PDF SC416 Data sheet ( Hoja de datos )

Número de pieza	SC416
Descripción	Dual Synchronous Buck Controller
Fabricantes	Semtech Corporation
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SC416 POWER MANAGEMENT Features Dual Synchronous Buck Controller with Tracking Start-up/Shutdown Description VIN Range 3-25V Outputs Adjustable from 0.75 to 5.25V, or Preset Output Voltages: • VOUT1 = 1.8 or 1.5V • VOUT2 = 1.25 or 1.05V Proportional or Coincident Tracked Start-up and Shut- down of Both Outputs www.DataSheet4U.com Adjustable Soft-start Rates for Each Output Regulated Shutdown for Each Output Low Shutdown Power Constant On-Time for Fast Dynamic Response Adjustable Switching Frequency Separated Frequencies for Minimal Switching Interac- tion: • VOUT1 = up to 600kHz • VOUT2 = up to 720kHz Power Save or Continuous Operation at Light Load Over-Voltage and Under-Voltage Fault Protection Cycle-by-Cycle Valley Current Limit DC Current Sense Using Low-Side RDSON Sensing, or RSENSE In Source of Low-Side MOSFET for Greater Accuracy Separate Power Good Outputs Separate Enable/Power Save Inputs 3.1A Non-Overlapping Gate Drive SmartDriveTM for High-side MOSFET MLP 4x4 24 Pin Lead-free Package Industrial Temperature Range WEEE and RoHS Compliant Applications Notebook and Sub-Notebook Graphics Voltage Controllers Tablet PCs Embedded Applications The SC416 is a versatile, constant on-time, pseudo- fixed-frequency, dual synchronous buck PWM control- ler intended for notebook computers and other battery operated portable devices. The SC416 contains all the features needed to provide cost-effective control of two independent switchmode power supplies. The SC416 provides adjustable voltage tracking during start-up and shut-down, making it an effective solution for a variety of applications where the voltage differen- tial between supply rails must meet defined limits dur- ing all operating conditions including start-up and shut- down. The SC416 supports proportional tracking which gives equal start-up and shut-down times for both out- puts, and can also provide coincident tracking where the two output voltages are equal during the lower voltage’s start-up and shut-down ramp. The two DC outputs are adjustable from 0.75V to 5.25V. Additional features for each output include cycle-by- cycle current limit, voltage soft-start, under-voltage and over-voltage protection, programmable over-current protection, regulated shutdown, selectable power save and non-overlapping gate drive. The SC416 provides two enable/power save inputs, two soft-start inputs, two power good outputs and an on-time adjust input. The constant on-time topology provides fast dynamic response. The excellent transient response means that SC416 based solutions require less output capacitance than competing fixed frequency converters. Switching frequency is constant until a step in load or line voltage occurs, at which time the pulse density and frequency moves to counter the change in output voltage. After the transient event, the controller frequency returns to steady state operation. At light loads with power save enabled, the SC416 reduces switching frequency for im- proved efficiency. May 17, 2007 © 2007 Semtech Corporation 1 1 page SC416 Electrical Characteristics (continued) Parameter Regulation (Continued) VOUT2 On-Time Threshold www.DataSVhOeeUtT4xUL.cinome Regulation Error VOUTx Load Regulation Error Timing VOUTx On-Time(1) VOUTx Set to 1.5V Minimum On-Time Minimum Off-Time Soft-Start/Shutdown Soft-Start SSx Current Source Shutdown SSx Current Sink Soft-Start Ramp Time SSx Shutdown Discharge Resistance VOUTx Shutdown Discharge Resistance Analog Inputs/Outputs VOUT1 Input Resistance VOUT2 Input Resistance FBx Input Bias Current Current Sense ILIMx Source Current ILIMx Comparator Offset Current Limit (Negative) Zero Crossing Detector Threshold Power Good PGDx Threshold PGDx Threshold Delay Time (2) Conditions FB2 = 5V; 0 to 85°C FB2 = 5V; -40 to 85°C FB2 = RTN; 0 to 85°C FB2 = RTN; -40 to 85°C VOUT1; RTON = 1Meg VOUT2; RTON = 1Meg VOUT1; RTON = 499K VOUT2; RTON = 499K DH1, DH2 DL1, DL2 CSSx = 4.7nF ENx = RTN, VOUTx < 300mV ENx = RTN, VOUTx < 300mV EN1 = VDD1 EN2 = VDD2 ILIMx - GND LXx - GND LXx - GND 1% Hysteresis Typical, with Respect to Regulation Point 25°C Min Typ Max -40° to 85°C Min Max Units 1.25 1.2343 1.2656 V 1.25 1.2281 1.2718 1.05 1.0368 1.0631 1.05 1.0316 1.0684 V 0.04 %/V 0.3 % 400 320 480 330 260 400 nsec 200 167 50 ns 330 ns 5 3.5 6.5 μA 5 3.5 6.5 μA 700 μsec 16 Ω 16 Ω 120 kΩ 90 kΩ -1 +1 μA 10 9 11 μA -10 +10 mV 80 60 100 mV -7 +7 mV -12 -9 -15 % 5 μs 5 5 Page SC416 Applications Information (continued) Enable/Psave Inputs Each converter has a separate Enable pin. Each EN input operates as follows: EN = GND. This turns the converter off. EN = open (float). This turns the converter on with psave mode disabled (continuous conduction mode). In this case, the EN pin will float to approximately 2V due to www.DataSheet4U.com an internal 1.5Meg/1Meg resistor divider from +5V to ground. EN = high (3.1V min). This turns the converter on with psave mode enabled. At light loads, the converter will operate in psave mode. Note that the two EN pins are separate, so each output can be disabled or operated with or without psave inde- pendently. immediately exits Psave. Once Psave is exited, it requires 8 switching cycles at light load to re-enter psave. Since the controller counts zero crossings, the converter can sink current as long as the current does not cross zero on eight consecutive cycles. This allows the output voltage to recover quickly in response to negative load steps. When operating in Psave mode at light loads, the LX waveform will not have the typical square wave shape seen when operating in continuous conduction mode. Shortly after DL drives low, and both MOSFETs are off, the LX voltage will show ringing. This ringing is caused by the LC circuit formed by the inductor and device ca- pacitance of the MOSFETs and low-side diode. When the low-side MOSFET turns off the inductor current falls toward zero. When it reaches zero, the inductance and MOSFET capacitances will tend to ring freely. This is nor- mal Psave operation as shown in Figure 3. VIN For tracking operation during startup, the two EN pins are typically tied together; see the Voltage Tracking sec- tion. DH Q1 CQ1 L VOUT If both EN1 and EN2 are grounded, the device is placed into the lowest-power state, drawing typically 7μA from the +5V supply. DL Q2 COUT CQ2 Psave Operation Each output provides automatic psave operation at light loads if the ENx pin is set high. The internal Zero-Cross comparator looks for inductor current (via the voltage across the lower MOSFET) to fall to zero on eight con- secutive switching cycles. Once observed, the control- ler enters psave mode and turns off the low-side MOS- FET on each subsequent cycle when the current crosses zero. To add hysteresis, the on-time is also increased by 25% in Psave, for that converter only; it does not affect the other converter’s on-time. The efficiency improve- ment at light loads more than offsets the disadvantage of slightly higher output ripple. If the inductor current does not cross zero on any switching cycle, the controller DL LX VIN VOUT Typical ringing at LX Figure 3 11 11 Page

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