link to page 16 link to page 16 link to page 16 link to page 16 link to page 16 LTM4653 PIN FUNCTIONS PGOOD (D1): Power Good Indicator, Open-Drain Output default loop compensation. Loop compensation (a series Pin. PGOOD is high impedance when PGDFB is within resistor-capacitor) can be applied externally to COMPa if approximately ±7.5% of 0.6V. PGOOD is pulled to GND desired or needed, instead. (See COMPb.) when PGDFB is outside this range. COMPb (E1): Internal Loop Compensation Network. For PGDFB (D2): Power Good Feedback Programming Pin. most applications, the internal, default loop compensation Connect PGDFB to VOSNS through a resistor, RPGDFB. of the LTM4653 is suitable to apply “as is”, and yields very RPGDFB configures the voltage threshold of VOUT for which satisfactory results: apply the default loop compensation to PGOOD toggles its state. If the PGOOD feature is used, the control loop by simply connecting COMPa to COMPb. set RPGDFB to: When more specialized applications require a personal ⎛ V ⎞ touch to the optimization of control loop response, this R OUT PGDFB = ⎜ – 1⎟ • 4.99k can be accomplished by connecting a series resistor-
⎝ 0.6V ⎠
capacitor network from COMPa to SGND—and leaving otherwise, leave PGDFB open circuit. COMPb open circuit. A small filter capacitor (220pF) internal to the LTM4653 VINREG (D3): Input Voltage Regulation Programming on this pin provides high frequency noise immunity for Pin. Optionally connect this pin to the midpoint node the PGOOD output indicator. formed by a resistor-divider between VD and SGND. When f the voltage on VINREG falls below approximately 2V, a SET (E3): Oscillator Frequency Programming Pin. The default switching frequency of the LTM4653 is 400kHz. VINREG control loop servos VOUT to decrease the power Often, it is necessary to increase the programmed fre- inductor current and thus regulate VINREG at 2V. (See quency by connecting a resistor between f the Applications Information section.) SET and SGND. (See the Applications Information section.) Note that the If this input voltage regulation feature is not desired, con- synchronization range of CLKIN is approximately ±40% nect VINREG to INTVCC. of the oscillator frequency programmed by the fSET pin. IMONa (C2): Power Inductor Current Analog Indicator Pin CLKIN (B1): Mode Select and Oscillator Synchronization and Current Limit Programming Pin. The current flowing Input. Leave CLKIN open circuit for forced continuous out of this pin is equal to 1/40,000 of the average power mode operation. Alternatively, this pin can be driven to inductor current. To construct a voltage (VIMONa) that is synchronize the switching frequency of the LTM4653 to proportional to the power inductor current, optionally a clock signal. In this condition, the LTM4653 operates apply a parallel resistor-capacitor network to this pin and in forced continuous mode and the cycle-by-cycle turn- terminate it to SGND. on of the primary power MOSFET MT is coincident with the rising edge of the clock applied to CLKIN. Note the IMONa can be connected to IMONb if the default resis- synchronization range of CLKIN is approximately ±40% tor-capacitor termination network provided by IMONb is of the oscillator frequency programmed by the f desired: 1V at full scale (4A) load current. (See IMONb.) SET pin. (See the Applications Information section.) If this analog indicator feature is not desired, connect IMONa to SGND. COMPa (E2): Current Control Threshold and Error Ampli- fier Compensation Node. The trip threshold of LTM4653’s If IMONa ever exceeds a trip threshold of approximately current comparator increases with a corresponding rise 2V, an IMON control loop servos VOUT to decrease power in COMPa voltage. A small filter cap (10pF) internal to the inductor current and thus regulate IMONa at 2V. In this LTM4653 on this pin introduces a high-frequency roll- manner, the average current limit inception threshold of off of the error-amplifier response, yielding good noise the LTM4653 can be configured. (See the Applications rejection in the control-loop. COMPa is often electrically Information section.) connected to COMPb in one’s application, thus applying Rev 0 For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Test Circuit Decoupling Requirements Operation Operation Operation Applications Information Typical Applications Package Photograph Package Description Typical Application Related Parts
