ISL6430.pdf 데이터시트 (총 12 페이지) - 파일 다운로드 ISL6430 데이타시트 다운로드

No Preview Available !

®
Data Sheet
July 2003
ISL6430
FN9017.2
Single Sync Buck PWM Controller for
Broadband Gateway Applications
The ISL6430 provides complete control and protection for a
DC-DC converter optimized for high-performance broadband
gateway applications. It is designed to drive two N Channel
MOSFETs in a synchronous-rectified buck topology. The
ISL6430 integrates all of the control, output adjustment,
monitoring and protection functions into a single package.
The output voltage of the converter can be precisely
regulated to as low as 1.27V, with a maximum tolerance of
±1% over temperature and line voltage variations.
The ISL6430 provides simple, single feedback loop, voltage-
mode control with fast transient response. It includes a
200kHz free-running triangle-wave oscillator that is
adjustable from below 50kHz to over 1MHz. The error
amplifier features a 15MHz gain-bandwidth product and
6V/µs slew rate which enables high converter bandwidth for
fast transient performance. The resulting PWM duty ratio
ranges from 0% to 100%.
The ISL6430 protects against over-current conditions by
inhibiting PWM operation. The ISL6430 monitors the current
by using the rDS(ON) of the upper MOSFET which eliminates
the need for a current sensing resistor.
Ordering Information
TEMP.
PART NUMBER RANGE (oC)
PACKAGE
PKG. DWG. #
ISL6430CB
0 to 70 14 Ld SOIC
M14.15
ISL6430CR
0 to 70 16 Ld QFN
L16.5x5B
Add -T suffix to either option for tape and reel packaging.
Pinout
ISL6430 (SOIC)
TOP VIEW
RT 1
OCSET 2
SS 3
COMP 4
FB 5
EN 6
GND 7
14 VCC
13 PVCC
12 LGATE
11 PGND
10 BOOT
9 UGATE
8 PHASE
Features
• Drives Two N-Channel MOSFETs
• Operates From +5V or +12V 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
- 1.27V Internal Reference
- ±1% Over Line Voltage and Temperature
• Over-Current Fault Monitor
- Does Not Require Extra Current Sensing Element
- Uses MOSFETs rDS(ON)
• Small Converter Size
- Constant Frequency Operation
- 200kHz Free-Running Oscillator Programmable from
50kHz to Over 1MHz
• 14-Lead SOIC and 16-Lead QFN
Applications
• Cable Modems, Set-Top Boxes and DSL Modems
• DSP and Core Communications Processor Supplies
• High-Power 5V Input DC-DC Regulators
• Low-Voltage Distributed Power Supplies
ISL6430 (QFN)
TOP VIEW
16 15 14 13
NC 1
COMP 2
FP 3
EN 4
12 PVCC
11 LGATE
10 PGND
9 BOOT
5678
1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright © Intersil Americas Inc. 2003. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.

No Preview Available !

ISL6430
Typical Application
12V
VCC
SS MONITOR AND
PROTECTION
RT
OSC
REF
ISL6430
-
FB
++
-
COMP
+5V OR +12V
OCSET
EN
BOOT
UGATE
PHASE
PVCC +12V
LGATE
PGND
GND
+VO
Block Diagram
VCC
OCSET
FB
COMP
RT
200µA
POWER-ON
RESET (POR)
+
- OVER-
CURRENT
4V
SOFT-
START
10µA
1.27 VREF
REFERENCE
+
-
ERROR
AMP
PWM
COMPARATOR
INHIBIT
+
- PWM
GATE
CONTROL
LOGIC
OSCILLATOR
EN
SS
BOOT
UGATE
PHASE
PVCC
LGATE
PGND
GND
2

No Preview Available !

