May 2003
LM3478
High Efficiency Low-Side N-Channel Controller for
Switching Regulator
General Description
The LM3478 is a versatile Low-Side N-FET switching regulator controller. It is suitable for use in topologies requiring low side FET, such as boost, flyback, SEPIC, etc. Moreover, the LM3478 can be operated at extremely high switching frequency in order to reduce the overall solution size. The switching frequency of LM3478 can be adjusted to any value between 100kHz and 1MHz by using a single external resistor. Current mode control provides superior bandwidth and transient response, besides cycle-by-cycle current limiting. Output current can be programmed with a single external resistor.
The LM3478 has built in features such as thermal shutdown, short-circuit protection, over voltage protection, etc. Power saving shutdown mode reduces the total supply current to 5µA and allows power supply sequencing. Internal soft-start limits the inrush current at start-up.
Key Specifications
nWide supply voltage range of 2.97V to 40V
n100kHz to 1MHz Adjustable clock frequency
n±2.5% (over temperature) internal reference
n 10µA shutdown current (over temperature)
Features
n8-lead Mini-SO8 (MSOP-8) package
nInternal push-pull driver with 1A peak current capability
nCurrent limit and thermal shutdown
nFrequency compensation optimized with a capacitor and a resistor
nInternal softstart
nCurrent Mode Operation
nUndervoltage Lockout with hysteresis
Applications
nDistributed Power Systems
nBattery Chargers
nOffline Power Supplies
nTelecom Power Supplies
nAutomotive Power Systems
Typical Application Circuit
10135501
Typical High Efficiency Step-Up (Boost) Converter
Regulator Switching for Controller Channel-N Side-Low Efficiency High LM3478
© 2003 National Semiconductor Corporation |
DS101355 |
www.national.com |
LM3478
Connection Diagram
10135502
8 Lead Mini SO8 Package (MSOP-8 Package)
Package Marking and Ordering Information
Order Number |
Package Type |
Package Marking |
Supplied As: |
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LM3478MM |
MSOP-8 |
S14B |
1000 units on Tape and |
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Reel |
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LM3478MMX |
MSOP-8 |
S14B |
3500 units on Tape and |
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Reel |
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Pin Description
Pin Name |
Pin Number |
Description |
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ISEN |
1 |
Current sense input pin. Voltage generated across an external |
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sense resistor is fed into this pin. |
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COMP |
2 |
Compensation pin. A resistor, capacitor combination connected to |
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this pin provides compensation for the control loop. |
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FB |
3 |
Feedback pin. The output voltage should be adjusted using a |
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resistor divider to provide 1.26V at this pin. |
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AGND |
4 |
Analog ground pin. |
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PGND |
5 |
Power ground pin. |
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DR |
6 |
Drive pin of the IC. The gate of the external MOSFET should be |
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connected to this pin. |
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FA/SD |
7 |
Frequency adjust and Shutdown pin. A resistor connected to this |
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pin sets the oscillator frequency. A high level on this pin for ≥ 30µs |
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will turn the device off. The device will then draw less than 10µA |
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from the supply. |
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VIN |
8 |
Power Supply Input pin. |
www.national.com |
2 |
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.
