an1200

ISL88550AEVAL1Z Kit: Synchronous Step Down
Controller with Sourcing and Sinking LDO Regulator
®
Application Note
July 23, 2008
General Description
Features
ISL88550A integrates a synchronous buck PWM controller
to generate VDDQ, a sourcing and sinking LDO linear
regulator to generate VTT, and a 10mA reference output
buffer to generate VTTR. The buck controller drives two
external N-Channel MOSFETs to generate output voltages
down to 0.7V from a 2V to 25V input with output currents up
to 15A. The LDO can sink or source up to1.5A continuous
and 2.5A peak current with fast response. Both the LDO
output and the 10mA reference buffer output can be made to
track the REFIN voltage via a built-in resistive divider. These
features make the ISL88550A ideally suited for DDR
memory applications in desktops, notebooks and graphic
cards.
Buck Controller
The PWM controller in the ISL88550A uses constant-on-time
PWM architecture with a programmable switching frequency
of up to 600kHz. This control scheme handles wide
input/output voltage ratios with ease and provides 100ns
“instant-on” response to load transients while maintaining
high efficiency and a relatively constant switching frequency.
The ISL88550A offers full programmable UVP/OVP and skip
mode options ideal in portable applications. Skip mode
allows for improved efficiency at lighter loads.
The VTT and VTTR outputs track to within 1% of VREFIN/2.
The high bandwidth of this LDO regulator allows excellent
transient response without the need for bulk capacitors, thus
reducing the cost and size.
AN1200.3
• Constant-On PWM with 100ns Load-Step Response
• Up to 95% Efficiency
• 2V to 25V Input Voltage Range
• 1.8V/2.5V fixed or 0.7V to 3.5V Adjustable Output
• 200kHz, 300kHz, 450kHz, 600kHz Switching Frequencies
• Programmable Current Limit with Foldback Capability
• 1.7ms Digital Soft-Start and Independent Shutdown
• Overvoltage/Undervoltage Protection Option
• Power-Good Window Comparator
LDO Section
• Fully Integrated VTT and VTTR Capability
• VTT has ±2.5A Sourcing/Sinking Capability
• VTT and VTTR Outputs Track VREFIN/2
• VTT and VTTR within 1% of VREFIN/2
• All Ceramic Output Capacitor Designs
• 1.0V to 2.8V Input REFIN Range
• Analog Soft-Start Option and Independent Shutdown
• Power-Good Window Comparator
Applications
Pinout
• DDR I and DDR II Memory Power Supplies
ISL88550A
(28 LD TQFN)
TOP VIEW
• Desktop Computers
TPO
SHDNA#
AVDD
SKIP#
GND
PGND1
VDD
• Notebooks and Desknotes
28
27
26
25
24
23
22
• Graphics Cards
• Game Consoles
BOOT
REF
3
19
PHASE
ILIM
4
18
UGATE
POK1
5
17
VIN
POK2
6
16
OUT
STBY#
7
15
FB
8
9
10
11
12
13
14
REFIN
20
VTTI
2
VTT
OVP/UVP
PGND2
LGATE
VTTR
21
VTTS
1
SS
TON
1
• Networking and RAID
Ordering Information
PART
PACKAGE
ISL88550AEVAL1Z Evaluation Board
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2006, 2008. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
Application Note 1200
What’s Inside
TABLE 1. SWITCH 1 SETTINGS
The Evaluation Board Kit contains the following materials:
SW1
SKIP
OPERATING MODE
1
Connect to GND
Normal operation mode, allow
automatic PWM/PFM switchover for
pulse-skipping at light load.
• ISL88550AEVAL1Z Kit (this document)
2
Connect to AVDD
Low noise, fixed-frequency PWM
mode.
Recommended Equipment
3
No Connection
NA
• The ISL88550AEVAL1Z REVA board
• The ISL88550A data sheet
The following materials are recommended to perform
testing:
NOTE: Only toggle one position at a time
• 0V to 22V power supply with at least 15A source current
capability, battery, notebook AC-adapter
TABLE 2. SWITCH 2 SETTINGS
SW2
• 5V Bias supply for VDD
• Two electronic loads capable of sinking current up to 15A
• Dummy loads for the LDO’s
SHDNA#
1
Connect to GND
Shutdown mode. VDDQ, VTTR,
and VTT output.
2
Connect to AVDD
Enable ISL88550. Rising edge
clear the fault protection. Connect
to AVDD for normal operation.
