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PDF RC5054A Data sheet ( Hoja de datos )
| Número de pieza | RC5054A | |
| Descripción | Programmable Synchronous DC-DC Converter Controller for Low Voltage Microprocessors | |
| Fabricantes | Fairchild Semiconductor | |
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RC5054A
Programmable Synchronous DC-DC Converter
Controller for Low Voltage Microprocessors
Features
• Drives Two N-Channel MOSFETs
• Operates from +5V Power Input
• Simple Single-Loop Control Design
- Voltage-Mode PWM Control
• Fast Transient Response
- High-Bandwidth Error Amplifier
- Full 0% to 100% Duty Ratio
• Excellent Output Voltage Regulation
• TTL Compatible 5 Bit Digital-to-Analog Output Voltage
Selection
- Wide Range - 1.3VDC to 3.5VDC
- 0.1V Binary Steps from 2.1VDC to 3.5VDC
- 0.05V Binary Steps from 1.3VDC to 2.1VDC
• Power-Good Output Voltage Monitor
• Over-Voltage and Over-Current Fault Monitors
- Does Not Require Extra Current Sensing Element, Uses
MOSFET’s RDS(ON)
• Small Converter Size
- Constant Frequency Operation
- 200kHz Free-Running Oscillator Programmable from
50kHz to 1MHz
Applications
• Power Supply for Pentium®, Pentium Pro, PowerPC™
and Alpha™ Microprocessors
• High-Power 5V to 3.xV DC-DC Regulators
• Low-Voltage Distributed Power Supplies
Description
The RC5054A provides complete control and protection for
a DC-DC converter optimized for high-performance micro-
processor applications. It is designed to drive two N-Channel
MOSFETs in a synchronous-rectified buck topology. The
RC5054A integrates all of the control, output adjustment,
monitoring and protection functions into a single package.
The output voltage of the converter is easily adjusted and
precisely regulated. The RC5054A includes a 5-input digital-
to-analog converter (DAC) that adjusts the output voltage
from 2.1VDC to 3.5VDC in 0.1V increments and from
1.3VDC to 2.1VDC in 0.05V steps.
The RC5054A provides simple, single feedback loop, volt-
Block Diagram
VSEN
OCSET
VID0
VID1
VID2
VID3
VID4
FB
COMP
RT
VCC
REFERENCE
D/A
CONVERTER
(DAC)
110%
90%
115%
200µA
+
-
+
-
OVER-
VOLTAGE
+
-
+
- OVER-
CURRENT
4V
POWER-ON
RESET (POR)
SOFT-
START
10µA
DACOUT
+
-
ERROR
AMP
PWM
COMPARATOR
+
-
INHIBIT
PWM
GATE
CONTROL
LOGIC
OSCILLA TOR
PGOOD
OVP
SS
BOOT
UGATE
PHASE
LGATE
PGND
GND
Rev. 1.0.2
Alpha is a trademark of Digital Equipment Corporation. Pentium is a registered trademark of Intel Corporation. PowerPC is a trademark of IBM
Corporation.
1 page  
PRODUCT SPECIFICATION
RC5054A
Functional Description
Initialization
The RC5054A automatically initializes upon receipt of
power. Special sequencing of the input supplies is not neces-
sary. The Power-On Reset (POR) function continually moni-
tors the input supply voltages. The POR monitors the bias
volt-age at the VCC pin and the input voltage (VIN) on the
OCSET pin. The level on OCSET is equal to VIN less a fixed
voltage drop (see over-current protection). The POR function
initiates soft start operation after both input supply voltages
exceed their POR thresholds. For operation with a single
+12V power source, VIN and VCC are equivalent and the
+12V power source must exceed the rising VCC threshold
before POR initiates operation.
Soft Start
The POR function initiates the soft start sequence. An inter-
nal 10µA current source charges an external capacitor (CSS)
on the SS pin to 4V. Soft start clamps the error amplifier out-
put (COMP pin) and reference input (+ terminal of error
amp) to the SS pin voltage. Figure 1 shows the soft start
interval with CSS = 0.1µF. Initially the clamp on the error
amplifier (COMP pin) controls the converter’s output volt-
age. At t1 in Figure 1, the SS voltage reaches the valley of the
oscillator’s triangle wave. The oscillator’s triangular wave-
form is compared to the ramping error amplifier voltage. This
generates PHASE pulses of increasing width that charge the
output capacitor(s). This interval of increasing pulse width
continues to t2. With sufficient output voltage, the clamp on
the reference input controls the output voltage. This is the
interval between t2 and t3 in Figure 1. At t3 the SS voltage
exceeds the DACOUT voltage and the output voltage is in
regulation. This method provides a rapid and controlled
output voltage rise. The PGOOD signal toggles ‘high’ when
the output voltage (VSEN pin) is within ±5% of DACOUT.
