Datasheet ADP1821 (Analog Devices) - 6

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ADP1821 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS BST 1 16 PVCC DH 2 15 DL SW 3 ADP1821 14 PGND SYNC 4 TOP VIEW 13 CSL (Not to Scale) FREQ 5 12 VCC SHDN 6 11 COMP PWGD 7 10 FB
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GND 8 9 SS
00 0- 31 05 Figure 4. Pin Configuration
Table 3. Pin Function Descriptions Pin No. Mnemonic Description
1 BST High-Side Gate Driver Boost Capacitor Input. A capacitor between SW and BST powers the high-side gate driver, DH. The capacitor is charged through a diode from PVCC when the low-side MOSFET is on. Connect a 0.1 μF or greater ceramic capacitor from BST to SW and a Schottky diode from PVCC to BST to power the high-side gate driver. 2 DH High-Side Gate Driver Output. Connect DH to the gate of the external high-side, N-channel MOSFET switch. DH is powered from the capacitor between SW and BST, and its voltage swings between VSW and VBST. 3 SW Power Switch Node. Connect the source of the high-side, N-channel MOSFET switch and the drain of the low-side, N-channel MOSFET synchronous rectifier to SW. SW powers the output through the output LC filter. 4 SYNC Frequency Synchronization Input. Drive SYNC with an external 300 kHz to 1.2 MHz signal to synchronize the converter switching frequency to the applied signal. The maximum SYNC frequency is limited to 2 times the nominal internal frequency selected by FREQ. Do not leave SYNC unconnected; when not used, connect SYNC to GND. 5 FREQ Frequency Select Input. FREQ selects the converter switching frequency. Drive FREQ low to select 300 kHz, or high to select 600 kHz. Do not leave FREQ unconnected. 6 SHDN Active Low, DC-to-DC Shutdown Input. Drive SHDN high to turn on the converter and low to turn it off. Connect SHDN to VCC for automatic startup. 7 PWGD Open-Drain, Power-Good Output. PWGD sinks current to GND when the output voltage is above or below the regulation voltage. Connect a pull-up resistor from PWGD to VDD for a logical power-good indicator. 8 GND Analog Ground. Connect GND to PGND at a single point as close as possible to the internal circuitry (IC). 9 SS Soft Start Control Input. A capacitor from SS to GND controls the soft start period. When the output is overloaded, SS is discharged to prevent excessive input current while the output recovers. Connect a 1 nF capacitor to a 1 μF capacitor from SS to GND to set the soft start period. See the Soft Start section. 10 FB Voltage Feedback Input. Connect to a resistive voltage divider from the output to FB to set the output voltage. See the Setting the Output Voltage section. 11 COMP Compensation Node. Connect a resistor-capacitor network from COMP to FB to compensate the regulation control system. See the Compensation section. 12 VCC Internal Power Supply Input. VCC powers the internal circuitry. Bypass VCC to GND with a 0.1 μF or greater capacitor connected as close as possible to the IC. 13 CSL Low-Side Current Sense Input. Connect CSL to SW through a resistor to set the current limit. See the Setting the Current Limit section. 14 PGND Power Ground. Connect GND to PGND at a single point as close as possible to the IC. 15 DL Low-Side Gate Driver Output. Connect DL to the gate of the low-side, N-channel MOSFET synchronous rectifier. The DL voltage swings between PGND and PVCC. 16 PVCC Internal Gate Driver Power Supply Input. PVCC powers the low-side gate driver, DL. Bypass PVCC to PGND with a 1 μF or greater capacitor connected as close as possible to the IC. Rev. C | Page 6 of 24 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION SIMPLIFIED BLOCK DIAGRAM PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION SOFT START ERROR AMPLIFIER CURRENT-LIMIT SCHEME MOSFET DRIVERS INPUT VOLTAGE RANGE SETTING THE OUTPUT VOLTAGE SWITCHING FREQUENCY CONTROL AND SYNCHRONIZATION COMPENSATION POWER-GOOD INDICATOR THERMAL SHUTDOWN SHUTDOWN CONTROL APPLICATION INFORMATION SELECTING THE INPUT CAPACITOR OUTPUT LC FILTER SELECTING THE MOSFETS SETTING THE CURRENT LIMIT FEEDBACK VOLTAGE DIVIDER COMPENSATING THE VOLTAGE MODE BUCK REGULATOR Type II Compensator Type III Compensator SETTING THE SOFT START PERIOD PCB LAYOUT GUIDELINE RECOMMENDED COMPONENT MANUFACTURERS APPLICATION CIRCUITS OUTLINE DIMENSIONS ORDERING GUIDE