If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance. All information these cookies collect is aggregated and therefore anonymous. They help us to know which pages are the most and least popular and see how visitors move around the site. Performance Cookies: These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. If you do not allow these cookies then some or all of these services may not function properly. They may be set by us or by third party providers whose services we have added to our pages. Functional Cookies: These cookies enable the website to provide enhanced functionality and personalization. These cookies do not store any personally identifiable information. You can set your browser to block or alert you about these cookies, but some parts of the site will not then work. They are usually only set in response to actions made by you which amount to a request for services, such as setting your privacy preferences, logging in or filling in forms. Strictly Necessary Cookies: (Always Active) These cookies are necessary for the website to function and cannot be switched off in our systems. After we finish updating our website, you will be able to set your cookie preferences. This example uses the IRF7530 because of its low V GS (1.2V) and high current capability (5.4A).Īnalog Devices is in the process of updating our website. To ensure that the transistor fully turns on, select an nMOS that has a gate threshold voltage < 2.25V. This provides a V GS(ON) of 2.25V (4V - 1.75V). The DS2714 will stop charging a cell above 1.75V. That means that the output of the inverter, ideally, should be 4V when CCx is active. The inverter should be powered from the same supply as the DS2714, which has a minimum supply voltage of 4V. Transistor SelectionĬare must be taken when selecting an nMOS transistor to ensure that it can handle the charge current and will fully turn on within the application's voltage range. A diagram of an example application for the DS2714 that uses nMOS, instead of pnp, transistors. Because CCx pins are open drain, a pullup resistor needs to be added from V CC to CCx.įigure 1. The nMOS drain should be connected to V CHG, and the nMOS source should be connected to the battery. ConnectionĬonnect the output of your CCx pin to the input of an inverter then, connect the output of that inverter to the gate of an nMOS transistor. This application note provides an example that uses an inverter with nMOS transistors to avoid the problems associated with the pnp-transistor configuration. Depending on the charge rate, the base current (i b), can be close to the limit of the DS2714. The drawback of using a pnp transistor is that the IC has to sink a current proportional to the charge current (i b = β × i c). Having V CHG at V CELL will not generate a high enough V GS for a pMOS transistor to turn on. Since V CHG is a current-regulated supply, the voltage drops to ~V CELL when charging. This is the most efficient configuration for component count, but it is not necessarily the best for every application. The DS2714 application example in the datasheet uses pnp transistors to switch the charge current on and off.
#Vth nmos transistor how to
This application note describes how to use nMOS, instead of pnp, transistors to avoid this problem. This can be problematic because the current-sink capability of the charge control pins may restrict the charge current through the pnp transistor. The example circuit in the data sheet for the DS2714 stand-alone NiMH charger uses pnp transistors to switch the charge current on and off.
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