MAX8867EZK28+T

FAQFrequently Asked Questions

• What are the key design constraints when using the MAX8867EZK28+T in a battery-powered application with a 3.3V or 5V source? The MAX8867EZK28+T is a fixed 2.8V linear regulator with a maximum input voltage of 6.5V and typical dropout voltage of 0.165V at 150mA. For a 3.3V input, the regulator can reliably supply 2.8V at full current; however, with a 5V source, thermal dissipation becomes a consideration due to the 2.2V headroom. The quiescent current is 180µA, which affects standby power in battery applications. When selecting the MAX8867EZK28+T for portable devices, verify that your input supply remains below 6.5V absolute maximum to avoid damaging the device and exceeding the thermal budget of the TSOT-23-5 package.
• Can the MAX8867EZK28+T replace a standard 3.3V regulator in existing designs, and what design changes would be necessary? The MAX8867EZK28+T outputs a fixed 2.8V, not 3.3V, so it cannot serve as a direct replacement for 3.3V regulators without modifying circuit topology or component selection. If your application requires 2.8V rails for logic or analog circuits, the MAX8867EZK28+T may be suitable; otherwise, consider alternatives such as the MAX8864 (adjustable output) or other fixed-output variants in the Maxim Integrated series. The MAX8867EZK28+T does offer integrated over-current, over-temperature, reverse-polarity, and short-circuit protection, which may simplify your design compared to older fixed-output regulators lacking these features.
• How does the MAX8867EZK28+T perform under short-circuit conditions, and what precautions should be taken in the PCB layout? The MAX8867EZK28+T includes integrated short-circuit protection that limits output current during a fault. However, the regulator will dissipate power equal to (Vin − 2.8V) × 150mA under sustained short-circuit, potentially causing thermal shutdown. Adequate PCB thermal design is recommended; place the MAX8867EZK28+T on an internal ground plane and consider a small thermal via pattern beneath the device to improve heat dissipation in the TSOT-23-5 package. Enable the device using the control pin to allow software-based power sequencing and recovery from faults without manual reset.
• What is the impact of input voltage ripple on the MAX8867EZK28+T output stability, and what filtering is recommended upstream? The MAX8867EZK28+T specifies a PSRR (Power Supply Rejection Ratio) of 63dB at 10kHz, meaning high-frequency noise on the input is attenuated by roughly 1000:1. For a 100mV ripple at 10kHz on the input, the output ripple would be approximately 0.1mV. However, at lower frequencies (below 1kHz), the PSRR is reduced, so ripple rejection is less effective. A 1µF to 10µF ceramic capacitor on the input of the MAX8867EZK28+T is typically sufficient for filtering switching-mode supply noise; if sourcing from a noisy 5V rail, consider a larger bulk capacitor (10–47µF) upstream to reduce low-frequency ripple before the regulator input.
• Can the MAX8867EZK28+T be used in a multi-rail power sequencing application, and how should the enable pin be controlled? The MAX8867EZK28+T includes an active-high enable pin, allowing logic-level control of regulator shutdown. Multiple MAX8867EZK28+T devices can be enabled sequentially by a power-management IC or microcontroller to ensure ordered power-up of different voltage domains. Ensure the enable pin is pulled low through a 100kΩ resistor to ground if not actively driven, to prevent accidental enable during power ramp. The MAX8867EZK28+T will respond to enable transitions within microseconds, making it suitable for dynamic power gating in low-power applications.
• What are the thermal limitations of the MAX8867EZK28+T in the TSOT-23-5 package when operating continuously at 150mA? The MAX8867EZK28+T in TSOT-23-5 has limited thermal capacity; thermal dissipation is calculated as P = (Vin − 2.8V) × Iout. At a 5V input and 150mA output, the regulator dissipates approximately 330mW, which can raise the junction temperature significantly without adequate PCB thermal design. The operating temperature range is −40°C to 85°C (TA). Continuous operation near the upper temperature limit may trigger over-temperature shutdown. For applications requiring sustained 150mA at high input voltages (above 4V), verify that the regulator stays below 85°C junction temperature; if not, consider a lower-dropout or switching regulator alternative.
