SNVS684D November 2010 – March 2016
The LM2936Q ultralow quiescent current regulator is ideally suited for automotive and other battery operated systems, with less than 15 μA quiescent current at a 100-μA load. The device features low dropout voltage and low current in the standby mode and retains all of the features that are common to low dropout regulators including a low dropout PNP pass device, short circuit protection, reverse battery input protection, and thermal shutdown. The LM2936Q has a 40-V maximum operating voltage limit and ±3% output voltage tolerance over the entire output current, input voltage, and temperature range.
Unlike many other PNP low dropout regulators, the LM2936Q remains fully operational with VIN = 40 V, and the LM2936QHBM remains fully operational with VIN = 60 V. Owing to power dissipation characteristics of the available packages, full output current cannot be ensured for all combinations of ambient temperature and input voltage.
While the LM2936QHBM maintains regulation to 60 V, it does not withstand a short circuit to ground on the output when VIN is above 40 V because of safe operating area limitations in the internal PNP pass device. Above 60 V the LM2936Q breaks down with catastrophic effects on the regulator and possibly the load as well. Do not use this device in a design where the input operating voltage may exceed 40 V, or where transients are likely to exceed 60 V.
The TSD circuitry of the LM2936Q has been designed to protect the device against temporary thermal overload conditions. The TSD circuitry is not intended to replace proper heat-sinking. Continuously running the LM2936Q device at TSD may degrade device reliability as the junction temperature will be exceeding the absolute maximum junction temperature rating. If the LM2936Q goes into TSD mode, the output current shuts off until the junction temperature falls approximately 10°C — the output current is then automatically restored. The LM2936Q continuously cycles in and out of TSD until the condition is corrected. The LM2936Q TSD junction temperature is typically 160°C.
The output current limiting circuitry of the LM2936Q has been designed to limit the output current in cases where the load impedance is unusually low. This includes situations where the output may be shorted directly to ground. Continuous operation of the LM2936Q at the current limit typically results in the LM2936Q transitioning into TSD mode.
The 5-V LM2936QHBMA has a pin for shutting down the regulator output. Applying a logic level high (> 2 V) to the SD pin causes the output to turn off. Leaving the SD pin open, connecting it to ground, or applying a logic level low (< 0.6 V) allows the regulator output to turn on.
The LM2936Q design does not include any undervoltage lockout (UVLO), or overvoltage shutdown (OVSD) functions. Generally, the output voltage tracks the input voltage until the input voltage is greater than VOUT + 1 V. When the input voltage is greater than VOUT + 1 V the LM2936Q is in linear operation, and the output voltage is regulated; however, the device is sensitive to any small perturbation of the input voltage. Device dynamic performance is improved when the input voltage is at least 2 V greater than the output voltage.