MAXIM MAX796, MAX797, MAX799 User Manual

19-0221; Rev 4; 9/05
EVALUATION KIT
AVAILABLE
Step-Down Controllers with
Synchronous Rectifier for CPU Power
_______________General Description
The MAX796/MAX797/MAX799 high-performance, step­down 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 sec­ondary feedback input (SECFB) for transformer-based dual-output applications. This secondary feedback path improves cross-regulation of positive (MAX796) or nega­tive (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 sensi­tive 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 16­pin DIP and narrow SO packages. See the table below to compare these three converters.
PART
MAX796 3.3V/5V or adj
MAX797 3.3V/5V or adj Logic-controlled low-noise mode
MAX799
MAIN OUTPUT SPECIAL FEATURE
Regulates positive secondary voltage (such as +12V)
3.3V/5V or adj
Regulates negative secondary voltage (such as -5V)
________________________Applications
Notebook and Subnotebook Computers
PDAs and Mobile Communicators
Cellular Phones
____________________________Features
96% Efficiency
4.5V to 30V Input Range
2.5V to 6V Adjustable Output
Preset 3.3V and 5V Outputs (at up to 10A)
Multiple Regulated Outputs
+5V Linear-Regulator Output
Precision 2.505V Reference Output
Automatic Bootstrap Circuit
150kHz/300kHz Fixed-Frequency PWM Operation
Programmable Soft-Start
375µA Typ Quiescent Current (VIN= 12V, V
OUT
= 5V)
1µA Typ Shutdown Current
_______________Ordering Information
PART
MAX796CPE
MAX796CSE
MAX796EPE
MAX796ESE
Ordering Information continued at end of data sheet.
*Contact factory for dice specifications.
0°C to +70°C
0°C to +70°C
0°C to +70°CMAX796C/D
-40°C to +85°C
-55°C to +125°CMAX796MJE
PIN-PACKAGETEMP RANGE
16 Plastic DIP
16 Narrow SO
Dice*
16 Plastic DIP-40°C to +85°C
16 Narrow SO
16 CERDIP
___________________Pin Configuration
TOP VIEW
(SECFB) SKIP
REF
GND
SYNC
SHDN
CSH
SS
1
2
3
MAX796
4
MAX797
5
MAX799
6
FB
7
8
DH
16
LX
15
BST
14
DL
13
PGND
12
VL
11
V+
10
CSL
9
MAX796/MAX797/MAX799
Idle Mode is a trademark of Maxim Integrated Products.
U
________________________________________________________________ Maxim Integrated Products 1
( ) ARE FOR MAX796/ MAX799.
DIP/SO
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
MAX796/MAX797/MAX799
Step-Down Controllers with Synchronous Rectifier for CPU Power
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V+ = 15V, GND = PGND = 0V, IVL= I
REF
= 0A, TA= 0°C to +70°C for MAX79_C, TA= 0°C to +85°C for MAX79_E,
T
A
= -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
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, 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
CONDITIONS
V4.2 4.7VL/CSL Switchover Voltage
V3.8 4.1VL Fault Lockout Voltage
V4.7 5.3VL Output Voltage
-0.05 0 0.05
V
2.45 2.505 2.55
SECFB Regulation Setpoint
mA2.0SS Fault Sink Current
µA2.5 4.0 6.5SS Source Current
5.0 30
V
4.5 30
Input Supply Range
-50 -100 -160
mV
80 100 120
Current-Limit Voltage
%/V0.04 0.06Line Regulation
1.5
V4.85 5.10 5.255V Output Voltage (CSL)
VREF 6
Nominal Adjustable Output Voltage Range