• How does the reverse-polarity protection in the MAX8867EZK28+T function, and are external components required? The MAX8867EZK28+T includes integrated reverse-polarity protection via an internal series element or diode that blocks reverse current. This protection prevents damage if the input supply is accidentally connected with reversed polarity; however, the MAX8867EZK28+T will not regulate during reverse-bias conditions. No external protective diode is required on the input for basic reverse-polarity protection, but a ferrite bead or small resistor in series with the input may be added to reduce EMI coupling without affecting performance. Verify input supply polarity before assembly to ensure normal operation.
• What output capacitance is recommended for stable operation of the MAX8867EZK28+T, and how sensitive is the regulator to ESR variations? A 1µF to 10µF ceramic output capacitor is typical for the MAX8867EZK28+T; this value stabilizes the feedback loop and reduces output noise. Ceramic capacitors (X7R or X5R) with low equivalent series resistance (ESR) are preferred to minimize transient overshoot during load steps. The MAX8867EZK28+T is relatively insensitive to moderate ESR variations, but excessively high ESR (>10Ω) may cause ringing or instability. Avoid using electrolytic capacitors alone on the output, as their high ESR can degrade transient response; use a 10µF ceramic in parallel with a larger bulk capacitor if needed for charge storage.
• Is the MAX8867EZK28+T suitable for noise-sensitive applications such as audio or RF circuits, and what precautions apply? The MAX8867EZK28+T offers 63dB PSRR at 10kHz, which provides reasonable noise rejection for many applications; however, for extremely noise-sensitive circuits (audio pre-amplifiers, RF front-ends), a linear regulator with higher PSRR or a dedicated low-noise variant may be preferable. The MAX8867EZK28+T's quiescent current of 180µA contributes low bias-current noise, but its output impedance at very high frequencies (above 100kHz) is less well-specified. For RF or audio designs, consider adding an RC low-pass filter (R = 10–100Ω, C = 10–100µF) on the MAX8867EZK28+T output to further attenuate broadband noise and switch-mode noise from upstream supplies.
• How does the MAX8867EZK28+T compare to adjustable-output regulators in terms of circuit complexity and cost trade-offs? The MAX8867EZK28+T is a fixed-output device, eliminating the need for external resistor dividers to set the output voltage; this reduces component count and PCB area compared to adjustable regulators like the MAX8864. However, fixed-output regulators offer no flexibility if multiple voltage levels are required. The MAX8867EZK28+T is typically lower cost than adjustable alternatives due to its simpler silicon design, but if your design requires multiple fixed outputs (e.g., 2.8V and 3.3V), two instances of the MAX8867EZK28+T or a single adjustable regulator may be more cost-effective depending on integration and board space constraints.
• What supply-current budget should be allocated for the MAX8867EZK28+T in a system power calculation? The MAX8867EZK28+T has a quiescent current (Iq) of 180µA and a maximum supply current specification of 100µA for control circuitry. In normal operation, the total input current is the sum of the output current (up to 150mA) plus the quiescent current. In shutdown (enable pin low), the regulator draws negligible current, typically in the low microampere range. For battery-powered designs, budget 180µA as the standby power drain when the MAX8867EZK28+T is active with no load; this contributes to sleep-mode power consumption and should be factored into battery life calculations for portable applications.
• Are there moisture or assembly concerns specific to the MAX8867EZK28+T TSOT-23-5 package? The MAX8867EZK28+T carries a Moisture Sensitivity Level (MSL) of 1, indicating unlimited floor-life tolerance; this means the device can be stored at room temperature and humidity without requiring desiccant packaging or baking before reflow. The TSOT-23-5 package is RoHS3 compliant and REACH unaffected, suitable for consumer, industrial, and automotive applications with standard lead-free solder processes. Standard reflow profiles (peak temperature 260°C) are compatible with the MAX8867EZK28+T; no special assembly precautions beyond normal SMT procedures are required.