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19-1268; Rev 1; 3/98
MAX1636 CPU Supply Evaluation Kit
General Description
The MAX1636 CPU supply evaluation kit (EV kit) circuit
is intended for converting high-voltage battery power
into a low-voltage supply rail for next-generation note-
book CPU cores. The output is digitally adjustable
between 1.25V and 2V, in 50mV increments. The input
range is +7V to +22V. It delivers up to 7A output current
with greater than 87% efficiency. The MAX1636 features
±1% DC output accuracy over all conditions of line,
load, and temperature. The fully assembled and tested
EV kit has excellent dynamic response to correct for fast
load transients.
This EV kit is very specific to notebook CPU core power
supplies, and includes a digital-to-analog converter
(DAC), op-amp buffer, and other high-performance
components tailored to this demanding application.
However, the MAX1636 is a general-purpose, stand-
alone device that can be used without the DAC; see the
MAX1636 data sheet for standard application circuits.
____________________________Features
o
+7V to +22V Input Voltage Range
o
Digitally Adjustable 1.25V to 2V Output Voltage
o
7A Output Current Capability
o
±1% DC Output Accuracy
o
Efficiency = 87%, V
IN
= 7V, V
OUT
= 1.7V
(at I
OUT
= 3A)
o
Fast MOSFETs for Low Switching Losses
o
Tight PC Board Layout for Low Switching Losses
o
Power-Good Output
o
300kHz Switching Frequency
o
Overvoltage and Undervoltage Protection
o
Surface-Mount Construction
o
Fully Assembled and Tested
Evaluates: MAX1636
Ordering Information
PART
MAX1636CPUEVKIT
TEMP. RANGE
0°C to +70°C
IC PACKAGE
20 SSOP
Component List
DESIGNATION QTY
C1, C2, C3,
C4
C5, C7, C8,
C9, C10
C11
C12
C13
C14, C15,
C16
C14, C15,
C16, C17
C18
D1
DESCRIPTION
10µF, 25V ceramic capacitors
Tokin C34Y5U1E106Z or
United Chemicon/Marcon
THCR50E1E106ZT
0.1µF ceramic capacitors
1500pF ceramic capacitor
1µF ceramic capacitor
4.7µF, 16V tantalum capacitor
Sprague 595D475X0016A2B
470µF, 6.3V, 30mΩ low-ESR
tantalum capacitors
Kemet T510X477(1) 006AS
or
470µF, 4V,
470µF, 4V, low-ESR tantalum caps
low-ESR tantalum capacitors
Sprague 594D477X0004R2T
Sprague 594D477X0004R2T
Open
Schottky diode
SGS-Thomson STPS2L25U,
International Rectifier 10BQ040, or
Motorola MBRS130LT3
Schottky diode
Central Semiconductor CMPSH-3
N2
1
DESIGNATION QTY
DESCRIPTION
2.2µH power inductor
Panasonic P1F2R0HL,
Coiltronics UP4-2R2, or
Coilcraft DO5022P-222HC
N-channel MOSFET
Fairchild FDS9412,
International Rectifier IRF7803, or
Siliconix Si9804DY
N-channel MOSFET
Fairchild FDS6680,
International Rectifier IRF7801, or
Siliconix Si4420DY
0.010Ω, 1%, 1W resistor
Dale WSL-2512-R010F
10kΩ, 0.1% resistor
Dale TNPW-1206 series
110kΩ, 0.1% resistor
Dale TNPW-1206 series
13.7kΩ, 0.1% resistor
Dale TNPW-1206 series
51Ω, 5% resistor
100kΩ, 5% resistor
4
L1
1
5
1
1
1
N1
1
3
R1
R2
R3
R4
R5
R6
1
1
1
1
1
1
4
0
1
D2
1
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
For small orders, phone 408-737-7600 ext. 3468.
MAX1636 CPU Supply Evaluation Kit
Evaluates: MAX1636
Component List (continued)
DESIGNATION
R7
R8–R12, R14, R15, R16
SW1
U1
U2
U3
None
None
JU3, JU4, JU5
QTY
1
8
1
1
1
1
1
1
3
DESCRIPTION
20Ω, 5% resistor
1MΩ, 5% resistors
Four-position dip switch
MAX1636EAP (20-pin SSOP)
MAX5480BEEE (16-pin QSOP)
MAX4332ESA (8-pin SO) or
MAX4163ESA (alternate type
with lower supply current but
slightly degraded accuracy)
MAX1636 PC board
MAX1636 data sheet
2-pin header
_________________________Quick Start
The MAX1636 EV kit is fully assembled and tested.