V2.43 2.505 2.57Feedback Voltage
%
2.5
Load Regulation
UNITSMIN TYP MAXPARAMETER
MAX79_C
MAX79_E/M
0mV < (CSH-CSL) < 80mV, FB = 0V, 4.5V < V+ < 30V, includes line and load regulation
V3.20 3.35 3.463.3V 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
_______________________________________________________________________________________ 3
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= I
REF
= 0A, TA= 0°C to +70°C for MAX79_C, TA= 0°C to +85°C for MAX79_E,
T
A
= -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 < I
REF
< 100µA
SYNC = REF
SHDN = 0V, CSL = 6V, V+ = 0V or 30V, VL = 0V
CONDITIONS
0.1
MAX79_C
µA
2.0
MAX79_E/M
Input Current
2.0
V
VL - 0.5
Input High Voltage
%
93 96
89 91
Maximum Duty Cycle
kHz190 340Oscillator Sync Range
ns200SYNC Rise/Fall Time
ns200SYNC Low Pulse Width
ns200SYNC High Pulse Width
125 150 175
kHz
270 300 330
Oscillator Frequency
2.45 2.55
V
2.46 2.505 2.54
Reference Output Voltage
mW4.8 6.6Quiescent Power Consumption
mW48Dropout Power Consumption
15
µA
13
V+ Shutdown Current
V1.8 2.3Reference Fault Lockout Voltage
mV50Reference Load Regulation
µA0.1 1CSL Shutdown Leakage Current
UNITSMIN TYP MAXPARAMETER
MAX79_C
MAX79_E/M
MAX79_C
MAX79_E/M
FB = CSH = CSL = 6V, VL switched over to CSL
15
µA
13
V+ Off-State Leakage Current
DL forced to 2V
FB, FB = REF
CSH, CSL, CSH = CSL = 6V, device not shut down
SYNC, SKIP
A1DL Sink/Source Current
±100
50
1.0
SHDN, SKIP
SYNC
0.5
V
0.8
Input Low Voltage
DH forced to 2V, BST-LX = 4.5V A1DH Sink/Source Current
High or low, BST-LX = 4.5V
High or low
7DH On-Resistance
7DL On-Resistance
OSCILLATOR AND INPUTS/OUTPUTS
nA
MAX796/MAX797/MAX799
Step-Down Controllers with Synchronous Rectifier for CPU Power
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 15V, GND = PGND = 0V, IVL= I
REF
= 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
CONDITIONS
VREF 6.0
Nominal Adjustable Output Voltage Range
V3.10 3.35 3.563.3V Output Voltage (CSL)
V5.0 30Input Supply Range
V4.70 5.10 5.405V Output Voltage (CSL)
UNITSMIN TYP MAXPARAMETER
CSH - CSL, negative
(CSH-CSL) = 0V
6V < V+ < 30V
CSH - CSL, positive
-40 -100 -160
Current-Limit Voltage
V2.40 2.60Feedback Voltage
%/V0.04 0.06Line Regulation
mV
70 130
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 < I
REF
< 100µA
µA110V+ Off-State Leakage Current
µA110V+ Shutdown Current
V
Rising edge, hysteresis = 15mV
SHDN = 2V, 0mA < IVL< 25mA, 5.5V < V+ < 30V
4.2 4.7VL/CSL Switchover Voltage
V2.43 2.505 2.57Reference Output Voltage
Falling edge, hysteresis = 15mV (MAX796)
Falling edge, hysteresis = 20mV (MAX799)
mV50Reference Load Regulation
V3.75 4.05VL Fault Lockout Voltage
V4.7 5.3VL Output Voltage
2.40 2.60 V
-0.08 0.08
SECFB Regulation Setpoint
SYNC = REF
SYNC = 0V or 5V
89 91
kHz210 320Oscillator Sync Range
kHz
SYNC = REF
120 150 180
Oscillator Frequency
ns250SYNC High Pulse Width
ns250SYNC Low Pulse Width
250 300 350
mW4.8 8.4Quiescent Power Consumption
High or low, BST - LX = 4.5V
High or low
SYNC = 0V or 5V
7DH On-Resistance
7DL On-Resistance
%
93 96
Maximum 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
