Datasheet ADP1870, ADP1871 (Analog Devices)

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Synchronous Buck Control er with Constant On-Time and Val ey Current Mode Data Sheet ADP1870/ ADP1871 FEATURES TYPICAL APPLICATIONS CIRCUIT Power input voltage range: 2.95 V to 20 V VIN = 2.95V TO 20V On-board bias regulator Minimum output voltage: 0.6 V VIN CC ADP1870/ 0.6 V reference voltage with ±1.0% accuracy C C C2 IN RC ADP1871 Supports all N-channel MOSFET power stages RTOP COMP/EN BST VOUT CBST Q1 Available in 300 kHz, 600 kHz, and 1.0 MHz options L FB DRVH VOUT No current-sense resistor required RBOT GND SW COUT Power saving mode (PSM) for light loads (ADP1871 only) C Q2 VREG2 VREG DRVL Resistor-programmable current-sense gain PGND RRES LOAD Thermal overload protection C
001
VREG Short-circuit protection
08730-
Precision enable input
Figure 1.
Integrated bootstrap diode for high-side drive Starts into a precharged load 100 V Small, 10-lead MSOP and LFCSP packages 95 IN = 5V (PSM) 90 APPLICATIONS 85 80 Telecom and networking systems 75 %) Mid to high end servers ( 70 VIN = 16.5V Set-top boxes 65 NCY E 60 VIN = 13V DSP core power supplies ICI F 55 V F IN = 13V (PSM) 12 V input POL supplies E 50 TA = 25°C V 45 OUT = 1.8V fSW = 300kHz 40 VIN = 16.5V (PSM) GENERAL DESCRIPTION WÜRTH INDUCTOR: 35 744325120, L = 1.2µH, DCR = 1.8mΩ 30 INFINEON FETs:
The ADP1870/ADP1871 are versatile current-mode, synchronous
BSC042N03MS G (UPPER/LOWER) 25
step-down control ers that provide superior transient response,
10 100 1k 10k 100k
102
LOAD CURRENT (mA)
optimal stability, and current-limit protection by using a constant 08730- Figure 2. Efficiency vs. Load Current (V on-time, pseudo-fixed frequency with a programmable current- OUT = 1.8 V, 300 kHz) limit, current-control scheme. In addition, these devices offer optimum performance at low duty cycles by utilizing valley In addition, an internal y fixed soft start period is included to limit current-mode control architecture. This allows the ADP1870/ input in-rush current from the input supply during startup and ADP1871 to drive al N-channel power stages to regulate output to provide reverse current protection during soft start for a pre- voltages as low as 0.6 V. charged output. The low-side current-sense, current-gain scheme The ADP1871 is the power saving mode (PSM) version of the and integration of a boost diode, along with the PSM/forced pulse- device and is capable of pulse skipping to maintain output width modulation (PWM) option, reduce the external part count regulation while achieving improved system efficiency at light and improve efficiency. loads (see the Power Saving Mode (PSM) Version (ADP1871) The ADP1870/ADP1871 operate over the −40°C to +125°C section for more information). junction temperature range and are available in a 10-lead MSOP Available in three frequency options (300 kHz, 600 kHz, and and LFCSP packages. 1.0 MHz, plus the PSM option), the ADP1870/ADP1871 are well suited for a wide range of applications that require a single-input power supply range from 2.95 V to 20 V. Low voltage biasing is supplied via a 5 V internal LDO.
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Document Outline Features Applications General Description Typical Applications Circuit Revision History Specifications Absolute Maximum Ratings Thermal Resistance Boundary Condition ESD Caution Pin Configuration and Function Descriptions Typical Performance Characteristics ADP1870/ADP1871 Block Diagram Theory of Operation Startup Soft Start Precision Enable Circuitry Undervoltage Lockout On-Board Low Dropout Regulator Thermal Shutdown Programming Resistor (RES) Detect Circuit Valley Current-Limit Setting Hiccup Mode During Short Circuit Synchronous Rectifier Power Saving Mode (PSM) Version (ADP1871) Timer Operation Pseudo-Fixed Frequency Applications Information Feedback Resistor Divider Inductor Selection Output Ripple Voltage (ΔVRR) Output Capacitor Selection Compensation Network Output Filter Impedance (ZFILT) Error Amplifier Output Impedance (ZCOMP) Error Amplifier Gain (GM) Current-Sense Loop Gain (GCS) Crossover Frequency Efficiency Considerations Channel Conduction Loss MOSFET Driver Loss Switching Loss Diode Conduction Loss Inductor Loss Input Capacitor Selection Thermal Considerations Design Example Input Capacitor Inductor Current Limit Programming Output Capacitor Feedback Resistor Network Setup Compensation Network Loss Calculations External Component Recommendations Layout Considerations IC Section (Left Side of Evaluation Board) Power Section Differential Sensing Typical Applications Circuits 15 A, 300 kHz High Current Application Circuit 5.5 V Input, 600 kHz Application Circuit 300 kHz High Current Application Circuit Outline Dimensions Ordering Guide