ISL6430
Absolute Maximum Ratings
Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +15.0V
Boot Voltage, VBOOT - VPHASE . . . . . . . . . . . . . . . . . . . . . . +15.0V
Input, Output or I/O Voltage . . . . . . . . . . . . GND -0.3V to VCC +0.3V
ESD Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class 2
Operating Conditions
Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . +12V ±10%
Ambient Temperature Range. . . . . . . . . . . . . . . . . . . . . 0oC to 70oC
Junction Temperature Range . . . . . . . . . . . . . . . . . . . 0oC to 125oC
Thermal Information
Thermal Resistance
θJA (oC/W) θJC (oC/W)
SOIC Package (Note 1) . . . . . . . . . . . .
67
N/A
QFN Package (Note 2). . . . . . . . . . . . .
35
5
Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . 150oC
Maximum Storage Temperature Range . . . . . . . . . -65oC to 150oC
Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300oC
(SOIC Lead tips only)
For Recommended soldering conditions see Tech Brief TB389.
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTE:
1. θJA is measured with the component mounted on a high effective thermal conductivity test board in free air. See Tech Brief TB379 for details.
2. θJA is measured in free air with the component mounted on a high effective thermal conductivity test board with “direct attach” features. θJC, the
“case temp” is measured at the center of the exposed metal pad on the package underside. See Tech Brief TB379.
Electrical Specifications Recommended operating conditions, unless otherwise noted.
PARAMETER
SYMBOL
TEST CONDITIONS
VCC SUPPLY CURRENT
Nominal Supply
Shutdown Supply
ICC EN = VCC; UGATE and LGATE Open
EN = 0V
POWER-ON RESET
Rising VCC Threshold
Falling VCC Threshold
Enable - Input threshold Voltage
Rising VOCSET Threshold
OSCILLATOR
VOCSET = 4.5VDC
VOCSET = 4.5VDC
VOCSET = 4.5VDC
Free Running Frequency
Total Variation
Ramp Amplitude
REFERENCE
VOSC
RT = OPEN, VCC = 12
6k< RT to GND < 200k
RT = OPEN
Reference Voltage
ERROR AMPLIFIER
DC Gain
Gain-Bandwidth Product
GBW
Slew Rate
SR COMP = 10pF
GATE DRIVERS
Upper Gate Source
Upper Gate Sink
Lower Gate Source
Lower Gate Sink
PROTECTION
IUGATE
RUGATE
ILGATE
RLGATE
VBOOT - VPHASE = 12V, VUGATE = 6V
ILGATE = 0.3A
VCC = 12V, VLGATE = 6V
ILGATE = 0.3A
OCSET Current Source
Soft Start Current
IOCSET
ISS
VOCSET = 4.5VDC
MIN TYP MAX UNITS
- 5 - mA
-
50 100
µA
- - 10.4
8.2 -
-
0.8 - 2.0
- 1.27 -
V
V
V
V
185 200 215
kHz
-15 - +15 %
- 1.9 - VP-P
1.258 1.270 1.282
V
- 88 -
dB
- 15 - MHz
- 6 - V/µs
350 500
-
- 5.5 10
300 450
-
- 3.5 6.5
mA
mA
170 200 230
- 10 -
µA
µA
3

No Preview Available !