_______________________________________________________________________________________ 5
SHDN
DH
+12V
OUTPUT
+5V
OUTPUT
INPUT
6V TO 30V
BST
LX
DL
PGND
CSH
CSL
SS
REF
SYNC
GND
V+
VL
FB
SECFB
MAX796
__________________________________________________Typical Operating Circuits
MAX797
SHDN
DH
+3.3V
OUTPUT
INPUT
4.5V TO 30V
BST
LX
DL
PGND
CSH
CSL
SS
REF
SYNC
GND
SKIP FB
V+ VL
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
100
50
0.001 10.10.01 10
EFFICIENCY
vs. LOAD CURRENT, 5V/3A CIRCUIT
60
MAX796-01
LOAD CURRENT (A)
EFFICIENCY (%)
70
80
90
STANDARD MAX797 5V/3A CIRCUIT, FIGURE 1 f = 300kHz
VIN = 6V
VIN = 30V
100
50
0.001 10.10.01 10
EFFICIENCY
vs. LOAD CURRENT, 3.3V/3A CIRCUIT
60
MAX796-02
LOAD CURRENT (A)
EFFICIENCY (%)
70
80
90
STANDARD MAX797 3.3V/3A CIRCUIT, FIGURE 1 f = 300kHz
VIN = 12V
VIN = 30V
VIN = 5V
100
40
50
60
70
80
90
0.1 1 10
EFFICIENCY
vs. LOAD CURRENT, 3.3V/10A CIRCUIT
MAX796-03
LOAD CURRENT (A)
EFFICIENCY (%)
SKIP = LOW
SKIP = HIGH
STANDARD MAX797 3.3V/10A CIRCUIT, FIGURE 1 f = 300kHz V
IN
= 5V
MAX796/MAX797/MAX799
Step-Down Controllers with Synchronous Rectifier for CPU Power
6 _______________________________________________________________________________________
MAX799
SHDN
DH
–5V OUTPUT
+5V OUTPUT
INPUT 6V TO 30V
BST
LX
DL
PGND
CSH
CSL
SS
REF
FROM
REF
SYNC
GND
V+
VL
FB
SECFB
_____________________________________Typical Operating Circuits (continued)
MAX796/MAX797/MAX799
Step-Down Controllers with
Synchronous Rectifier for CPU Power
_______________________________________________________________________________________ 7
____________________________Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
0
200µ
400µ
600µ
800µ
14m
15m
16m
048121620242832
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE,
5V/3A CIRCUIT IN IDLE MODE
MAX796-04
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (A)
STANDARD MAX797 APPLICATION CONFIGURED FOR 5V SKIP = LOW SYNC = REF
0
0.2
0.4
0.6
0.8
1.2
1.0
1.4
1.6
048121620242832
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX796-07
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
DEVICE CURRENT ONLY SHDN = LOW
0
200
400
600
800
1200
1000
1400
048121620242832
MAX796-05
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE,
3.3V/3A CIRCUIT IN IDLE MODE
STANDARD MAX797 3.3V/3A CIRCUIT, FIGURE 1 SKIP = LOW SYNC = REF
SWITCHING
NOT SWITCHING (FB FORCED TO 3.5V)
0
10
20
30
048121620242832
MAX796-06
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE, LOW-NOISE MODE
f = 150kHz
f = 300kHz
STANDARD MAX797 3.3V/3A CIRCUIT, FIGURE 1 SKIP = HIGH
0
0.01 1 100.1
DROPOUT VOLTAGE
vs. LOAD CURRENT
200
100
300
400
500
600
700
800
MAX796-08
LOAD CURRENT (A)
V
IN
- V
OUT
(mV)
STANDARD MAX797 APPLICATION CONFIGURED FOR 5V V
OUT
> 4.8V
f = 150kHz
f = 300kHz
0
1 100 100010
REF LOAD-REGULATION ERROR
vs. LOAD CURRENT
5
10
15
20
MAX796-09
REF LOAD CURRENT (µA)
LOAD REGULATION V (mV)
0
200
100
300
400
500
020406080
MAX796-10
VL LOAD CURRENT (mA)
LOAD REGULATION V (mV)
VL LOAD-REGULATION ERROR
vs. LOAD CURRENT
0
50
100
150
200
250
300
350
400
450
048121620242832
