19-0221; Rev 3a; 11/97
S
ANUAL
N KIT M EET
ATIO
A SH
EVALU
W DAT
FOLLO
Step-Down Controllers with
Synchronous Rectifier for CPU Power
____________________________Features
o
96% Efficiency
o
4.5V to 30V Input Range
o
2.5V to 6V Adjustable Output
o
o
o
o
Preset 3.3V and 5V Outputs (at up to 10A)
Multiple Regulated Outputs
+5V Linear-Regulator Output
Precision 2.505V Reference Output
_______________General Description
The MAX796/MAX797/MAX799 high-performance, step-
down DC-DC converters with single or dual outputs
provide main CPU power in battery-powered systems.
These buck controllers achieve 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 transients 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 MAX796/MAX799 are specially equipped with a sec-
ondary feedback input (SECFB) for transformer-based
dual-output applications. This secondary feedback path
improves cross-regulation of positive (MAX796) or nega-
tive (MAX799) auxiliary outputs.
The MAX797 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 MAX796/MAX797/MAX799 are all available in 16-
pin DIP and narrow SO packages. See the table below
to compare these three converters.
PART
MAX796
MAX797
MAX799
MAIN OUTPUT
3.3V/5V or adj.
3.3V/5V or adj.
3.3V/5V or adj.
SPECIAL FEATURE
Regulates positive secondary
voltage (such as +12V)
Logic-controlled low-noise mode
Regulates negative secondary
voltage (such as -5V)
MAX796/MAX797/MAX799
o
Automatic Bootstrap Circuit
o
150kHz/300kHz Fixed-Frequency PWM Operation
o
Programmable Soft-Start
o
375µA Typ Quiescent Current (V
IN
= 12V, V
OUT
= 5V)
o
1µA Typ Shutdown Current
______________Ordering Information
PART
†
MAX796CPE
MAX796CSE
MAX796C/D
MAX796EPE
MAX796ESE
MAX796MJE
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
PIN-PACKAGE
16 Plastic DIP
16 Narrow SO
Dice*
16 Plastic DIP
16 Narrow SO
16 CERDIP
Ordering Information continued at end of data sheet.
*Contact factory for dice specifications.
__________________Pin Configuration
TOP VIEW
SS 1
16 DH
15 LX
14 BST
________________________Applications
Notebook and Subnotebook Computers
PDAs and Mobile Communicators
Cellular Phones
(SECFB) SKIP 2
REF 3
GND 4
SYNC 5
SHDN 6
FB 7
CSH 8
MAX796
MAX797
MAX799
13 DL
12 PGND
11 VL
10 V+
9
CSL
Idle Mode is a trademark of Maxim Integrated Products.
†
U.S. and foreign patents pending.
DIP/SO
( ) ARE FOR MAX796/ MAX799.
________________________________________________________________
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.
Step-Down Controllers with
Synchronous Rectifier for CPU Power
MAX796/MAX797/MAX799
ABSOLUTE MAXIMUM RATINGS
V+ to GND .................................................................-0.3V, +36V
GND to PGND........................................................................±2V
VL to GND ...................................................................-0.3V, +7V
BST to GND ...............................................................-0.3V, +36V
DH to LX...........................................................-0.3V, BST + 0.3V
LX to BST.....................................................................-7V, +0.3V
SHDN to GND............................................................-0.3V, +36V
SYNC, SS, REF, FB, SECFB, SKIP, DL to GND..-0.3V, VL + 0.3V
CSH, CSL to GND .......................................................-0.3V, +7V
VL Short Circuit to GND..............................................Momentary
REF Short Circuit to GND ...........................................Continuous
VL Output Current ...............................................................50mA
Continuous Power Dissipation (T
A
= +70°C)
SO (derate 8.70mW/°C above +70°C) ........................696mW
Plastic DIP (derate 10.53mW/°C above +70°C) .........842mW
CERDIP (derate 10.00mW/°C above +70°C) ..............800mW
Operating Temperature Ranges
MAX79_C_ _ ......................................................0°C to +70°C
MAX79_E_ _....................................................-40°C to +85°C
MAX79_MJE .................................................-55°C to +125°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V+ = 15V, GND = PGND = 0V, I VL = I REF = 0A, T
A
= 0°C to +70°C for MAX79_C, T
A
= 0°C to +85°C for MAX79_E,
T
A
= -55°C to +125°C for MAX79_M, unless otherwise noted.)
