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Details, datasheet, quote on part number:LM2631MTCX-ADJ
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Datasheet text preview:
LM2631 Synchronous Step-Down Power Supply Controller
April 1999
LM2631 Synchronous Step-Down Power Supply Controller
General Description
The LM2631 controller provides all the active functions for step-down (buck) switching converters. These dc-to-dc converters provide core CPU power in battery-operated systems. High efficiency is achieved by using synchronous rectification and pulse-skipping mode operation at light load. Inexpensive N-channel MOSFETs are used to reduce system cost. Bootstrap circuit is used to drive the high-side N-channel MOSFET. Current mode control scheme is used to improve line regulation and transient response, also provides cycle-by-cycle current limiting. The operating frequency is adjustable between 200 kHz and 400 kHz. An external shutdown pin can be used to disable the device and reduce the quiescent current to 0.1 µA. In low noise applications, bringing the FPWM pin high can force the device to operate in constant frequency mode. Other features include the external synchronization pin, and the PGOOD pin to indicate the state of the output voltage. Protection circuitry includes thermal shutdown, undervoltage and overvoltage shutdown protection, soft-start capability, and two levels of current limits: The first level simply limits the load current directly; at the second level, if the load pulls the output voltage down below 80% of the regulated value, the chip will shut down. This operation is disabled during startup, but an internal timer will enable it if the output does not come up in the preset time.
Features
n n n n n n n n n n n n n n n 4.5V to 30V input range Adjustable output (1.5V to 7V) 200 kHz to 400 kHz adjustable operating frequency Externally synchronizable On-board power good function Precision 1.24V reference output 0.8 mA typical quiescent current 0.1 µA shutdown current Thermal shutdown Direct current limit protection Input undervoltage lockout Output undervoltage shutdown protection Output overvoltage shutdown protection Programmable soft-start function Tiny TSSOP package
Applications
n n n n Notebook and subnotebook computers Cellular phones Portable instruments Battery-powered digital devices
Typical Application Circuit
DS100937-1
© 1999 National Semiconductor Corporation
DS100937
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Voltages from the indicated pins to GND and PGND: VIN CBOOT SD SW CSH, CSL FPWM, SYNC Power Dissipation (TA = 70°C), (Note 2) -0.3V to 32V -0.3V to 37V -0.3V to 32V -0.3V to 32V -0.3V to 8V -0.3V to 10V 720mW
Storage Temperature Range Soldering Dwell Time, Temperature (Note 3) Wave Infrared Vapor Phase ESD Rating (Note 4)
-65°C to +150°C
4 sec, 260°C 10 sec, 240°C 75 sec, 219°C 1.5 kV
Operating Ratings
VIN Junction Temperature 4.5V to 30V -25°C to +125°C
Electrical Characteristics
Specifications in standard type face are for Tj = 25°C and those with boldface type apply over full operating junction temperature range. VIN = 10V, GND = PGND = 0V,unless otherwise stated. (Notes 5, 6) Symbol System VIN VOUT VOUT/ VOUT VOUT/ VOUT IIN Input Supply Voltage Output Voltage Adjustment Range Load Regulation Line Regulation Input Supply Current with the Switching Controller ON Input Supply Current with the Switching Controller ON (Internal Rail is Supplied from CSL Pin) Input Supply Current with the IC Shut Down Minimum Output Voltage for CSL Providing the Internal Rail ISS Soft Start Source Current VSS = 1.5V 0 mV (CSH-CSL) 75 mV 4.5 VIN 30V VFB = 1V, VCSH = 2.15V, VCSL = 2.1V VFB = 1V, VCSH = 5.15V, VCSL = 5V VSD = 0V, VIN = 30V 4.5 30 1.5 7.0 0.3 0.002 0.8 1.2/1.4 0.15 0.1 3 (Note 7) 3 10 5 13 Soft Start Sink Current VCL Current Limit Voltage (Voltage from CSH to CSL) VIN Undervoltage Shutdown Latch Threshold VOUT Undervoltage Shutdown Latch Threshold (Note 8) VOUT Overvoltage Shutdown Latch Threshold (Note 8) VSS = 1.5V VFB = 1V, VCSL = 1.8V 20 110 90/80 130/140 Rising Edge 3.5 2.6 80 72/70 89/90 120 113/110 129/130 V(min) V(max) V(min) V(max) % %/V mA mA(max) mA µA µA(max) V µA µA(min) µA(max) µA mV mV(min) mV(max) V V(min) % VOUT % VOUT(min) %VOUT(max) % VOUT % VOUT(min) % VOUT(max) Parameter Conditions Typical Limit Units
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Electrical Characteristics
Symbol System Parameter
(Continued)
Specifications in standard type face are for Tj = 25°C and those with boldface type apply over full operating junction temperature range. VIN = 10V, GND = PGND = 0V,unless otherwise stated. (Notes 5, 6) Conditions Typical Limit Units
VOUT Low Regulation Comparator Enable Threshold Hysteresis of Low Regulation Comparator Regulator Window Detector Thresholds (PGOOD from High to Low) Regulator Window Detector Thresholds (PGOOD from Low to High) Gate Drive VBOOT IBOOT Bootstrap Voltage (Voltage from CBOOT to SW) CBOOT Leakage Current High Drive Source Current High Drive Sink Current Low Drive Source Current Low Drive Sink Current High-Side FET On-Resistance HDRV or LDRV Low-Side FET On-Resistance HDRV or LDRV Oscillator FOSC Oscillator Frequency FADJ Open CBOOT Sourcing 100 µA VCBOOT = 7V VHDRV = 0V, VCBOOT = 5V HDRV Forced to 5V LDRV Forced to 0V LDRV Forced to 5V
97 2 91 or 109
% VOUT % VOUT % VOUT
97 or 103
% VOUT
4.5 4.0 100 0.3 0.45 0.35 0.55 8 4
V V(min) nA A A A A
200 172/162 228/230
kHz kHz(min) kHz(max) kHz 255 345 kHz(min) kHz(max) V % 92 %(min) kHz(min)
Oscillator Frequency
FADJ Sourcing 2.94 µA (Note 9)
300
VFADJ DMAX
Voltage at FADJ pin Maximum Duty Cycle Maximum Frequency of Synchronization Minimum Pulse Width of the SYNC Signal FADJ Open Low-Going 200 ns Wide Rectangular Pulses Applied at 400 kHz at the SYNC Input SYNC Pulses are Low-Going
1.03 96
400
200
ns(min)
Error Amplifier IFB ICOMP Feedback Input Bias Current COMP Output Source Current COMP Output Sink Current Voltage Reference VREF Reference Voltage (Nominal)) IREF = 0µA 1.238 1.219/1.219 1.251/1.262 V V(min) V(max) VFB = 1.3V, VCSH = 5.15V, VCSL = 5V VCOMP = 0.2V, VFB = 1V VCOMP = 1.2V, VFB = 1.4V 100 50 50 nA µA µA
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