The 2% hysteresis built into the power good comparators
prevents PGOOD oscillation due to nominal output voltage
ripple.
PGOOD
(2V/DIV)
0V
Over-Current Protection
The over-current function protects the converter from a
shorted output by using the upper MOSFET’s on-resistance,
RDS(ON) to monitor the current. This method enhances the
converter’s efficiency and reduces cost by eliminating a current
sensing resistor. The over-current function cycles the soft-
start function in a hiccup mode to provide fault protection. A
resistor (ROCSET) programs the over-current trip level. An
internal 200µA current sink develops a voltage across ROCSET
that is referenced to VIN. When the voltage across the upper
MOSFET (also referenced to VIN) exceeds the voltage across
ROCSET , the over-current function initiates a soft-start
sequence. The soft-start function discharges CSS with a 10µA
current sink and inhibits PWM operation. The soft-start func-
tion recharges CSS, and PWM operation resumes with the
error amplifier clamped to the SS voltage. Should an over-
load occur while recharging CSS, the soft start function
inhibits PWM operation while fully charging CSS to 4V to
complete its cycle. Figure 2 shows this operation with an
overload condition. Note that the inductor current increases
to over 15A during the CSS charging interval and causes an
over-current trip. The converter dissipates very little power
with this method. The measured input power for the condi-
tions of Figure 2 is 2.5W.
The over-current function will trip at a peak inductor current
(IPEAK) determined by:
IPEAK
=
I---O---C----S---E---T----•-----R----O----C---S---E---T--
RDS(ON)
4V
2V
0V
15A
10A
5A
0A
Time (20ms/DIV)
SOFT-START
(1V/DIV)
OUTPUT
VOLTAGE
(1V/DIV)
0V
0V
t1 t2
t3
Time (5ms/DIV)
Figure 1. Soft Start Interval
Figure 2. Over-Current Operation
where IOCSET is the internal OCSET current source (200µA
typical). The OC trip point varies mainly due to the MOSFET’s
RDS(ON) variations. To avoid over-current tripping in the
normal operating load range, find the ROCSET resistor from
the equation above with:
• The maximum RDS(ON) at the highest junction temperature.
• The minimum IOCSET from the specification table.
• Determine IPEAK for IPEAK > IOUT(MAX) + (∆I)/2,
where ∆I is the output inductor ripple current.
5
5 Page 
PRODUCT SPECIFICATION
RC5054A DC-DC Converter
Application Circuit
Figure 10 shows an application circuit of a DC-DC Converter
for an Intel Pentium Pro microprocessor.
RC5054A
VIN = +5V
F1
0.1µF
L1 - 1µH
C1
5x 1000µF
+12V
47Ω
2N6394
2x 1µF
2K
1 µF
SS 3
VSEN 1
VCC
18
OVP
19
MONITOR
AND
PROTECTION
1000pF
2 OCSET
12 PGOOD
15 BOOT
1K
RT
VID0
VID1
VID2
VID3
VID4
FB
20 OSC
4
5
6
7
D/A
8
10
RC5054A
+
-
9
-
+
2.2nF
COMP
8.2nF
20K
14 UGATE 4.7
13 PHASE
17 LGATE 4.7
16 PGND
11
GND
Q1
Q2
0.1µF
1.33K
15
L2
3µH
D1 CO
9x 1000µF
+VO
Component Selection Notes;
C0 - 9 Each 1000µF 6.3W VDC, Sanyo MV-GX or Equivalent
C1 - 5 Each 1000µF 25W VDC, Sanyo MV-GX or Equivalent
L2 - Core: Micrometals T50-52B; Each Winding: 10 Turns of 16AWG
L1 - Core: Micrometals T50-52; Winding: 5 Turns of 18AWG
D1 - 3A, 40V Schottky, Motorola MBR340 or Equivalent
Q1, Q2 - Fairchild FDB6030L
Figure 9. Pentium Pro DC-DC Converter
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet RC5054A.PDF ] | |
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