Input Voltage |
45V |
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FB Pin Voltage |
-0.4V < VFB < 7V |
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-0.4V < VFA/SD |
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FA/SD |
Pin Voltage |
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7V |
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Peak Driver Output Current (<10µs) |
1.0A |
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Power Dissipation |
Internally Limited |
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Storage Temperature Range |
−65˚C to +150˚C |
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Junction Temperature |
+150˚C |
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ESD Susceptibilty |
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Human Body Model (Note 2) |
2kV |
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Lead Temperature |
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MM Package |
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Vapor Phase (60 sec.) |
215˚C |
Infared (15 sec.) |
220˚C |
DR Pin Voltage |
−0.4V ≤ VDR ≤ 8V |
ISEN Pin Voltage |
500mV |
Operating Ratings (Note 1)
Supply Voltage |
2.97V ≤ VIN ≤ 40V |
Junction |
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Temperature Range |
−40˚C ≤ TJ ≤ +125˚C |
Switching Frequency |
100kHz ≤ FSW ≤ 1MHz |
Electrical Characteristics
Specifications in Standard type face are for TJ = 25˚C, and in bold type face apply over the full Operating Temperature Range. Unless otherwise specified, VIN = 12V, RFA = 40kΩ
Symbol |
Parameter |
Conditions |
Typical |
Limit |
Units |
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VFB |
Feedback Voltage |
VCOMP = 1.4V, |
1.26 |
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V |
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2.97 ≤ VIN ≤ 40V |
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1.2416/1.228 |
V(min) |
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1.2843/1.292 |
V(max) |
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∆VLINE |
Feedback Voltage |
2.97 ≤ VIN ≤ 40V |
0.001 |
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%/V |
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Line Regulation |
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∆VLOAD |
Output Voltage Load |
IEAO Source/Sink |
±0.5 |
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%/V (max) |
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Regulation |
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VUVLO |
Input Undervoltage |
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2.85 |
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V |
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Lock-out |
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2.97 |
V(max) |
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VUV(HYS) |
Input Undervoltage |
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170 |
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mV |
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Lock-out Hysteresis |
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130 |
mV (min) |
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210 |
mV (max) |
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Fnom |
Nominal Switching |
RFA = 40KΩ |
400 |
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kHz |
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Frequency |
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360 |
kHz(min) |
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430 |
kHz(max) |
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RDS1 (ON) |
Driver Switch On |
IDR = 0.2A, VIN= 5V |
16 |
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Ω |
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Resistance (top) |
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RDS2 (ON) |
Driver Switch On |
IDR = 0.2A |
4.5 |
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Ω |
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Resistance (bottom) |
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VDR (max) |
Maximum Drive |
VIN < 7.2V |
VIN |
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V |
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Voltage Swing(Note 6) |
VIN ≥ 7.2V |
7.2 |
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Dmax |
Maximum Duty |
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100 |
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% |
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Cycle(Note 7) |
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Tmin (on) |
Minimum On Time |
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325 |
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nsec |
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210 |
nsec(min) |
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600 |
nsec(max) |
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ISUPPLY |
Supply Current |
(Note 9) |
2.0 |
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mA |
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(switching) |
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3.0 |
mA (max) |
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IQ |
Quiescent Current in |
VFA/SYNC/SD = 5V (Note |
5 |
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µA |
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Shutdown Mode |
10), VIN = 5V |
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10 |
µA (max) |
VSENSE |
Current Sense |
VIN = 5V |
165 |
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mV |
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Threshold Voltage |
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140/ 135 |
mV (min) |
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195/ 200 |
mV (max) |
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LM3478
3 |
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LM3478
Electrical Characteristics (Continued)
Specifications in Standard type face are for TJ = 25˚C, and in bold type face apply over the full Operating Temperature Range. Unless otherwise specified, VIN = 12V, RFA = 40kΩ
Symbol |
Parameter |
Conditions |
Typical |
Limit |
Units |
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VSC |
Short-Circuit Current |
VIN = 5V |
325 |
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mV |
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Limit Sense Voltage |
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235 |
mV (min) |
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395 |
mV (max) |
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VSL |
Internal Compensation |
VIN = 5V |
92 |
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mV |
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Ramp Voltage |
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52 |
mV(min) |
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132 |
mV(max) |
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VOVP |
Output Over-voltage |
VCOMP = 1.4V |
50 |
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mV |
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Protection (with |
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32/ 25 |
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mV(min) |
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respect to feedback |
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78/ 85 |
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mV(max) |
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voltage) (Note 8) |
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VOVP(HYS) |
