS,on
------------------------------- -
10 R
of the low-side MOSFETs.
6V
DS on
Note that the charge pump for the HIDRVs should be based
on the “B” phase of the FAN5094, since the “A” phase is off
in E*-mode.
Internal Voltage Reference
The reference included in the FAN5094 is a precision band-
gap voltage reference. Its internal resistors are precisely
trimmed to provide a near zero temperature coefficient (TC).
Based on the reference is the output from an integrated 5-bit
DAC. The DAC monitors the 5 voltage identification pins,
VID0-4, and scales the reference voltage from 1.100V to
1.850V in 25mV steps.
BYPASS Reference
The internal logic of the FAN5094 runs on 5V. To permit the
IC to run with 12V only, it produces 5V internally with a
linear regulator, whose output is present on the BYPASS pin.
This pin should be bypassed with a 1µF capacitor for noise
suppression. The BYPASS pin should not have any external
load attached to it.
Dynamic Voltage Adjustment
The FAN5094 has internal pullups on its VID lines. External
pullups should not be used. The FAN5094 can have its output
voltage dynamically adjusted to accommodate low power
modes. The designer must ensure that the transitions on the
VID lines all occur simultaneously (within less than
to avoid false codes generating undesired output voltages.
The Power Good flag tracks the VID codes, but has a
500µsec delay transitioning from high to low; this is long
enough to ensure that there will not be any glitches during
dynamic voltage adjustment.
Power Good (PWRGD)
The FAN5094 Power Good function is designed in accor-
dance with the Pentium IV DC-DC converter specifications
and provides a continuous voltage monitor on the VFB pin.
The circuit compares the VFB signal to the VREF voltage
and outputs an active-low interrupt signal to the CPU should
the power supply voltage deviate more than +15%/-8% of its
nominal setpoint. The output is guaranteed open-collector
high when the power supply voltage is within +8%/-15% of
its nominal setpoint. The Power Good flag provides no
control functions to the FAN5094.
HI = E*-
mode on
Figure 4. Implementing E*-mode Control
10K
10K
2N2222
10K
BYPASS
PRODUCT SPECIFICATION
2N2907
R
DROOP
REV. 1.0.2 5/13/02
FAN5094
pin25
nsec)