3
No Connection
NA
• Digital multimeters (DMMs)
• 100MHz quad-trace oscilloscope
• Signal generator
SHUTDOWN CONTROL
NOTE: Only toggle one position at a time
Quick Setup Guide
1. Ensure that the circuit is correctly connected to the supply
and loads prior to applying any power.
2. Connect the bias supply to VDD, the + terminal to P3
(VDD) and - return to TP5 (AGND).
3. Verify that position 2’s are ON for SW1, SW2, SW3, and
SW5. Verify that position 1 is ON for SW4. Make sure that
no other switch position is ON at the same time.
4. Turn on the VIN power supply.
TABLE 3. SWITCH 3 SETTINGS
SW3
tON
tON ON-TIME SELECTION
1
Connect to GND.
tON set to 600kHz frequency
2
Connect to AVDD.
tON set to 200kHz frequency
3
Connect to REF.
tON set to 450kHz frequency
-
OPEN
tON set to 300kHz frequency
NOTE: Only toggle one position at a time
5. Turn on 5V bias supply.
6. Verify the outputs voltages are 1.8V for VDDQ and 0.9V
for VTT.
Evaluating the Other Output Voltage
TABLE 4. SWITCH 4 SETTINGS
SW4
The ISL88550EVAL1Z kit outputs are preset to 1.8V and
0.9V; however, VDDQ output voltage can be adjusted from
0.8V to 3.5V by using Equation 1:
OVP/UVP
FAULT PROTECTION CONTROL
Descriptor
R 10 = ( R 8 ⁄ [ ( VOUT/VFB ) – 1 ] )
(EQ. 1)
Set R8 to 25kΩ; and VFB to 0.7V
1
Connect to GND
Disable OVP and UVP
2
Connect to AVDD
Enable OVP and UVP
3
Connect to REF
Disable OVP and enable UVP
-
OPEN
Enable OVP and disable UVP
NOTE: Only toggle one position at a time
VDDQ output can also be set to 2.5V by shorting FB pin to
GND with R10.
VTT output voltage is half on VDDQ in DDR application.
VTTI can be powered directly from VDDQ. For better
efficiency, VTTI can be powered from an external power
supply. Make sure that R13 is removed.
TABLE 5. SWITCH 5 SETTINGS
SW5
STBY#
FAULT PROTECTION CONTROL
1
Connect to GND
Shutdown VTT in high impedance
state. VTTR is still active.
2
Connect to VCC
Enable VTT
3
No Connection
NOTE: Only toggle one position at a time
2
AN1200.3
July 23, 2008
ISL88550AEVAL1Z Schematic DDR II
P3
R5
10
TP5
1
2
1
R1
0
ILIM
UGATE
18
POK1
VIN
17
OUT
16
EP
C16
10UF
IRF7821
1
2
TP1 4
L1
1UH
Q2
VIN
1
8
2
7
3
6
4
5
15
FB
STBY
R6
0
C14
10UF
FB
C18
OPEN
IRF7832
VDDQ
1
D4
R25
OPEN
TP2
4
C27
C29
C22
22UF 220UF 220UF
C15
OPEN
DNP
C24
0.1UF
1
R14
0
TP4
VTTI
1
C9
10UF
TP3
P15
1
4
R13
0
P14 1
VTT
P16
2
C3
10UF
C7
OPEN
R2
0
FB
R10
1
C12
10UF
C23
0.1UF
C13
10UF
AVDD
REF
6
5
4
6
5
4
6
5
4
6
5
4
6
5
4
R12
20K
REF
R4
100K
TP11
1
1
2
3
1
2
3
1
2
3
S4
SKIP#
SHDNA#
TON
S5
OVP/UVP
POK1
1
2
3
S3
S2
1
2
3
S1
STBY#
15.8K
C6
1UF
C5
10UF
R11
100K
TP10
1
POK2
10.0K
C2
10UF
3
C8
3300PF
R8
1
P7
1
2
3
ISL88550CR
5
1
POK2
4
VIN
3
PHASE
19 0
U1
C10
0.22UF
R3
8
9
10
11
12
13
14
29
20
6
2
R9
56.2K
POK1 5
POK2 6
STBY# 7
21
BOOT
7
3
P8
Application Note 1200
C1
0.22UF
C17
470PF
LGATE
8
2
1
R15
200K
OVP/UVP
REF
Q1
1
1
4
TON
SS
VTTS
VTTR
PGND2
VTT
VTTI
REFIN
TON
1
OVP/UVP 2
REF 3
DNP
2
3
R16
182K
VDDQ
D3
NC
SHDNA
AVDD
SKIP
GND
PGND1
VDD
1
P2
C11
4.7UF
2
C4
1UF
3
VIN
28
27
SHDNA#
26
25 SKIP#
24
23
22
1
P1
VDD
1
AVDD
AN1200.3
July 23, 2008
Application Note 1200
TABLE 6. COMPONENT LIST
REF DES
QTY
VALUE
TOL.