MAX796-11
SUPPLY VOLTAGE (V)
MAXIMUM SECONDARY CURRENT (mA)
MAX796
MAXIMUM SECONDARY CURRENT
vs. SUPPLY VOLTAGE, 5V/15V CIRCUIT
I
OUT
(MAIN) = 0A
I
OUT
(MAIN) = 3A
CIRCUIT OF FIGURE 11 TRANSFORMER = TTI5870 V
SEC
> 12.75V
1000
0.1
100µ 10m 1
SWITCHING FREQUENCY
vs. LOAD CURRENT
10
LOAD CURRENT (A)
SWITCHING FREQUENCY (kHz)
100
1m 100m
SYNC = REF (300kHz) SKIP = LOW
+5V, VIN = 7.5V
1
+5V, VIN = 30V
+3.3V, VIN = 7.5V
I
LOAD
= 100mA, VIN = 10V,
CIRCUIT OF FIGURE 1
IDLE-MODE WAVEFORMS
+5V OUTPUT 50mV/div
2V/div
200µs/div
I
LOAD
= 1A, VIN = 16V,
CIRCUIT OF FIGURE 1
PULSE-WIDTH-MODULATION MODE WAVEFORMS
LX VOLTAGE 10V/div
+5V OUTPUT VOLTAGE 50mV/div
500ns/div
VIN = 15V, CIRCUIT OF FIGURE 1
+5V LOAD-TRANSIENT RESPONSE
+5V OUTPUT 50mV/div
3A
0A
LOAD CURRENT
200µs/div
MAX796/MAX797/MAX799
Step-Down Controllers with Synchronous Rectifier for CPU Power
8 _______________________________________________________________________________________
0
150
300
450
600
900
750
1050
03691215 18 21 24
MAX796
MAXIMUM SECONDARY CURRENT
vs. SUPPLY VOLTAGE, 3.3V/5V CIRCUIT
MAX796-12
SUPPLY VOLTAGE (V)
MAXIMUM SECONDARY CURRENT (mA)
I
OUT
(MAIN) = 2A
I
OUT
(MAIN) = 0A
CIRCUIT OF FIGURE 12 TRANSFORMER = TDK 1.5:1 V
SEC
4.8V
0
100
200
300
400
600
500
700
800
048121620242832
MAX799
MAXIMUM SECONDARY CURRENT
vs. SUPPLY VOLTAGE, ±5V CIRCUIT
MAX796-13
SUPPLY VOLTAGE (V)
MAXIMUM SECONDARY CURRENT (mA)
CIRCUIT OF FIGURE 13 TRANSFORMER = TTI5926 V
SEC
-5.1V
I
OUT
(MAIN) = 0A
I
OUT
(MAIN) = 1A
____________________________Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX796/MAX797/MAX799
Step-Down Controllers with
Synchronous Rectifier for CPU Power
_______________________________________________________________________________________ 9
______________________________________________________________Pin Description
Current-Sense input, High side. Current-limit level is 100mV referred to CSL.CSH8
Current-Sense input, Low side. Also serves as the feedback input in fixed-output modes.CSL9
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.
V+10
5V Internal linear-regulator output. VL is also the supply voltage rail for the chip. VL is switched to the output voltage via CSL (V
CSL
> 4.5V) for automatic bootstrapping. Bypass to GND with 4.7µF. VL can
supply up to 5mA for external loads.
VL11
Power Ground.PGND12
Low-noise analog Ground and feedback reference point.GND4
Oscillator Synchronization and frequency select. Tie to GND or VL for 150kHz operation; tie to REF for 300kHz operation. A high-to-low transition begins a new cycle. Drive SYNC with 0V to 5V logic levels (see the Electrical Characteristics table for VIHand VILspecifications). SYNC capture range is 190kHz to 340kHz guaranteed.
SYNC5
Shutdown control input, active low. Logic threshold is set at approximately 1V (VTHof an internal N-channel MOSFET). Tie SHDN to V+ for automatic start-up.
SHDN6
Feedback input. Regulates at FB = REF (approximately 2.505V) in adjustable mode. FB is a Dual-Mode
TM
input that also selects the fixed output voltage settings as follows:
Connect to GND for 3.3V operation.
