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PDF ISL6522B Data sheet ( Hoja de datos )
| Número de pieza | ISL6522B | |
| Descripción | Buck and Synchronous Rectifier | |
| Fabricantes | Intersil Corporation | |
| Logotipo |  |
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®
Data Sheet
April 4, 2005
ISL6522B
FN9150.1
Buck and Synchronous Rectifier
Pulse-Width Modulator (PWM) Controller
The ISL6522B provides complete control and protection for a
DC-DC converter optimized for high-performance
microprocessor applications. It is designed to drive two
N-Channel MOSFETs in a synchronous rectified buck topology.
The ISL6522B 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 0.8V, with a maximum tolerance of
±1% over temperature and line voltage variations.
The ISL6522B 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 perform-
ance. The resulting PWM duty ratio ranges from 0-100%.
The ISL6522B protects against overcurrent conditions by
inhibiting PWM operation. The ISL6522B monitors the
current by using the rDS(ON) of the upper MOSFET which
eliminates the need for a current sensing resistor.
Pinouts
ISL6522B (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
ISL6522B (QFN)
TOP VIEW
16 15 14 13
SS 1
COMP 2
FB 3
EN 4
12 PVCC
11 LGATE
10 PGND
9 BOOT
5678
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 0–100% duty ratio
• Excellent output voltage regulation
- 0.8V internal reference
- ±1% over line voltage and temperature
• Overcurrent fault monitor
- Does not require extra current sensing element
- Uses MOSFETs rDS(ON)
• Converter can source and sink current
• Pre-Biased Load Start Up
• Small converter size
- Constant frequency operation
- 200kHz free-running oscillator programmable from
50kHz to over 1MHz
• 14-lead SOIC package and 16-lead 5x5mm QFN Package
• QFN Package
- Compliant to JEDEC PUB95 MO-220 QFN-Quad Flat
No Leads-Product Outline
- Near Chip-Scale Package Footprint; Improves PCB
Efficiency and Thinner in Profile
• Pb-Free Available (RoHS Compliant)
Applications
• Power supply for Pentium®, Pentium Pro, PowerPC® and
AlphaPC™ microprocessors
• FPGA Core DC/DC Converters
• Low-voltage distributed power supplies
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. 2004, 2005. All Rights Reserved. All other trademarks mentioned are the property of their respective owners.
PowerPC® is a trademark of IBM. AlphaPC™ is a trademark of Digital Equipment Corporation. Pentium® is a registered trademark of Intel Corporation.
1 page  
ISL6522B
Electrical Specifications
PARAMETER
Soft START
Soft-Start Current
Peak Soft Start Voltage
GATE DRIVERS
Upper Gate Source
Upper Gate Sink
Lower Gate Source
Lower Gate Sink
PROTECTION
OCSET Current Source
Recommended Operating Conditions, Unless Otherwise Noted (Continued)
SYMBOL
TEST CONDITIONS
MIN TYP
MAX
UNITS
ISS
VSS
IUGATE
RUGATE
ILGATE
RLGATE
VBOOT - VPHASE = 12V, VUGATE = 6V
ISL6522BC, IUGATE = 0.3A
ISL6522BI, IUGATE = 0.3A
VCC = 12V, VLGATE = 6V
ISL6522BC, ILGATE = 0.3A
ISL6522BI, ILGATE = 0.3A
IOCSET VOCSET = 4.5VDC
- 10 -
- 4.5 -
µA
V
350 500
-
- 5.0 8.75
- 5.0 9.25
300 450
-
- 3.2 5.55
- 3.2 5.85
mA
Ω
Ω
mA
Ω
Ω
170 200 230
µA
Typical Performance Curves
1000
100
10
RT PULLUP
TO +12V
RT PULLDOWN
TO VSS
10 100
SWITCHING FREQUENCY (kHz)
FIGURE 1. RT RESISTANCE vs FREQUENCY
1000
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
5
5 Page 
ISL6522B
The response time to a transient is different for the
application of load and the removal of load. The following
equations give the approximate response time interval for
application and removal of a transient load:
tRISE = -VL---O-I--N---×--–---I-V-T---R-O---A-U---N-T--
tFALL = L----O----V--×--O--I--T-U---R-T---A----N--
where: ITRAN is the transient load current step, tRISE is the
response time to the application of load, and tFALL is the
response time to the removal of load. With a +5V input
source, the worst case response time can be either at the
application or removal of load and dependent upon the
output voltage setting. Be sure to check both of these
equations at the minimum and maximum output levels for
the worst case response time.
