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ADM1052 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADM1052
Beschreibung Precision Dual Voltage Regulator Controller
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 8 Seiten
ADM1052 Datasheet, Funktion
a
FEATURES
Two Independent Controllers on One Chip
Two 2.525 V Outputs
Shutdown Inputs to Control Each Channel
؎2.5% Accuracy Over Line, Load, and Temperature
Low Quiescent Current
Low Shutdown Current
Works with External N-Channel MOSFETs for Low Cost
“Hiccup Mode” Fault Protection
No External Voltage or Current Setting Resistors
Small, 8-Lead SO Package
APPLICATIONS
Desktop Computers
Servers
Workstations
Precision Dual Voltage
Regulator Controller
ADM1052
GENERAL DESCRIPTION
The ADM1052 is a dual, precision, voltage regulator controller
intended for power rail generation and active bus termination
on personal computer motherboards. It contains a precision
1.2 V bandgap reference and two channels consisting of con-
trol amplifiers driving external power devices. Each channel has a
shutdown input to turn off amplifier output and “Hiccup Mode”
protection circuitry for the external power device.
The ADM1052 operates from a 12 V supply. This gives suffi-
cient headroom for the amplifiers to drive external N-channel
MOSFETs, operating as source-followers, as the external series
pass devices. This has the advantage that N-channel devices are
cheaper than P-channel devices of similar performance, and the
circuit is easier to stabilize than one using P-channel devices in
a common-source configuration.
SHDN1
ADM1052
VCC
50A
FUNCTIONAL BLOCK DIAGRAM
VCC
BANDGAP
REFERENCE
SHUTDOWN
CONTROL
HICCUP
COMPARATOR
3.3V
CONTROL
AMPLIFIER
FORCE 1
SENSE 1
100F
VOUT1
2 ؋ 100F
3.3V
SHDN2
VCC
50A
VCC
CONTROL
AMPLIFIER
FORCE 2
SENSE 2
SHUTDOWN
CONTROL
HICCUP
COMPARATOR
100F
VOUT2
2 ؋ 100F
POWER-ON
RESET
CLK/DELAY
GENERATOR
CLOCK
OSCILLATOR
GND
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2001






ADM1052 Datasheet, Funktion
ADM1052
GENERAL DESCRIPTION
The ADM1052 is a dual, precision, voltage regulator controller
intended for power rail generation and active bus termination on
personal computer motherboards. It contains a precision 1.2 V
bandgap reference and two channels consisting of control amp-
lifiers driving external power devices. Both channels have an
output of nominally 2.525 V. Each channel has a shutdown
input to turn off amplifier output and protection circuitry for
the external power device.
The ADM1052 operates from a 12 V VCC supply. The output is
disabled until VCC climbs above the reset threshold (6 V–9 V). The
output from the ADM1052 is used to drive external N-channel
MOSFETs, operating as source-followers. This has the advan-
tage that N-channel devices are cheaper than P-channel devices
of similar performance, and the circuit is easier to stabilize than
one using P-channel devices in a common-source configuration.
The external power devices are protected by a “Hiccup Mode”
circuit that operates if the circuit goes out of regulation due to
an output short-circuit. In this case the power device is pulsed
on/off with a 1:40 duty cycle to limit the power dissipation until
the fault condition is removed.
CIRCUIT DESCRIPTION
CONTROL AMPLIFIERS
The reference voltage is amplified and buffered by the control
amplifiers and external MOSFETs, the output voltage of each
channel being determined by the feedback resistor network
between the sense input and the inverting input of the con-
trol amplifier.
A power-on reset circuit disables the amplifier output until VCC
has risen above the reset threshold (6 V–9 V).
Each amplifier output drives the gate of an N-channel power
MOSFET, whose drain is connected to the unregulated supply
input and whose source is the regulated output voltage, which is
also fed back to the appropriate sense input of the ADM1052.
The control amplifiers have high current-drive capability so that
they can quickly charge and discharge the gate capacitance of
the external MOSFET, thus giving good transient response to
changes in load or input voltage.
SHUTDOWN INPUTS
Each channel has a separate shutdown input, which may be
controlled by a logic signal and allows the output of the regula-
tor to be turned on or off. If the shutdown input is held high or
not connected, the regulator operates normally. If the shutdown
input is held low, the enable input of the control amplifier is turned
off and the amplifier output goes low, turning off the regulator.
“HICCUP MODE” FAULT PROTECTION
Hiccup mode fault protection is a simple method of protecting
the external power device without the added cost of external
sense resistors or a current sense pin on the ADM1052. In the
event of a short-circuit condition at the output, the output
voltage will fall. When the output voltage of a channel falls 20%
below the nominal voltage, this is sensed by the hiccup com-
parator and the channel will go into hiccup mode, where the
enable signal to the control amplifier is pulsed on and off with a
1:40 duty cycle.
To prevent the device inadvertently going into hiccup mode
during power-up or during channel enabling, the hiccup mode is
held off for approximately 60 ms on both channels. By this time
the output voltage should have reached its correct value. In the
case of power-up, the hold-off period starts when VCC reaches the
power-on reset threshold of 6 V–9 V. In the case of channel
enabling, the hold-off period starts when SHDN is taken high.
Note that the hold-off timeout applies to both channels even if
only one channel is disabled/enabled.
As the 3.3 V input to the drain of the MOSFET is not moni-
tored, it should ideally rise at the same or a faster rate than VCC.
At the very least it must be available in time for VOUT to reach its
final value before the end of the power-on delay. If the output
voltage is still less than 80% of the correct value after the power-
on delay, the device will go into hiccup mode until the output
voltage exceeds 80% of the correct value during a hiccup mode
on-period. Of course, if there is a fault condition at the output
during power-up, the device will go into hiccup mode after
the power-up delay and remain there until the fault condition
is removed.
The effect of power-on delay is illustrated in Figure 2, which
shows an ADM1052 being powered up with a fault condition.
The output current rises to a very high value during the power-
on delay, the device goes into hiccup mode, and the output is
pulsed on and off at 1:40 duty cycle. When the fault condition is
removed, the output voltage recovers to its normal value at the
end of the hiccup mode off period.
The load current at which the ADM1052 will go into hiccup
mode is determined by three factors:
• The input voltage to the drain of the MOSFET, VIN
• The output voltage VOUT (–20%)
• The on-resistance of the MOSFET, RON
IHICCUP = (VIN (0.8 × VOUT))/RON
It should be emphasized that the hiccup mode is not intended as
a precise current limit but as a simple method of protecting the
external MOSFET against catastrophic fault conditions such as
output short circuits.
–6– REV. A

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