MAX797 ,Step-Down Controllers with Synchronous Rectifier for CPU PowerELECTRICAL CHARACTERISTICS(V+ = 15V, GND = PGND = 0V, I = I = 0A, T = 0°C to +70°C for MAX79_C, T = ..
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MAX796-MAX797
Step-Down Controllers with Synchronous Rectifier for CPU Power
_______________General DescriptionThe 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/MAX799are 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 SKIPoverride 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.
________________________ApplicationsNotebook and Subnotebook Computers
PDAs and Mobile Communicators
Cellular Phones
____________________________Features96% Efficiency4.5V to 30V Input Range2.5V to 6V Adjustable OutputPreset 3.3V and 5V Outputs (at up to 10A)Multiple Regulated Outputs+5V Linear-Regulator OutputPrecision 2.505V Reference OutputAutomatic Bootstrap Circuit150kHz/300kHz Fixed-Frequency PWM OperationProgrammable Soft-Start375µA Typ Quiescent Current (VIN= 12V, VOUT= 5V)1µA Typ Shutdown Current
MAX796/MAX797/MAX799
Step-Down Controllers with
Synchronous Rectifier for CPU Power
PARTMAX799
MAIN OUTPUTSPECIAL FEATURE3.3V/5V or adjRegulates negative secondary
voltage (such as -5V)
MAX7973.3V/5V or adjLogic-controlled low-noise mode
MAX7963.3V/5V or adjRegulates positive secondary
voltage (such as +12V)
Idle Mode is a trademark of Maxim Integrated Products.
19-0221; Rev 4; 9/05
___________________Pin ConfigurationBSTGND
REF
(SECFB) SKIP
TOP VIEW
MAX796
MAX797
MAX799PGND
CSL
( ) ARE FOR MAX796/ MAX799.
CSH
SHDN
SYNC
DIP/SODice*
16 Narrow SO
16 Plastic DIP
PIN-PACKAGETEMP RANGE0°C to +70°C
0°C to +70°C
0°C to +70°CMAX796C/D
MAX796CSE
MAX796CPE
PART†16 CERDIP
16 Narrow SO
16 Plastic DIP-40°C to +85°C
-40°C to +85°C
-55°C to +125°CMAX796MJE
MAX796ESE
MAX796EPE
Ordering Information continued at end of data sheet.*Contact factory for dice specifications.
_______________Ordering Information
EVALUATION KIT AVAILABLE
MAX796/MAX797/MAX799
Step-Down Controllers with
Synchronous Rectifier for CPU Power
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(V+ = 15V, GND = PGND = 0V, IVL= IREF= 0A, TA= 0°C to +70°C for MAX79_C, TA= 0°C to +85°C for MAX79_E, = -55°C to +125°C for MAX79_M, unless otherwise noted.)
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.
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
SHDNto 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 (TA= +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, 10s).....................................+300
Rising edge, hysteresis = 25mV
Rising edge, hysteresis = 15mV
SHDN= 2V, 0mA < IVL< 25mA, 5.5V < V+ < 30V
Falling edge, hysteresis = 20mV (MAX799)
CSH-CSL, negative
CSH-CSL, positive
Falling edge, hysteresis = 15mV (MAX796)
6V < V+ < 30V
25mV < (CSH-CSL) < 80mV
0mV < (CSH-CSL) < 80mV, FB = VL, 6V < V+ < 30V,
includes line and load regulation
External resistor divider
(CSH-CSL) = 0V
0mV < (CSH-CSL) < 80mV
CONDITIONS4.24.7VL/CSL Switchover Voltage3.84.1VL Fault Lockout Voltage4.75.3VL Output Voltage
-0.0500.05V2.452.5052.55SECFB Regulation Setpoint2.0SS Fault Sink Current2.54.06.5SS Source Current
5.030V4.530Input Supply Range
-50-100-160mV80100120Current-Limit Voltage
%/V0.040.06Line Regulation
1.54.855.105.255V Output Voltage (CSL)REF6Nominal Adjustable Output
Voltage Range2.432.5052.57Feedback Voltage2.5Load Regulation
UNITSMINTYPMAXPARAMETERMAX79_C
MAX79_E/M
0mV < (CSH-CSL) < 80mV, FB = 0V, 4.5V < V+ < 30V,
includes line and load regulation V3.203.353.463.3V Output Voltage (CSL)
+3.3V AND +5V STEP-DOWN CONTROLLERS
FLYBACK/PWM CONTROLLER
INTERNAL REGULATOR AND REFERENCE
MAX796/MAX797/MAX799
Step-Down Controllers with
Synchronous Rectifier for CPU Power
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.
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, GND = PGND = 0V, IVL= IREF= 0A, TA= 0°C to +70°C for MAX79_C, TA= 0°C to +85°C for MAX79_E, = -55°C to +125°C for MAX79_M, unless otherwise noted.)
