MAX797H Maxim, MAX797H Datasheet

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MAX797H

Manufacturer Part Number
MAX797H
Description
High-Voltage / Step-Down Controller with Synchronous Rectifier for CPU Power
Manufacturer
Maxim
Datasheet

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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
19-1239; Rev 0; 7/97
Idle Mode is a trademark of Maxim Integrated Products.
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.
_______________General Description
__________________Pin Configuration
TOP VIEW
Notebook and Subnotebook Computers
Industrial Controls
SHDN
SYNC
SKIP
GND
CSH
REF
SS
FB
________________________________________________________________ Maxim Integrated Products
High-Voltage, Step-Down Controller with
1
5
6
7
8
2
3
4
MAX797H
Synchronous Rectifier for CPU Power
SO
16
15
14
13
12
11
10
9
DH
LX
BST
DL
PGND
VL
V+
CSL
____________________________Features
__________Typical Operating Circuit
U.S. and foreign patents pending.
______________Ordering Information
MAX797HESE
+4.5V TO +30V
96% Efficiency
Up to 40V Power Input
2.5V to 6V Adjustable Output
Preset 3.3V and 5V Outputs (at up to 10A)
5V Linear-Regulator Output
Precision 2.505V Reference Output
Automatic Bootstrap Circuit
150kHz/300kHz Fixed-Frequency PWM Operation
Programmable Soft-Start
375µA Quiescent Current (V
1µA Shutdown Current
PART
SUPPLY
INPUT
SHDN
SS
REF
SYNC
GND
SKIP
V+
MAX797H
VL
FB
PGND
CSH
CSL
BST
DH
DL
LX
TEMP. RANGE
-40°C to +85°C
IN
+4V TO +40V
POWER INPUT
= 12V, V
16 Narrow SO
PIN-PACKAGE
OUT
= 5V)
OUTPUT
+3.3V
1

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MAX797H Summary of contents

Page 1

... 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. ...

Page 2

... REF Short Circuit to GND ...........................................Continuous VL Output Current ...............................................................50mA Continuous Power Dissipation (T SO (derate 8.70mW/°C above +70°C) ........................696mW Operating Temperature Range MAX797HESE .................................................-40°C to +85°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+300°C = 0°C to +85°C, SYNC = 0V, unless otherwise noted.) A CONDITIONS < ...

Page 3

... Oscillator Frequency SYNC = SYNC High Pulse Width SYNC Low Pulse Width SYNC Rise/Fall Time Guaranteed by design Oscillator Sync Range SYNC = REF Maximum Duty Factor SYNC = SYNC Input High Voltage SHDN, SKIP SYNC Input Low Voltage SHDN, SKIP SHDN 30V ...

Page 4

... Oscillator Frequency SYNC = SYNC High Pulse Width SYNC Low Pulse Width Oscillator Sync Range SYNC = REF Maximum Duty Factor SYNC = On-Resistance High or low DH On-Resistance High or low, BST - LX = 4.5V Note 1: Since the reference uses VL as its supply, V+ line-regulation error is insignificant. ...

Page 5

... High-Side Gate-Drive Output. DH normally drives the main buck switch floating driver output that 16 DH 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. _______________________________________________________________________________________ FUNCTION and V specifications) ...

Page 6

... The only difference between the two devices is in the BST pin’s absolute maximum rating. The MAX797H’s rating is 46V; the MAX797’s rating is 36V. The higher rating allows the MAX797H to use a power input up to 40V, provided that the V+ pin is powered by a separate supply between 4.5V and 30V. ...

Page 7

... This means that duty factor is not an issue except at the maximum input voltage and minimum output voltage. For example the lowest V that does not require less than the OUT _______________________________________________________________________________________ +5V REGULATED SUPPLY V+ VL SHDN MAX797H DH BST SS LX REF DL PGND SYNC CSH GND CSL SKIP FB minimum duty factor is 40V x 0 ...

Page 8

... Figure 3. Dividing the Power Input to Supply +40V POWER INPUT R1 Figure 5. Powering V+ with a Zener Dropping Diode ___________________Chip Information TRANSISTOR COUNT: 913 Printed USA is a registered trademark of Maxim Integrated Products. +8V TO +40V POWER INPUT 100k Q1 300k V+ VL MAX797H DH +20V TO +40V POWER INPUT 12V V+ VL SHDN MAX797H DH ...

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