Output Over-Voltage |
VCOMP = 1.4V |
60 |
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mV |
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Protection |
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20 |
mV(min) |
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Hysteresis(Note 8) |
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110 |
mV(max) |
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Gm |
Error Ampifier |
VCOMP = 1.4V |
800 |
600/ 365 |
µmho |
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Transconductance |
IEAO = 100µA |
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µmho (min) |
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1000/ 1265 |
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(Source/Sink) |
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µmho (max) |
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AVOL |
Error Amplifier Voltage |
VCOMP = 1.4V |
38 |
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V/V |
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Gain |
IEAO = 100µA |
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26 |
V/V (min) |
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(Source/Sink) |
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44 |
V/V (max) |
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IEAO |
Error Amplifier Output |
Source, VCOMP = 1.4V, |
110 |
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µA |
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Current (Source/ Sink) |
VFB = 0V |
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80/ 50 |
µA (min) |
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140/ 180 |
µA (max) |
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Sink, VCOMP = 1.4V, VFB |
−140 |
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µA |
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= 1.4V |
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−100/ −85 |
µA (min) |
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−180/ −185 |
µA (max) |
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VEAO |
Error Amplifier Output |
Upper Limit |
2.2 |
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V |
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Voltage Swing |
VFB = 0V |
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1.8 |
V(min) |
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COMP Pin = Floating |
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2.4 |
V(max) |
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Lower Limit |
0.56 |
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V |
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VFB = 1.4V |
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0.2 |
V(min) |
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1.0 |
V(max) |
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TSS |
Internal Soft-Start |
VFB = 1.2V, VCOMP = |
4 |
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msec |
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Delay |
Floating |
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Tr |
Drive Pin Rise Time |
Cgs = 3000pf, VDR = 0 to |
25 |
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ns |
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3V |
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Tf |
Drive Pin Fall Time |
Cgs = 3000pf, VDR = 0 to |
25 |
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ns |
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3V |
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VSD |
Shutdown threshold |
Output = High |
1.27 |
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V |
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(Note 5) |
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1.35 |
V (max) |
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Output = Low |
0.65 |
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V |
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0.35 |
V (min) |
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ISD |
Shutdown Pin Current |
VSD = 5V |
−1 |
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µA |
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VSD = 0V |
+1 |
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TSD |
Thermal Shutdown |
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165 |
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˚C |
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Tsh |
Thermal Shutdown |
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10 |
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˚C |
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Hysteresis |
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θJA |
Thermal Resistance |
MM Package |
200 |
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˚C/W |
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4 |
Electrical Characteristics (Continued)
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: The human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin.
Note 3: All limits are guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).
Note 4: Typical numbers are at 25˚C and represent the most likely norm.
Note 5: The FA/SD pin should be pulled to VIN through a resistor to turn the regulator off. The voltage on the FA/SD pin must be above the maximum limit for Output = High to keep the regulator off and must be below the limit for Output = Low to keep the regulator on.
Note 6: The voltage on the drive pin, VDR is equal to the input voltage when input voltage is less than 7.2V. VDR is equal to 7.2V when the input voltage is greater than or equal to 7.2V.
Note 7: The limits for the maximum duty cycle can not be specified since the part does not permit less than 100% maximum duty cycle operation.
Note 8: The over-voltage protection is specified with respect to the feedback voltage. This is because the over-voltage protection tracks the feedback voltage. The overvoltage protection threshold is given by adding the feedback voltage, VFB to the over-voltage protection specification.
Note 9: For this test, the FA/SD pin is pulled to ground using a 40K resistor.
Note 10: For this test, the FA/SD pin is pulled to 5V using a 40K resistor.
Typical Performance Characteristics Unless otherwise specified, VIN = 12V, TJ = 25˚C.
IQ vs Input Voltage (Shutdown) |
ISupply vs Input Voltage (Non-Switching) |
10135534
|
10135503 |
ISupply vs VIN (Switching) |
Switching Frequency vs RFA |
10135535
10135504
LM3478
5 |
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LM3478
Typical Performance Characteristics Unless otherwise specified, VIN = 12V, TJ = 25˚C. (Continued)
Frequency vs Temperature |
Drive Voltage vs Input Voltage |
10135554 10135505
Current Sense Threshold vs Input Voltage COMP Pin Voltage vs Load Current
10135545 |
10135562 |
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Efficiency vs Load Current (3.3V In and 12V Out) |
Efficiency vs Load Current (5V In and 12V Out) |
10135559 |
10135558 |
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6 |
Typical Performance Characteristics Unless otherwise specified, VIN = 12V, TJ = 25˚C. (Continued)
Efficiency vs Load Current (9V In and 12V Out) |
Efficiency vs Load Current (3.3V In and 5V Out |
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10135560 |
10135553 |
Error Amplifier Gain |
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Error Amplifier Phase |
10135555 10135556
COMP Pin Source Current vs Temperature Short Circuit Sense Voltage vs Input Voltage
10135557
10135536
LM3478
7 |
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