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PDF MAX797H Data sheet ( Hoja de datos )
| Número de pieza | MAX797H | |
| Descripción | High-Voltage / Step-Down Controller with Synchronous Rectifier for CPU Power | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-1239; Rev 0; 7/97
High-Voltage, Step-Down Controller with
Synchronous Rectifier for CPU Power
_______________General Description
The MAX797H high-performance, step-down DC-DC
converter provides main CPU power in battery-powered
systems. A 40V rating on the power stage’s input allows
operation with high-cell-count batteries and a wide
range of AC adaptors. This buck controller achieves
96% efficiency by using synchronous rectification and
Maxim’s proprietary Idle Mode™ control scheme to
extend battery life at full-load (up to 10A) and no-load
outputs. Excellent dynamic response corrects output tran-
sients caused by the latest dynamic-clock CPUs within five
300kHz clock cycles. Unique bootstrap circuitry drives
inexpensive N-channel MOSFETs, reducing system cost
and eliminating the crowbar switching currents found in
some PMOS/NMOS switch designs.
The MAX797H has a logic-controlled and synchronizable
fixed-frequency, pulse-width-modulating (PWM) operating
mode, which reduces noise and RF interference in sensi-
tive mobile-communications and pen-entry applications.
The SKIP override input allows automatic switchover to
idle-mode operation (for high-efficiency pulse skipping) at
light loads, or forces fixed-frequency mode for lowest noise
at all loads. The MAX797H is pin compatible with the popu-
lar MAX797, but has a higher input voltage range.
The MAX797H comes in a 16-pin narrow SO package.
________________________Applications
Notebook and Subnotebook Computers
Industrial Controls
__________________Pin Configuration
TOP VIEW
SS 1
SKIP 2
REF 3
GND 4
SYNC 5
SHDN 6
FB 7
CSH 8
MAX797H
SO
16 DH
15 LX
14 BST
13 DL
12 PGND
11 VL
10 V+
9 CSL
____________________________Features
o 96% Efficiency
o Up to 40V Power Input
o 2.5V to 6V Adjustable Output
o Preset 3.3V and 5V Outputs (at up to 10A)
o 5V Linear-Regulator Output
o Precision 2.505V Reference Output
o Automatic Bootstrap Circuit
o 150kHz/300kHz Fixed-Frequency PWM Operation
o Programmable Soft-Start
o 375µA Quiescent Current (VIN = 12V, VOUT = 5V)
o 1µA Shutdown Current
______________Ordering Information
PART†
TEMP. RANGE
MAX797HESE
-40°C to +85°C
†U.S. and foreign patents pending.
PIN-PACKAGE
16 Narrow SO
__________Typical Operating Circuit
+4.5V TO +30V
SUPPLY
INPUT
V+
SHDN
VL
DH
MAX797H BST
+4V TO +40V
POWER INPUT
+3.3V
OUTPUT
SS LX
REF DL
PGND
SYNC
GND
SKIP
CSH
CSL
FB
Idle Mode is a trademark of Maxim Integrated Products.
________________________________________________________________ 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.
1 page  
High-Voltage, Step-Down Controller with
Synchronous Rectifier for CPU Power
______________________________________________________________Pin Description
PIN NAME
FUNCTION
1 SS Soft-Start Timing Capacitor Connection. Ramp time to full current limit is approximately 1ms/nF.
Disables pulse-skipping mode when high. Connect SKIP to GND for normal use. Do not leave unconnected.
2
SKIP
With SKIP grounded, the device automatically changes from pulse-skipping operation to full PWM operation
when the load current exceeds approximately 30% of maximum.
3 REF Reference Voltage Output. Bypass REF to GND with 0.33µF minimum.
4
GND
Low-noise Analog Ground and Feedback Reference Point
Oscillator Synchronization and Frequency Select. Tie SYNC to GND or VL for 150kHz operation; tie to REF for
5
SYNC
300kHz operation. A high-to-low transition begins a new cycle. Drive SYNC with 0V to 5V logic levels (see
Electrical Characteristics for VIH and VIL specifications). SYNC capture range is guaranteed to be 190kHz to
340kHz.
6
SHDN
Shutdown Control Input, Active Low. Logic threshold is set at approximately 1V (VTH of an internal N-channel
MOSFET). Tie SHDN to V+ for automatic start-up.
Feedback Input. Regulates at FB = REF (approximately 2.505V) in adjustable mode. FB is a Dual ModeTM
input that also selects the fixed-output voltage settings as follows:
• Connect to GND for 3.3V operation.
7 FB • Connect to VL for 5V operation.
• Connect to a resistor divider for adjustable mode. FB can be driven with 5V Rail-to-Rail® logic to change
the output voltage under system control.
8
CSH
Current-Sense Input, High Side. Current-limit level is 100mV referred to CSL.
9 CSL Current-Sense Input, Low Side. CSL also serves as the feedback input in fixed-output modes.
10
V+
Battery Voltage Input (4.5V to 30V). Bypass V+ to PGND close to the IC with a 0.1µF capacitor. Connects to a
linear regulator that powers VL.
5V Internal Linear-Regulator Output. VL is also the supply-voltage rail for the chip. It is switched to the output
11 VL voltage via CSL (VCSL > 4.5V) for automatic bootstrapping. Bypass to GND with 4.7µF. VL can supply up to
5mA for external loads.
12 PGND Power Ground
13 DL Low-Side Gate-Drive Output. DL normally drives the synchronous-rectifier MOSFET. Swings 0V to VL.
14 BST Boost Capacitor Connection for High-Side Gate Drive (0.1µF)
15 LX Switching Node (inductor) Connection. LX can swing 2V below ground without hazard.
16
DH
High-Side Gate-Drive Output. DH normally drives the main buck switch. It is a floating driver output that
swings from LX to BST, riding on the LX switching-node voltage.
Dual Mode is a trademark of Maxim Integrated Products.
Rail-to-Rail is a registered trademark of Nippon Motorola Ltd.
_______________________________________________________________________________________ 5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet MAX797H.PDF ] | |
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