Follow these steps to verify board operation.
Do not
turn on the power supply until all connections are
completed.
1) Connect a +7V to +22V supply voltage to the VIN
pad. Connect ground to the GND pad.
2) Connect a voltmeter and load, if any, to the VOUT
pad.
3) Turn on the power supply to the board. Verify that
the output voltage is 2V (SW1 set to all zeros).
4) Set switch SW1 per Table 1 to get the desired out-
put voltage. Input power may need to be cycled off
and on for new voltage settings to take effect.
Table 1. Output Voltage Settings
Component Supplier
SUPPLIER
AVX
Central
Semiconductor
Coilcraft
Dale-Vishay
Fairchild
International
Rectifier
IRC
Kemet
Motorola
Panasonic
Sanyo
SGS-Thomson
Siliconix
Sprague
Sumida
Tokin
Vishay/Vitramon
PHONE
(803) 946-0690
(516) 435-1110
(847) 639-6400
(402) 564-3131
(408) 721-2181
(310) 322-3331
(512) 992-7900
(864) 963-6300
(602) 303-5454
(201) 348-7522
(619) 661-6835
(617) 259-0300
(408) 988-8000
(603) 224-1961
(847) 956-0666
(408) 432-8020
(203) 268-6261
FAX
(803) 626-3123
(516) 435-1824
(847) 639-1469
(402) 563-6418
(408) 721-1635
(310) 322-3332
(512) 992-3377
(864) 963-6521
(602) 994-6430
(201) 392-4441
(619) 661-1055
(617) 259-9442
(408) 970-3950
(603) 224-1430
(847) 956-0702
(408) 434-0375
(203) 452-5670
D3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
D2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
D1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
D0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
V
OUT
(V)
2.00
1.95
1.90
1.85
1.80
1.75
1.70
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.25
Note:
Please indicate that you are using the MAX1636 when
contacting these component suppliers.
2
_______________________________________________________________________________________
MAX1636 CPU Supply Evaluation Kit
_______________Detailed Description
The MAX1636 EV kit provides a digitally adjustable out-
put voltage between 1.25V and 2V from a +7V to +22V
input supply. The output voltage is digitally adjusted by
the MAX5480, a multiplying DAC, which sums a vari-
able output current into the FB feedback node. This
DAC operates in voltage-output mode and relies on the
precise MAX1636 REF output to generate an accurate
reference current. The DAC has buffer amplifiers on the
input and output to prevent the R2R ladder in the
MAX5480 from excessively loading the reference or
interacting with the normal FB resistor-divider imped-
ance. The buffered DAC output swings 0V to REF -
1LSB. Refer to Table 1 for the digital-to-analog (D/A)
codes.
The MAX1636 IC is rated for 30V input; however, the EV
kit is restricted to 22V operating range (25V absolute
maximum) due to the ratings of external components
and minimum duty-factor limitations.
Evaluates: MAX1636
Table 4. Jumper JU4 Functions
SHUNT
LOCATION
Off
On
MAX1636
OVP PIN
Connected to VCC
Connected to GND
OVERVOLTAGE
PROTECTION
Enabled
Disabled
The 2-pin header JU5 selects the shutdown mode.
Table 5 lists the selectable jumper options.
Table 5. Jumper JU5 Functions
SHUNT
LOCATION
On
Off
MAX1636
SHDN
PIN
Connected to GND
Connected to VIN
MAX1636
OUTPUT
Shutdown mode,
V
OUT
= 0V
MAX1636 enabled
Table 2. Jumper JU2 Functions
SHUNT
LOCATION
Off
MAX1636
SKIP
PIN
Connected to
GND
Connected to
VCC
OPERATING
MODE
Idle mode, pulse-skipping
operation for highest light-
load efficiency
Low-noise mode, fixed-fre-
quency PWM operation.
