Step-Down Controllers with
Synchronous Rectifier for CPU Power
Table 1. Component Selection for Standard 3.3V Applications
COMPONENT
Input Range
Application
Frequency
Q1 High-Side
MOSFET
Q2 Low-Side
MOSFET
C1 Input
Capacitor
C2 Output
Capacitor
LOAD CURRENT
1A
4.75V to 18V
PDA
150kHz
2A
4.75V to 18V
Sub-Notebook
300kHz
3A
4.75V to 28V
Notebook
300kHz
Motorola
MMSF5N03HD or
Si9410
Motorola
MMSF5N03HD or
Si9410
4A
4.75V to 24V
High-End Notebook
300kHz
Motorola
MTD20N03HDL
DPAK
Motorola
MTD20N03HDL
DPAK
10A
4.5V to 6V
Desktop 5V-to-3V
300kHz
Motorola
MTD75N03HDL
D
2
PAK
Motorola
MTD75N03HDL
D
2
PAK
MAX796/MAX797/MAX799
Motorola 1/2
International Rectifier
MMDF3N03HD or 1/2
1/2 IRF7101
Si9936
Motorola 1/2
International Rectifier
MMDF3N03HD or 1/2
1/2 IRF7101
Si9936
22µF, 35V AVX TPS
or Sprague 595D
2 x 22µF, 35V AVX
TPS or Sprague 595D
2 x 220µF, 10V
2 x 22µF, 35V AVX
4 x 22µF, 35V AVX
Sanyo OS-CON
TPS or Sprague 595D TPS or Sprague 595D
10SA220M
220µF, 10V AVX TPS
or Sprague 595D
4 x 220µF, 10V
3 x 220µF, 10V AVX
Sanyo OS-CON
TPS or Sprague 595D
10SA220M
150µF, 10V AVX TPS 150µF, 10V AVX TPS
or Sprague 595D
or Sprague 595D
1N5817 Motorola
MBR0502L SOD-89
0.062Ω IRC
LR2010-01-R062
1N5817 NIEC
EC10QS02L or
Motorola MBRS130T3
0.039Ω IRC
LR2010-01-R039
D1 Rectifier
1N5819 NIEC
1N5821 NIEC
1N5820 NIEC
EC10QS03 or
NSQ03A04 or
NSQ03A02, or
Motorola MBRS130T3 Motorola MBRS340T3 Motorola MBRS340T3
0.025Ω IRC
LR2010-01-R025
10µH, 3A Ferrite
Sumida CDRH125
0.015Ω IRC
LR2010-01-015
3 x 0.02Ω IRC
LR2010-01-R020
(3 in parallel)
R1 Resistor
L1 Inductor
47µH, 1.2A Ferrite or
33µH, 2.2A Ferrite
Kool-Mu
Dale LPE6562-330MB
Sumida CD75-470
1.5µH, 11A, 3.5mΩ
4.7µH, 5.5A Ferrite
Coiltronics
Coilcraft DO3316-472
CTX03-12357-1
Table 2. Component Suppliers
MANUFACTURER
AVX
Central Semiconductor
Coilcraft
Coiltronics
Dale
International Rectifier
IRC
Kemet
Matsuo
Motorola
*
Distributor
USA PHONE
(803) 946-0690
(516) 435-1110
(847) 639-6400
(561) 241-7876
(605) 668-4131
(310) 322-3331
(512) 992-7900
(864) 963-6300
(714) 969-2491
(602) 303-5454
FACTORY FAX
[Country Code]
[1] 803-626-3123
[1] 516-435-1824
[1] 847-639-1469
[1] 561-241-9339
[1] 605-665-1627
[1] 310-322-3332
[1] 512-992-3377
[1] 864-963-6521
[1] 714-960-6492
[1] 602-994-6430
MANUFACTURER
Murata-Erie
NIEC
Sanyo
Siliconix
Sprague
Sumida
TDK
Transpower Technologies
USA PHONE
(814) 237-1431
(800) 831-9172
FACTORY FAX
[Country Code]
[1] 814-238-0490
(805) 867-2555* [81] 3-3494-7414
(619) 661-6835 [81] 7-2070-1174
(408) 988-8000
(800) 554-5565
(603) 224-1961
(847) 956-0666
(847) 390-4461
(702) 831-0140
[1] 408-970-3950
[1] 603-224-1430
[81] 3-3607-5144
{1} 847-390-4405
[1] 702-831-3521
losses due to MOSFET gate charge. The step-down
power-switching circuit consists of two N-channel
MOSFETs, a rectifier, and an LC output filter. The out-
put voltage is the average of the AC voltage at the
switching node, which is adjusted and regulated by
changing the duty cycle of the MOSFET switches. The
gate-drive signal to the N-channel high-side MOSFET
must exceed the battery voltage and is provided by a
flying capacitor boost circuit that uses a 100nF capaci-
tor connected to BST.
The MAX796 contains nine major circuit blocks, which
are shown in Figure 2.
11
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