VOLTAGE
PACKAGE
PART NUMBER
MANUFACTURER
DESCRIPTION
C1, C10
2
0.22µF
10%
50V
SM0805
-
AVX, Samsung, TDK, Murata Multilayer Capacitor
C2, C3, C9
3
10µF
10%
>6.3V
SMD0805
-
AVX, Samsung, TDK, Murata Multilayer Capacitor
C14, C16
2
10µF
10%
25V
SMD1812
-
AVX, Samsung, TDK, Murata X5R Capacitor
C4, C6
2
1µF
10%
10V
SM0805
-
AVX, Samsung, TDK, Murata Multilayer Capacitor
C11
1
4.7µF
10%
10V
SM0805
-
AVX, Samsung, TDK, Murata Multilayer Capacitor
C27
0
OPEN
20%
10V
SMD1210
-
AVX, Samsung, TDK, Murata C Series Capacitor
(EIA:CC1210)
C29, C29
2
220µF
20%
4.0V
EIA_CASE_D
EEFUE0G221R
C17
1
470pF
10%
50V
SM0805
-
AVX, Samsung, TDK, Murata Multilayer Capacitor
C24
1
0.1µF
10%
50V
SM0805
-
AVX, Samsung, TDK, Murata Multilayer Capacitor
C5, C7, C8,
C12, C13,
C15, C18,
C23
0
Open
10%
50V
SM0805/
SM1206
-
AVX, Samsung, TDK, Murata Multilayer Capacitor
D3
0
Open
-
30V
SOT23
BAT54WT1
D4
1
-
3A
40V
SMA
B340LA
L1
1
1.0µH
20%
2mΩ
13_5x13_5
SD10L1
HM65-H1R0
C6125-1R0
FDA1254-1R0M
Q1
1
-
11A
30V
SOIC8
Q2
1
-
16A
30V
R1, R2, R3,
R6, R13,
R14
8
0
1%
R12
1
20k
R9
1
R4, R11
Panasonic
AL POLYMER
On-Semi
30V Schottky
Barrier Diode
Diodes-Inc
3A Low VF
Schottky Barrier
Falco
BI
Sumida
Toko
Shielded SMD
Inductor
IRF7821V
IR
30V 8.3A N-Power
MOSFET
SOIC8
IRF7811AV
IR
30V 10.8A N-Power
MOSFET
150V
0805
-
Generic
Thick Film Chip
Resistor
1%
150V
0805
-
Generic
Thick Film Chip
Resistor
56.2k
1%
150V
0805
-
Generic
Thick Film Chip
Resistor
2
100k
1%
150V
0805
-
Generic
Thick Film Chip
Resistor
R16
1
182k
1%
150V
0805
-
Generic
Thick Film Chip
Resistor
R15
1
200k
1%
150V
0805
-
Generic
Thick Film Chip
Resistor
R5, R25
0
Open
1%
150V
0805/1206
-
Generic
Thick Film Chip
Resistor
R8
1
15.8k
1%
150V
0805
-
Generic
Thick Film Chip
Resistor
R10
1
10k
150V
0805
-
Generic
Thick Film Chip
Resistor
SW1-SW5
5
-
-
-
DIP06
DIP06-SW03
Grayhill
Dip Switch SPST
U1
1
-
-
-
TQFN
ISL88550A
Intersil
High Efficiency
Output Rectifier
Controller
4
AN1200.3
July 23, 2008
Application Note 1200
ISL88550AEVAL1Z Board Layout
FIGURE 1. TOP COMPONENTS
FIGURE 2. TOP LAYER ETCH
5
AN1200.3
July 23, 2008
Application Note 1200
ISL88550AEVAL1Z Board Layout
(Continued)
FIGURE 3. 2ND LAYER ETCH
FIGURE 4. 3RD LAYER ETCH
6
AN1200.3
July 23, 2008
Application Note 1200
ISL88550AEVAL1Z Board Layout
(Continued)
FIGURE 5. BOTTOM LAYER COMPONENTS (MIRRORED)
FIGURE 6. BOTTOM LAYER ETCH (MIRRORED)
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to
verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
7
AN1200.3
July 23, 2008
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