Features
GENERAL
| • | 4.5V to 30V input range |
| • | Power good function |
| • | Input under-voltage lockout |
| • | 10 µA Shutdown/Recycle for entire chip |
| • | Thermal shutdown |
| • | TSSOP package |
SWITCHING SECTION
| • | Two synchronous buck regulators for fixed 5V/3.3V or adjustable outputs |
| • | Outputs adjustable from 1.3V to 5.5V |
| • | 0.04% (typical) line and load regulation error |
| • | Selectable switching frequency 200/300 kHz |
| • | Two channels operating 180° out of phase |
| • | Separate on/off for each channel |
| • | Separate Power Good signals |
| • | Current mode control with or without sense resistor |
| • | Adjustable cycle-by-cycle current limit |
| • | Skip-mode operation available |
| • | Negative current limit |
| • | Separate soft start for each channel |
| • | Output UVP and OVP |
| • | Programmable output UVP delay |
| • | Self discharge of output capacitors when turned off |
LINEAR SECTION
| • | Adjustable (3.3V to 15V) linear regulator with external PNP pass transistor |
| • | ±2% initial tolerance of set voltage |
| • | Output UVP for adjustable linear regulator |
| • | Fixed 3.3V/50mA output rail |
| • | Fixed 5V reference rail |
Description The LM2645 is a feature-rich IC that combines two current mode synchronous buck regulator controllers, an adjustable linear regulator controller and a fixed 3.3V standby output rail.
The two switching regulator controllers operate 180° out of phase. This feature reduces the input ripple RMS current, thereby significantly reducing the required input capacitance. The two switching regulator outputs can also be paralleled to operate as a dual-phase regulator.
The use of synchronous rectification and pulse-skip operation at light load achieves high efficiency over a wide load range. Fixed-frequency operation can be obtained by disabling the pulse-skip mode. The switching frequency of the LM2645 is user selectable between 200 kHz or 300 kHz.
The first switching controller (Channel 1) features a fixed 5V output, and the second switching controller controller (Channel 2) features a fixed 3.3V output. Both channels can also be independently adjusted from 1.3 to 5.5V. The adjustable linear regulator can be adjusted from 3.3V to 15V. An internal 5V rail is also available externally for driving bootstrap circuitry. This rail also serves as the input for an internal LDO that provides the fixed 3.3V/50mA output rail.
Current-mode feedback control assures excellent line and load regulation and a wide loop bandwidth for excellent response to fast load transients. Current is sensed across either the Vds of the top FET or across an external sense resistor connected in series with the drain of the top FET. Current limit is independently adjustable for each channel.
The analog soft-start for the switching controllers uses an innovative new approach. It is independent of the input voltage which makes the soft-start behavior more predictable and controllable.
Independant PGOOD signals monitor each of the switching regulator outputs. The switching outputs have under-voltage and over-voltage latch protection, while the output of the external linear regulator has undervoltage latch protection. The undervoltage latch can be disabled or adjustably delayed.
Applications
| • | Notebook and sub-notebook computers |
| • | Embedded computer systems |
| • | Battery-powered instruments |
| • | High end gaming systems |
| • | Set-top boxes |
| • | WebPAD |
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