Latched Fault Protection
The MAX1636 contains a latched fault-protection circuit
that disables the IC when the output is overvoltage or
undervoltage (or when thermal shutdown is triggered).
Once disabled, the supply won’t attempt to restart until
input power is cycled or until
SHDN
(JU5) is cycled. A
fault condition can be triggered by overloading the out-
put, overvoltaging the output (which can happen when
changing the D/A code settings), or by touching sensi-
tive compensation or feedback nodes.
On
The 2-pin header JU3 selects the operating frequency.
Table 3 lists the selectable jumper options. The EV kit’s
components are selected for 300kHz operation.
Component values might need to be changed if 200kHz
operation is selected (refer to the
Design Procedure
section in the MAX1636 data sheet). Synchronize the
oscillator to an external clock signal by driving the
SYNC pad with a 5V amplitude pulse train in the 240kHz
to 350kHz frequency range.
Optional +5V Chip-Supply Input
An optional +5V supply input (Figure 1) can power the
IC and gate drivers to improve efficiency. The idea is to
power the IC from an efficient source (the +5V system
supply, typically 95% efficient) instead of relying on the
inefficient internal VL linear regulator. To test this fea-
ture, cut the trace at V+ to disable the linear regulator,
and connect an external +5V, 50mA supply to the
optional input.
Table 3. Jumper JU3 Functions
SHUNT
LOCATION
Off
On
MAX1636
SYNC PIN
Connected to VCC
Connected to GND
FREQUENCY
(kHz)
300
200
Alternate Op Amp for Lower
Supply Current
The MAX4332 op amp provided with this kit is very
accurate but draws up to 500µA supply current. For
improved supply current draw with a slight (0.4%)
degradation in output voltage accuracy, replace the
MAX4332 with a MAX4163, which draws 25µA (typ).
The 2-pin header JU4 selects the overvoltage protec-
tion. Table 4 lists the selectable jumper options.
_______________________________________________________________________________________
3
Evaluates: MAX1636
+5V (OPTIONAL)
C8
0.1µF
R7
R8
1M
13
V+ VCC
4
SHDN
RESET
5
8
N1
4
1
2
8
N2
10
GND
3
2
20
R14
2
JU3
8
SYNC
CSL
1
JU4
5
OVP
2
R15
1M
3
4
FB
C11
C18
OPEN
1500pF
1
8
VCC
0.1µF
14 0.1µF
VDD
12
13
16
NC CS WR
VCC
C5
C9
CC
CSH
1
1M
VCC
SKIP
PGND
1
D1
DL
2 JU2 1
4
L1
2.2µH
R1
0.01Ω
C15
470µF
6.3V
C14
470µF
6.3V
VOUT
3
C10
0.1µF 67
5
BST
DH
6 7
3
VL
12
20Ω 14
C13
4.7µF
16V
D2
CMPSH-3
C7
0.1µF
VIN
7V TO 22V
MAX1636 CPU Supply Evaluation Kit
Figure 1. MAX1636 EV Kit Schematic
SW1A
SW1B
SW1C
1
2
3
SW1D
4
VCC
X
C1
10µF
25V
C2
10µF
25V
C3
10µF
25V
C4
10µF
25V
JU5
R6
100k
ON / OFF
PGD
9
GND
U1
MAX1636
LX
REF
7
REF
R16
1M
C12
1µF
X
SENSE
VCC
SKIP
VCC
C16
470µF
6.3V
C17
OPEN
SYNC
R2
10k
0.1%
U3B
2
U3A
MAX4332
MAX4332
3
GND
R4
13.7k
0.1%
R3
110k
0.1%
15
VREF
2
5
7
6
D3
1
D7
4
D6
5
D5
6
D4
7
OUT1
U2
MAX5480
D3
8
D2
9
R5
51Ω
D2
_______________________________________________________________________________________
OUT2
D1
D0
10
11
8
R12
1M
7
6
5
R11
1M
R10
1M
R9
1M
VCC
D1
D0
X
= CUT HERE
4
MAX1636 CPU Supply Evaluation Kit
Evaluates: MAX1636
1.0"
1.0"
Figure 2. MAX1636 EV Kit Component Placement Guide—
Component Side
Figure 3. MAX1636 EV Kit Component Placement Guide—
Solder Side
_______________________________________________________________________________________
5

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