Input Capacitor Selection
Use a mix of input bypass capacitors to control the voltage
overshoot across the MOSFETs. Use small ceramic
capacitors for high frequency decoupling and bulk capacitors
to supply the current needed each time Q1 turns on. Place
the small ceramic capacitors physically close to the
MOSFETs and between the drain of Q1 and the source of Q2.
The important parameters for the bulk input capacitor are the
voltage rating and the RMS current rating. For reliable
operation, select the bulk capacitor with voltage and current
ratings above the maximum input voltage and largest RMS
current required by the circuit. The capacitor voltage rating
should be at least 1.25 times greater than the maximum
input voltage and a voltage rating of 1.5 times is a
conservative guideline. The RMS current rating requirement
for the input capacitor of a buck regulator is approximately
1/2 the DC load current.
For a through-hole design, several electrolytic capacitors
(Panasonic HFQ series or Nichicon PL series or Sanyo
MV-GX or equivalent) may be needed. For surface mount
designs, solid tantalum capacitors can be used, but caution
must be exercised with regard to the capacitor surge current
rating. These capacitors must be capable of handling the
surge-current at power-up. The TPS series available from
AVX, and the 593D series from Sprague are both surge
current tested.
MOSFET Selection/Considerations
The ISL6522B requires two N-Channel power MOSFETs.
These should be selected based upon rDS(ON), gate supply
requirements, and thermal management requirements.
In high-current applications, the MOSFET power dissipation,
package selection and heatsink are the dominant design
factors. The power dissipation includes two loss
components; conduction loss and switching loss. The
conduction losses are the largest component of power
dissipation for both the upper and the lower MOSFETs.
These losses are distributed between the two MOSFETs
according to duty factor. The switching losses seen when
sourcing current will be different from the switching losses seen
when sinking current. When sourcing current, the upper
MOSFET realizes most of the switching losses. The lower
switch realizes most of the switching losses when the converter
is sinking current (see the equations below).
Losses while Sourcing Current
PUPPER
=
Io2
×
rD
S
(
O
N
)
×
D
+
1--
2
⋅
I
o
×
VI
N
×
tS
W
×
FS
PLOWER = Io2 x rDS(ON) x (1 - D)
Losses while Sinking Current
PUPPER = Io2 x rDS(ON) x D
PLOWER
=
Io2
×
rDS(ON)
×
(1
–
D)
+
1--
2
⋅
Io
×
VIN
×
tSW
×
FS
Where: D is the duty cycle = VOUT / VIN,
tSW is the switching interval, and
FS is the switching frequency.
These equations assume linear voltage-current transitions
and do not adequately model power loss due the reverse-
recovery of the upper and lower MOSFET’s body diode. The
gate-charge losses are dissipated by the ISL6522B and do
not heat the MOSFETs. However, large gate-charge
increases the switching interval, tSW which increases the
upper MOSFET switching losses. Ensure that both
MOSFETs are within their maximum junction temperature at
high ambient temperature by calculating the temperature
rise according to package thermal-resistance specifications.
A separate heatsink may be necessary depending upon
MOSFET power, package type, ambient temperature and air
flow.
Standard-gate MOSFETs are normally recommended for
use with the ISL6522B. However, logic-level gate MOSFETs
can be used under special circumstances. The input voltage,
upper gate drive level, and the MOSFETs absolute gate-to-
source voltage rating determine whether logic-level
MOSFETs are appropriate.
Figure 9 shows the upper gate drive (BOOT pin) supplied by
a bootstrap circuit from VCC . The boot capacitor, CBOOT
develops a floating supply voltage referenced to the PHASE
pin. This supply is refreshed each cycle to a voltage of VCC
less the boot diode drop (VD) when the lower MOSFET, Q2
turns on. A logic-level MOSFET can only be used for Q1 if
the MOSFETs absolute gate-to-source voltage rating
exceeds the maximum voltage applied to VCC. For Q2, a
logic-level MOSFET can be used if its absolute gate-to-
source voltage rating exceeds the maximum voltage applied
to PVCC.
11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet ISL6522B.PDF ] | |
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