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MAX15021 Datasheet(PDF) 10 Page - Maxim Integrated Products |
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MAX15021 Datasheet(HTML) 10 Page - Maxim Integrated Products |
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10 / 24 page  Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability MAX15021 10 Maxim Integrated Detailed Description The MAX15021 incorporates dual-output, PWM, step- down, DC-DC regulators with tracking and sequencing options. The device operates over the input-voltage range of 2.5V to 5.5V. Each PWM regulator provides an adjustable output down to 0.6V and delivers up to 4A (regulator 1) and 2A (regulator 2) of load current. The high switching frequency (up to 4MHz) and integrated power switches optimize the MAX15021 for high-perfor- mance and small-size power management solutions. Each of the MAX15021 PWM regulator sections utilizes a voltage-mode control scheme for good noise immuni- ty and offers external compensation allowing for maxi- mum flexibility with a wide selection of inductor values and capacitor types. The device operates at a fixed switching frequency that is programmable from 500kHz to 4MHz with a single resistor. Operating the regulators with 180° out-of-phase clocking, and at frequencies up to 4MHz, significantly reduces the RMS input ripple current. The resulting peak input current reduction (and increase in the ripple frequency) significantly reduces the required amount of input bypass capacitance. The MAX15021 provides coincident tracking, ratiomet- ric tracking, or sequencing to allow tailoring of power- up/power-down sequence depending on the system requirements. When sequencing, it powers up glitch- free into a prebiased output. The MAX15021 includes internal undervoltage lockout with hysteresis, digital soft-start/soft-stop for “glitch-free” power-up and power-down. Protection features include lossless, cycle-by-cycle current limit, hiccup-mode out- put short-circuit protection, and thermal shutdown. Undervoltage Lockout (UVLO) The supply voltage (VAVIN) must exceed the default UVLO threshold before any operation starts. The UVLO circuitry keeps the MOSFET drivers, oscillator, and all the internal circuitry shut down to reduce current con- sumption. The UVLO rising threshold is 2.2V (typ) with a 120mV (typ) hysteresis. Digital Soft-Start/Soft-Stop The MAX15021 soft-start feature allows the load volt- age to ramp up in a controlled manner, eliminating out- put-voltage overshoot. Soft-start begins after VAVIN exceeds the undervoltage lockout threshold and the enable input is above 1.225V (typ). The soft-start cir- cuitry ramps up the reference voltage, controlling the rate of rise of the output voltage, and reducing input surge currents during startup. The soft-start duration is 4096 clock cycles. The output voltage is incremented through 64 equal steps. The output reaches regulation when soft-start is completed, regardless of the output capacitance and load. For tracking applications, soft-stop commences when the enable input falls below 1.1V (typ). The soft-stop circuitry ramps down the reference voltage controlling the output- voltage rate of fall. The output voltage is decremented through 64 equal steps in 4096 clock cycles. Oscillator Use an external resistor at RT to program the MAX15021 switching frequency from 500kHz to 4MHz. Calculate the appropriate resistor at RT for the desired output switching frequency (fSW): Tracking/Sequencing The MAX15021 features coincident/ratiometric tracking and sequencing (see Figure 1). Connect SEL to ground to configure the device as sequencer. Connect SEL to AVIN for tracking with output 1 as the master. Leave SEL unconnected for tracking with output 2 as the master. Assign the output with the higher voltage as the master. Rk A T[] . [] Ω= × × f [kHz] 1 [V] 4[MHz] SW 067 32 μ VOUT1 SOFT-START SOFT-START SOFT-START SOFT-STOP a) COINCIDENT TRACKING OUTPUTS b) RATIOMETRIC TRACKING OUTPUTS c) SEQUENCED OUTPUTS SOFT-STOP SOFT-STOP VOUT2 VOUT1 VOUT2 VOUT1 VOUT2 Figure 1. Graphical Representation of Coincident Tracking, Ratiometric Tracking, and Sequencing |
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