Connect to VL for 5V operation.
Connect FB to a resistor divider for adjustable mode. FB can be driven with +5V rail-to-rail logic in order to
change the output voltage under system control.
FB7
Reference voltage output. Bypass to GND with 0.33µF minimum.REF3
PIN
Secondary winding Feedback input. Normally connected to a resistor divider from an auxiliary output.
Don’t leave SECFB unconnected.
MAX796: SECFB regulates at VSECFB = 2.505V. Tie to VL if not used.
MAX799: SECFB regulates at VSECFB = 0V. Tie to a negative voltage through a high-value current-limit-
ing resistor (I
MAX
= 100µA) if not used.
SECFB
(MAX796/
MAX799)
2
Soft-Start timing capacitor connection. Ramp time to full current limit is approximately 1ms/nF.SS1
FUNCTIONNAME
Low-side gate-drive output. Normally drives the synchronous-rectifier MOSFET. Swings 0V to VL.DL13
Boost capacitor connection for high-side gate drive (0.1µF). BST14
Switching node (inductor) connection. Can swing 2V below ground without hazard.LX15
High-side gate-drive output. Normally drives the main buck switch. DH is a floating driver output that swings from LX to BST, riding on the LX switching-node voltage.
DH16
Dual Mode is a trademark of Maxim Integrated Products.
Disables pulse-skipping mode when high. Connect to GND for normal use. Don’t leave SKIP unconnected. With SKIP
grounded, the device will automatically change from pulse-skipping operation to full PWM opera-
tion when the load current exceeds approximately 30% of maximum. (See Table 3.)
SKIP
(MAX797)
MAX796/MAX797/MAX799
Step-Down Controllers with Synchronous Rectifier for CPU Power
10 ______________________________________________________________________________________
______Standard Application Circuit
It is easy to adapt the basic MAX797 single-output 3.3V buck converter (Figure 1) to meet a wide range of applications with inputs up to 28V (limited by choice of external MOSFET). Simply substitute the appropriate components from Table 1. These circuits represent a good set of tradeoffs between cost, size, and efficiency while staying within the worst-case specification limits for stress-related parameters such as capacitor ripple current. Each of these circuits is rated for a continuous load current at TA= +85°C, as shown. The 1A, 2A and 10A applications can withstand a continuous output short-circuit to ground. The 3A and 5A applications can withstand a short circuit of many seconds duration, but the synchronous-rectifier MOSFET overheats, exceed­ing the manufacturer’s ratings for junction temperature by 50°C or more.
If the 3A or 5A circuit must be guaranteed to withstand a continuous output short circuit indefinitely, see the section MOSFET Switches under Selecting Other Components. Don’t change the frequency of these cir­cuits without first recalculating component values (par­ticularly inductance value at maximum battery voltage).
_______________Detailed Description
The MAX796 is a BiCMOS, switch-mode power-supply controller designed primarily for buck-topology regula­tors in battery-powered applications where high effi­ciency and low quiescent supply current are critical. The MAX796 also works well in other topologies such as boost, inverting, and CLK due to the flexibility of its floating high-speed gate driver. Light-load efficiency is enhanced by automatic idle-mode operation—a vari­able-frequency pulse-skipping mode that reduces
MAX797
CSL
CSH
VL
SYNC
FB
V+
10 11
57
14
Q1
Q2
16
15
13
D2 CMPSH-3
J1 150kHz/300kHz JUMPER
NOTE: KEEP CURRENT-SENSE LINES SHORT AND CLOSE TOGETHER. SEE FIG. 10
D1
12
8
9
REF
3
GND
4
+5V AT 5mA
+3.3V OUTPUT
GND OUT
BST
DH
LX
DL
2
1
LOW-NOISE
CONTROL
PGND
SKIP
SS
6
ON/OFF
CONTROL
SHDN
INPUT
REF OUTPUT +2.505V AT 100µA
C5
0.33µF
C4
4.7µF
C7
0.1µF
C6
0.01µF
(OPTIONAL)
C1
C2
C3
0.1µF
R1
L1
Figure 1. Standard 3.3V Application Circuit
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