PARAMETER
+3.3V AND +5V STEP-DOWN CONTROLLERS
Input Supply Range
5V Output Voltage (CSL)
3.3V Output Voltage (CSL)
Nominal Adjustable Output
Voltage Range
Feedback Voltage
Load Regulation
Line Regulation
Current-Limit Voltage
SS Source Current
SS Fault Sink Current
FLYBACK/PWM CONTROLLER
SECFB Regulation Setpoint
Falling edge, hysteresis = 15mV (MAX796)
Falling edge, hysteresis = 20mV (MAX799)
SHDN = 2V, 0mA < I
VL
< 25mA, 5.5V < V+ < 30V
Rising edge, hysteresis = 15mV
Rising edge, hysteresis = 25mV
2.45
-0.05
4.7
3.8
4.2
2.505
0
2.55
0.05
5.3
4.1
4.7
V
MAX79_C
MAX79_E/M
0mV < (CSH-CSL) < 80mV, FB = VL, 6V < V+ < 30V,
includes line and load regulation
0mV < (CSH-CSL) < 80mV, FB = 0V, 4.5V < V+ < 30V,
includes line and load regulation
External resistor divider
(CSH-CSL) = 0V
0mV < (CSH-CSL) < 80mV
25mV < (CSH-CSL) < 80mV
6V < V+ < 30V
CSH-CSL, positive
CSH-CSL, negative
80
-50
2.5
2.0
4.5
5.0
4.85
3.20
REF
2.43
2.505
2.5
1.5
0.04
100
-100
4.0
0.06
120
-160
6.5
5.10
3.35
30
30
5.25
3.46
6
2.57
V
V
V
V
V
%
%/V
mV
µA
mA
CONDITIONS
MIN
TYP
MAX
UNITS
INTERNAL REGULATOR AND REFERENCE
VL Output Voltage
VL Fault Lockout Voltage
VL/CSL Switchover Voltage
V
V
V
2
_______________________________________________________________________________________
Step-Down Controllers with
Synchronous Rectifier for CPU Power
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 15V, GND = PGND = 0V, I VL = I REF = 0A, T
A
= 0°C to +70°C for MAX79_C, T
A
= 0°C to +85°C for MAX79_E,
T
A
= -55°C to +125°C for MAX79_M, unless otherwise noted.)
PARAMETER
Reference Output Voltage
Reference Fault Lockout Voltage
Reference Load Regulation
CSL Shutdown Leakage Current
V+ Shutdown Current
V+ Off-State Leakage Current
Dropout Power Consumption
Quiescent Power Consumption
CONDITIONS
No external load (Note 1)
Falling edge
0µA < I
REF
< 100µA
SHDN = 0V, CSL = 6V, V+ = 0V or 30V, VL = 0V
SHDN = 0V, V+ = 30V,
CSL = 0V or 6V
FB = CSH = CSL = 6V,
VL switched over to CSL
V+ = 4V, CSL = 0V (Note 2)
CSH = CSL = 6V
SYNC = REF
SYNC = 0V or 5V
270
125
200
200
Guaranteed by design
190
SYNC = REF
SYNC = 0V or 5V
SYNC
SHDN, SKIP
SYNC
SHDN, SKIP
SHDN, 0V or 30V
SECFB, 0V or 4V
Input Current
SYNC, SKIP
CSH, CSL, CSH = CSL = 6V, device not shut down
FB, FB = REF
DL Sink/Source Current
DH Sink/Source Current
DL On-Resistance
DH On-Resistance
DL forced to 2V
DH forced to 2V, BST-LX = 4.5V
High or low
High or low, BST-LX = 4.5V
1
1
7
7
89
93
VL - 0.5
2.0
0.8
0.5
2.0
0.1
1.0
50
±100
nA
A
A
Ω
Ω
µA
91
96
200
340
MAX79_C
MAX79_E/M
MAX79_C
MAX79_E/M
0.1
1
1
1
1
4
4.8
300
150
MAX79_C
MAX79_E/M
MIN
2.46
2.45
1.8
TYP
2.505
MAX
2.54
2.55
2.3
50
1
3
5
3
5
8
6.6
330
175
UNITS
V
V
mV
µA
µA
µA
mW
mW
MAX796/MAX797/MAX799
OSCILLATOR AND INPUTS/OUTPUTS
Oscillator Frequency
SYNC High Pulse Width
SYNC Low Pulse Width
SYNC Rise/Fall Time
Oscillator Sync Range
Maximum Duty Cycle
Input High Voltage
Input Low Voltage
kHz
ns
ns
ns
kHz
%
V
V
Note 1:
Since the reference uses VL as its supply, V+ line-regulation error is insignificant.
