Datasheet

/EN
POWER
SUPPLY
V
out
VOUT
VFB
Rmrg_HI
VFB
Rmrg_LO
10k
3.3V
Open Loop Margining
MON(1:12)
GPIO(1:12)
UCD90124A
GPIO
GPIO
/EN
POWER
SUPPLY
Vout
VOUT
VFB
Rmrg_HI
VFB
Rmrg_LO
10k
3.3V
“0” or “1 ”
“0” or “1 ”
W
W
VOUT
VOUT
3.3V
.
3.3V
MON(1:12)
GPIO
UCD90124A
Vout
R3
Vmarg
C1
R4
FPWM1
V
FB
10k
3.3 V
Closed Loop
Margining
250 kHz – 1MHz
/EN
POWER
SUPPLY
VOUT
VFB
W
R1
R2
UCD90124A
www.ti.com SLVSAN8 –JANUARY 2012
Figure 21. Open-Loop Margining
Closed-Loop Margining
Closed-loop margining uses a PWM or FPWM output for each power supply that is being margined. An external
RC network converts the FPWM pulse train into a DC margining voltage. The margining voltage is connected to
the appropriate power-supply feedback node through a resistor. The power-supply output voltage is monitored,
and the margining voltage is controlled by adjusting the PWM duty cycle until the power-supply output voltage
reaches the margin-low and margin-high voltages set by the user. The voltage setting resolutions will be the
same that applies to the voltage measurement resolution (Table 3). The closed loop margining can operate in
several modes (Table 6). Given that this closed-loop system has feed back through the ADC, the closed-loop
margining accuracy will be dominated by the ADC measurement. The relationship between duty cycle and
margined voltage is configurable so that voltage increases when duty cylce increases or decreases. For more
details on configuring the UCD90124A for margining, see the Voltage Margining Using the UCD9012x application
note (SLVA375).
Table 6. Closed Loop Margining Modes
Mode Description
DISABLE Margining is disabled.
ENABLE_TRI_STATE When not margining, the PWM pin is set to high impedance state.
When not margining, the PWM duty-cycle is continuously adjusted to keep the voltage at
ENABLE_ACTIVE_TRIM
VOUT_COMMAND.
ENABLE_FIXED_DUTY_CYCLE When not margining, the PWM duty-cycle is set to a fixed duty-cycle.
Figure 22. Closed-Loop Margining
FAN CONTROL
The UCD90124A can control and monitor up to four two-, three- or four-wire fans. Up to four GPIO pins can be
used as tachometer inputs. The number of fan tach pulses per revolution for each fan can be entered using the
Fusion GUI. A fan speed-fault threshold can be set to trigger an alarm if the measured speed drops below a
user-defined value.
The two- and three-wire fans are controlled by connecting the positive input of the fan to the specified supply
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