ISL6430
Typical Performance Curves
1000
100
10
RT PULLUP
TO +12V
RT PULLDOWN
TO VSS
10 100 1000
SWITCHING FREQUENCY (kHz)
FIGURE 1. RT RESISTANCE vs FREQUENCY
Functional Pin Description
RT
This pin provides oscillator switching frequency adjustment.
By placing a resistor (RT) from this pin to GND, the nominal
200kHz switching frequency is increased according to the
following equation:
F
s
200
k
Hz
+
--5---------1---0----6--
RT(kΩ)
(RT to GND)
Conversely, connecting a pull-up resistor (RT) from this pin
to VCC reduces the switching frequency according to the
following equation.:
F
s
200
k
Hz
--4---------1---0----7--
RT(kΩ)
(RT to 12V)
OCSET
Connect a resistor (ROCSET) from this pin to the drain of the
upper MOSFET. ROCSET, an internal 200µA current source
(IOCS), and the upper MOSFET on-resistance (rDS(ON)) set
the converter over-current (OC) trip point according to the
following equation:
IPEAK
=
I--O-----C----S---------R-----O----C-----S---E----T--
rDS(ON)
An over-current trip cycles the soft-start function.
SS
Connect a capacitor from this pin to ground. This capacitor,
along with an internal 10µA current source, sets the soft-
start interval of the converter.
COMP and FB
COMP and FB are the available external pins of the error
amplifier. The FB pin is the inverting input of the error
amplifier and the COMP pin is the error amplifier output.
These pins are used to compensate the voltage-control
feedback loop of the converter.
80
70
60
CGATE = 3300pF
50
40
30 CGATE = 1000pF
20
10 CGATE = 10pF
0
100 200 300 400 500 600 700 800 900 1000
SWITCHING FREQUENCY (kHz)
FIGURE 2. BIAS SUPPLY CURRENT vs FREQUENCY
EN
This pin is the open-collector enable pin. Pull this pin below
1V to disable the converter. In shutdown, the soft start pin is
discharged and the UGATE and LGATE pins are held low.
GND
Signal ground for the IC. All voltage levels are measured
with respect to this pin.
PHASE
Connect the PHASE pin to the upper MOSFET source. This
pin is used to monitor the voltage drop across the MOSFET
for over-current protection. This pin also provides the return
path for the upper gate drive.
UGATE
Connect UGATE to the upper MOSFET gate. This pin
provides the gate drive for the upper MOSFET.
BOOT
This pin provides bias voltage to the upper MOSFET driver.
A bootstrap circuit may be used to create a BOOT voltage
suitable to drive a standard N-Channel MOSFET.
PGND
This is the power ground connection. Tie the lower MOSFET
source to this pin.
LGATE
Connect LGATE to the lower MOSFET gate. This pin
provides the gate drive for the lower MOSFET.
PVCC
Provide a bias supply for the lower gate drive to this pin.
VCC
Provide a 12V bias supply for the chip to this pin.
4

No Preview Available !

ISL6430
Functional Description
Initialization
The ISL6430 automatically initializes upon receipt of power.
Special sequencing of the input supplies is not necessary.
The Power-On Reset (POR) function continually monitors
the input supply voltages and the enable (EN) pin. The POR
monitors the bias voltage 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). With the EN pin held to VCC, 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.
The Power-On Reset (POR) function inhibits operation with
the chip disabled (EN pin low). With both input supplies
above their POR thresholds, transitioning the EN pin high
initiates a soft start interval.
Soft Start
The POR function initiates the soft start sequence. An internal
10µA current source charges an external capacitor (CSS) on
the SS pin to 4V. Soft start clamps the error amplifier output
(COMP pin) and reference input (+ terminal of error amp) to
the SS pin voltage. Figure 3 shows the soft start interval with
CSS = 0.1µF.
SOFT-START
(1V/DIV)
OUTPUT
VOLTAGE
0V (1V/DIV)
0V
t1 t2
t3
TIME (5ms/DIV)
FIGURE 3. SOFT-START INTERVAL
Initially the clamp on the error amplifier (COMP pin) controls
the converter’s output voltage. At t1 in Figure 3, the SS
voltage reaches the valley of the oscillator’s triangle wave.
The oscillator’s triangular waveform 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 3. At t3 the SS voltage exceeds the reference
voltage and the output voltage is in regulation. This method
provides a rapid and controlled output voltage rise.
4V
2V
0V
15A
10A
5A
0A
TIME (20ms/DIV)
FIGURE 4. OVER-CURRENT OPERATION
Over-Current Protection
The over-current function protects the converter from a
shorted output by using the upper MOSFETs 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
(typical) current sink develops a voltage across ROCSET that
is reference 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 function recharges CSS, and PWM operation resumes
with the error amplifier clamped to the SS voltage. Should an
overload occur while recharging CSS, the soft start function
inhibits PWM operation while fully charging CSS to 4V to
complete its cycle. Figure 4 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
conditions of Figure 4 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)
where IOCSET is the internal OCSET current source (200µA
- typical). The OC trip point varies mainly due to the
MOSFETs rDS(ON) variations. To avoid over-current tripping
5