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PDF CS5157 Data sheet ( Hoja de datos )
| Número de pieza | CS5157 | |
| Descripción | CPU 5-Bit Synchronous Buck Controller | |
| Fabricantes | Cherry Semiconductor Corporation | |
| Logotipo |  |
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CS5157
CPU 5-Bit Synchronous Buck Controller
Description
Features
The CS5157 is a 5-bit synchronous
dual N-Channel buck controller. It
is designed to provide unprece-
dented transient response for
today’s demanding high-density,
high-speed logic. The regulator
operates using a proprietary control
method, which allows a 100ns
response time to load transients.
The CS5157 is designed to operate
over a 4.25-16V range (VCC) using
12V to power the IC and 5V as the
main supply for conversion.
The CS5157 is specifically designed
to power Pentium® II processors
and other high performance core
logic. It includes the following fea-
tures: on board, 5-bit DAC, short
circuit protection, 1.0% output tol-
erance, VCC monitor, and pro-
grammable soft start capability. The
CS5157 is available in 16 pin surface
mount.
Application Diagram
Switching Power Supply for core logic - Pentium® II processor
12V 5V
s Dual N-Channel Design
s Excess of 1MHz Operation
s 100ns Transient Response
s 5-Bit DAC
s Backward Compatible with
Adjustable CS5120/5121
s 30ns Gate Rise/Fall Times
s 1% DAC Accuracy
s 5V & 12V Operation
s Remote Sense
s Programmable Soft Start
s Lossless Short Circuit
Protection
s VCC Monitor
s 25ns FET Nonoverlap Time
s V2TM Control Topology
s Current Sharing
s Overvoltage Protection
0.1µF
VID0
VID1
VID2
VID3
VID4
330pF
VCC1 VCC2 VGATE(H)
VID0
VID1
VID2
VID3
VID4
CS5157
VGATE(L)
COFF
PGnd
0.1µF
SS
COMP
0.33µF
LGnd
VFB
VFFB
3.3k
100pF
V2 is a trademark of Switch Power, Inc.
Pentium is a registered trademark of Intel Corporation.
Rev. 12/31/98
1200µF/10V x 3
AlEl
IRL3103
2µH
1.3V to 3.5V @ 13A
IRL3103
1200µF/10V x 5
AlEl
Package Options
16 Lead SO Narrow
VID0 1
VID1
VID2
VID3
SS
VID4
COFF
VFFB
VFB
COMP
LGnd
VCC1
VGATE(L)
PGnd
VGATE(H)
VCC2
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: [email protected]
Web Site: www.cherry-semi.com
1 A ® Company
1 page  
PACKAGE PIN #
16L SO Narrow
11
12
13
14
15
16
Package Pin Description: continued
PIN SYMBOL
FUNCTION
PGnd
VGATE(L)
VCC1
LGnd
COMP
VFB
High current ground for the IC. The MOSFET drivers are referenced to
this pin. Input capacitor ground and the source of lower FET should be
tied to this pin.
Low FET driver pin capable of 1.5A peak switching current.
Input power for the IC and low side gate driver.
Signal ground for the IC. All control circuits are referenced to this pin.
Error amplifier compensation pin. A capacitor to ground should be
provided externally to compensate the amplifier.
Error amplifier DC feedback input. This is the master voltage feedback
which sets the output voltage. This pin can be connected directly to the
output or a remote sense trace.