SECFB, 0V or 4V
SHDN, 0V or 30V
SHDN, SKIP
SYNC
SYNC = 0V or 5V
No external load (Note 1)
SYNC = REF
Guaranteed by design
CSH = CSL = 6V
V+ = 4V, CSL = 0V (Note 2)
SYNC = 0V or 5V
SHDN= 0V, V+ = 30V,
CSL = 0V or 6V
Falling edge
0µA < IREF< 100µA
SYNC = REF
SHDN= 0V, CSL = 6V, V+ = 0V or 30V, VL = 0V
CONDITIONSMAX79_C
MAX79_E/M
Input Current
2.0VVL - 0.5Input High Voltage939691Maximum Duty Cycle
kHz190340Oscillator Sync Range200SYNC Rise/Fall Time200SYNC Low Pulse Width200SYNC High Pulse Width
125150175kHz270300330Oscillator Frequency
2.452.55V2.462.5052.54Reference Output Voltage4.86.6Quiescent Power Consumption48Dropout Power ConsumptionµA13V+ Shutdown Current1.82.3Reference Fault Lockout Voltage50Reference Load Regulation0.11CSL Shutdown Leakage Current
UNITSMINTYPMAXPARAMETERMAX79_C
MAX79_E/M
MAX79_C
MAX79_E/M
FB = CSH = CSL = 6V,
VL switched over to CSL15µA13V+ Off-State Leakage Current
DL forced to 2V
FB, FB = REF
CSH, CSL, CSH = CSL = 6V, device not shut down
SYNC, SKIP1DL Sink/Source Current
±100
SHDN, SKIP
SYNC
0.5V0.8Input Low Voltage
DH forced to 2V, BST-LX = 4.5VA1DH Sink/Source Current
High or low, BST-LX = 4.5V
High or low7DH On-Resistance7DL On-Resistance
OSCILLATOR AND INPUTS/OUTPUTSMAX796/MAX797/MAX799
Step-Down Controllers with
Synchronous Rectifier for CPU Power
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, GND = PGND = 0V, IVL= IREF= 0A, TA= -40°C to +85°C for MAX79_E, unless otherwise noted.) (Note 3)
Note 3:All -40°C to +85°C specifications above are guaranteed by design.
External resistor divider
0mV < (CSH - CSL) < 80mV, FB = VL, 4.5V < V+ < 30V,
includes line and load regulation
0mV < (CSH - CSL) < 80mV, FB = VL, 6V < V+ < 30V,
includes line and load regulation
CONDITIONSREF6.0Nominal Adjustable Output
Voltage Range3.103.353.563.3V Output Voltage (CSL)5.030Input Supply Range4.705.105.405V Output Voltage (CSL)
UNITSMINTYPMAXPARAMETERCSH - CSL, negative
(CSH-CSL) = 0V
6V < V+ < 30V
CSH - CSL, positive
-40-100-160Current-Limit Voltage2.402.60Feedback Voltage
%/V0.040.06Line Regulation70130
FB = CSH = CSL = 6V, VL switched over to CSL
SHDN= 0V, V+ = 30V, CSL = 0V or 6V
Rising edge, hysteresis = 25mV
No external load (Note 1)
0µA < IREF< 100µA110V+ Off-State Leakage Current110V+ Shutdown Current
Rising edge, hysteresis = 15mV
SHDN= 2V, 0mA < IVL< 25mA, 5.5V < V+ < 30V
4.24.7VL/CSL Switchover Voltage2.432.5052.57Reference Output Voltage
Falling edge, hysteresis = 15mV (MAX796)
Falling edge, hysteresis = 20mV (MAX799)50Reference Load Regulation3.754.05VL Fault Lockout Voltage4.75.3VL Output Voltage
2.402.60V-0.080.08SECFB Regulation Setpoint
SYNC = REF
SYNC = 0V or 5V91
kHz210320Oscillator Sync Range
kHzSYNC = REF
120150180Oscillator Frequency250SYNC High Pulse Width250SYNC Low Pulse Width
2503003504.88.4Quiescent Power Consumption
High or low, BST - LX = 4.5V
High or low
SYNC = 0V or 5V7DH On-Resistance7DL On-Resistance9396Maximum Duty Cycle
+3.3V and +5V STEP-DOWN CONTROLLERS
FLYBACK/PWM CONTROLLER
INTERNAL REGULATOR AND REFERENCE
OSCILLATOR AND INPUTS/OUTPUTS
MAX796/MAX797/MAX799
Step-Down Controllers with
Synchronous Rectifier for CPU Power SHDN
+12V
OUTPUT
+5V
OUTPUT
INPUT
6V TO 30V
BST
PGND
CSH
CSL
REF
SYNC
GND
SECFB
MAX796
__________________________________________________Typical Operating CircuitsMAX797
SHDN
+3.3V
OUTPUT
INPUT
4.5V TO 30V
BST
PGND
CSH
CSL
REF
SYNC
GND
SKIPFBVL