Note 2:
At very low input voltages, quiescent supply current may increase due to excess PNP base current in the VL linear
regulator. This occurs only if V+ falls below the preset VL regulation point (5V nominal). See the Quiescent Supply Current
vs. Supply Voltage graph in the
Typical Operating Characteristics.
_______________________________________________________________________________________
3
Step-Down Controllers with
Synchronous Rectifier for CPU Power
MAX796/MAX797/MAX799
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 15V, GND = PGND = 0V, IVL = IREF = 0A, T
A
= -40°C to +85°C for MAX79_E, unless otherwise noted.) (Note 3)
PARAMETER
+3.3V and +5V STEP-DOWN CONTROLLERS
Input Supply Range
5V Output Voltage (CSL)
3.3V Output Voltage (CSL)
Nominal Adjustable Output
Voltage Range
Feedback Voltage
Line Regulation
Current-Limit Voltage
FLYBACK/PWM CONTROLLER
SECFB Regulation Setpoint
Falling edge, hysteresis = 15mV (MAX796)
Falling edge, hysteresis = 20mV (MAX799)
SHDN
= 2V, 0mA < I
VL
< 25mA, 5.5V < V+ < 30V
Rising edge, hysteresis = 15mV
Rising edge, hysteresis = 25mV
No external load (Note 1)
0µA < I
REF
< 100µA
SHDN
= 0V, V+ = 30V, CSL = 0V or 6V
FB = CSH = CSL = 6V, VL switched over to CSL
1
1
4.8
SYNC = REF
SYNC = 0V or 5V
250
120
250
250
210
SYNC = REF
SYNC = 0V or 5V
High or low
High or low, BST - LX = 4.5V
89
93
91
96
7
7
320
300
150
2.40
-0.08
4.7
3.75
4.2
2.43
2.505
2.60
0.08
5.3
4.05
4.7
2.57
50
10
10
8.4
350
180
V
0mV < (CSH - CSL) < 80mV, FB = VL, 6V < V+ < 30V,
includes line and load regulation
0mV < (CSH - CSL) < 80mV, FB = VL, 4.5V < V+ < 30V,
includes line and load regulation
External resistor divider
(CSH-CSL) = 0V
6V < V+ < 30V
CSH - CSL, positive
CSH - CSL, negative
70
-40
-100
5.0
4.70
3.10
REF
2.40
0.04
5.10
3.35
30
5.40
3.56
6.0
2.60
0.06
130
-160
V
V
V
V
V
%/V
mV
CONDITIONS
MIN
TYP
MAX
UNITS
INTERNAL REGULATOR AND REFERENCE
VL Output Voltage
VL Fault Lockout Voltage
VL/CSL Switchover Voltage
Reference Output Voltage
Reference Load Regulation
V+ Shutdown Current
V+ Off-State Leakage Current
Quiescent Power Consumption
OSCILLATOR AND INPUTS/OUTPUTS
Oscillator Frequency
SYNC High Pulse Width
SYNC Low Pulse Width
Oscillator Sync Range
Maximum Duty Cycle
DL On-Resistance
DH On-Resistance
kHz
ns
ns
kHz
%
Ω
Ω
V
V
V
V
mV
µA
µA
mW
Note 3:
All -40°C to +85°C specifications above are guaranteed by design.
4
_______________________________________________________________________________________
Step-Down Controllers with
Synchronous Rectifier for CPU Power
__________________________________________________Typical Operating Circuits
INPUT
4.5V TO 30V
MAX796/MAX797/MAX799
V+
SHDN
VL
MAX797
DH
+3.3V
OUTPUT
BST
SS
REF
LX
DL
PGND
SYNC
GND
SKIP
FB
CSH
CSL
INPUT
6V TO 30V
V+
SECFB
SHDN
FB
VL
+12V
OUTPUT
MAX796
DH
+5V
OUTPUT
BST
LX
DL
SS
REF
GND
SYNC
PGND
CSH
CSL
_______________________________________________________________________________________
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