Block Diagram
VCC1
SS
VID0
VID1
VID2
VID3
VID4
VFB
COMP
VFFB
LGnd
VCC1 Monitor
Comparator
-
+
3.90V
3.85V
5V
60µA
2µA
5 BIT
DAC
Error
+ Amplifier
-
Slow Feedback
PWM
Comparator
-
+
Fast Feedback
-
+
VFFB Low
1V Comparator
PWM
COMP
2.5V
SS Low
- Comparator
+
0.7V
SS High
+ Comparator
-
Maximum
On-Time
Timeout
Normal
Off-Time
Timeout
Extended
Off-Time
Timeout
FAULT
RQ
S Q FAULT
FAULT
Latch
VCC2
VGATE(H)
PGnd
VCC1
VGATE(L)
PGnd
RQ
SQ
PWM
Latch
Off-Time
Timeout
GATE(H) = ON
GATE(H) = OFF
COFF
One Shot
R
SQ
COFF
Time Out
Timer
(30µs)
Edge Triggered
5
5 Page 
Applications Information: continued
used as the source for the regulator output current, the fol-
lowing gate drive is provided;
VGATE(H) = 12V - 5V = 7V, VGATE(L) = 12V (see Figure 17). where:
COFF
=
Period × (1 - duty cycle)
4848.5
,
Period =
1
switching frequency
Trace 3 = VGATE(H) (10V/div.)
Math 1= VGATE(H) - 5VIN
Trace 4 = VGATE(L) (10V/div.)
Trace 2 = Inductor Switching Node (5V/div.)
Figure 17: CS5157 gate drive waveforms depicting rail to rail swing.
The most important aspect of MOSFET performance is
RDSON, which effects regulator efficiency and MOSFET
thermal management requirements.
The power dissipated by the MOSFETs may be estimated
as follows;
Switching MOSFET:
Power = ILOAD2 × RDSON × duty cycle
Synchronous MOSFET:
Power = ILOAD2 × RDSON × (1 - duty cycle)
Duty Cycle =
VOUT + (ILOAD × RDSON OF SYNCH FET)
VIN + (ILOAD × RDSON OF SYNCH FET) - (ILOAD × RDSON OF SWITCH FET)
Off Time Capacitor (COFF)
The COFF timing capacitor sets the regulator off time:
TOFF = COFF × 4848.5
When the VFFB pin is less than 1V, the current charging the
COFF capacitor is reduced. The extended off time can be cal-
culated as follows:
TOFF = COFF × 24,242.5.
Off time will be determined by either the TOFF time, or the
time out timer, whichever is longer.
The preceding equations for duty cycle can also be used to
calculate the regulator switching frequency and select the
COFF timing capacitor:
Schottky Diode for Synchronous MOSFET
A Schottky diode may be placed in parallel with the syn-
chronous MOSFET to conduct the inductor current upon
turn off of the switching MOSFET to improve efficiency.
The CS5157 reference circuit does not use this device due to
it’s excellent design. Instead, the body diode of the syn-
chronous MOSFET is utilized to reduce cost and conducts
the inductor current. For a design operating at 200kHz or so,
the low non-overlap time combined with Schottky forward
recovery time may make the benefits of this device not
worth the additional expense (see Figure 6, channel 2). The
power dissipation in the synchronous MOSFET due to body
diode conduction can be estimated by the following equation:
Power = Vbd × ILOAD × conduction time × switching frequency
Where Vbd = the forward drop of the MOSFET body diode.
For the CS5157 demonstration board as shown in Figure 6;
Power = 1.6V × 13A × 100ns × 233kHz = 0.48W
This is only 1.3% of the 36.4W being delivered to the load.
Input and Output Capacitors
These components must be selected and placed carefully to
yield optimal results. Capacitors should be chosen to pro-
vide acceptable ripple on the input supply lines and regula-
tor output voltage. Key specifications for input capacitors
are their ripple rating, while ESR is important for output
capacitors. For best transient response, a combination of
low value/high frequency and bulk capacitors placed close
to the load will be required.
Output Inductor
The inductor should be selected based on its inductance,
current capability, and DC resistance. Increasing the induc-
tor value will decrease output voltage ripple, but degrade
transient response.
Thermal Management
Thermal Considerations for Power MOSFETs and Diodes
In order to maintain good reliability, the junction tempera-
ture of the semiconductor components should be kept to a
maximum of 150°C or lower. The thermal impedance (junc-
tion to ambient) required to meet this requirement can be
calculated as follows:
Thermal Impedance =
TJUNCTION(MAX) - TAMBIENT
Power
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet CS5157.PDF ] | |
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