Article Directory
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- ▉ How to play 1: EN foot is floating
- ▉ How to play 2: Use CPU GPIO to control EN pin
- ▉ How to play 3: EN pin is connected to VIN through two voltage divider resistors
- ▉ How to play 4: EN pin adjusts the UVLO threshold through two voltage dividers
- ▉ How to play 5: EN pin externally add RC delay circuit
- ▉ Gameplay 6: Multi-power cooperative combat
- ▉ More ways to play waiting for you to unlock
The power chip in this article refers to a DC-DC or LDO chip.
EN means enable, which means enable, which means that only when the pin is activated, the power chip will have output.
Designing different peripheral circuits on the EN pin can realize multiple power-on functions of the power chip. Regardless of a small EN pin, a poor design will also affect the normal operation of the power chip.
Let's take a look at the ways to play with EN pins!
▉ How to play 1: EN foot is floating
Some DC_DC EN pins support floating enable, which means that EN does not need to be connected to any device, as long as there is input, there will be output.
某些DC-DC的pin description里面有float to enable字样
Why can it be enabled even if it is left floating?
The DC-DC EN pin with float to enable has a built-in pull-up source connected to the input VIN. When the EN pin is floating, a 0.9uA pull-up source is used to turn on the power.
EN管脚的内部上拉源
▉ How to play 2: Use CPU GPIO to control EN pin
The DC-DC is turned on/off by outputting the high and low levels of the GPIO of the single-chip microcomputer. Generally, the EN pin has a threshold value. When this value is exceeded, the DC-DC is turned on, and the DC-DC is turned off below this value.
在电气参数栏可以查看DC-DC EN脚开启阈值电压
It is recommended to reserve two voltage divider resistors in the design to improve compatibility. It can be targeted when replacing CPUs with different IO voltages.
通过单片机的GPIO控制DC-DC EN pin
But also pay attention not to exceed the maximum withstand voltage of EN pin.
DC-DC EN管脚耐压最大值
▉ How to play 3: EN pin is connected to VIN through two voltage divider resistors
Someone said, I don’t use the GPIO control of the CPU. If I want to power on the DC-DC, there will be an output. You can connect two resistors through VIN to the EN pin. **This is more common in DC-DC chips, **General The VIN and EN voltages are not at the same level, and the higher VIN voltage needs to be divided, see the left figure below.
VIN and EN are at the same voltage level, which is more common in LDO chips , and can be pulled up to VIN through resistor R1, see the middle figure below.
Or VIN and EN are directly short-circuited and connected, and R1 is replaced by a wire. At this time, the power-on and relationship depend on the UVLO threshold of VIN input, as shown in the right figure below.
VIN通过分压电阻接到DC-DC EN pin
▉ How to play 4: EN pin adjusts the UVLO threshold through two voltage dividers
The advantage of connecting to the EN pin through a voltage divider resistor is that you can set the DC-DC start voltage and shutdown voltage. The Vstart and Vstop voltage values are at least higher than the DC-DC UVLO value, otherwise setting the voltage divider resistance is meaningless.
The full name of UVLO is under voltage lock out . As the name implies, it is low voltage lock out , that is, under voltage protection.
UVLO is for the input VIN of DC-DC. When the voltage is lower than a certain value, DC-DC directly locks and protects. UVLO limits the minimum input voltage of the power chip, which can ensure that the chip will not be unstable to a certain extent. Oscillation improves the stability and reliability of the power chip during operation.
The threshold of UVLO is usually less than the minimum input voltage value of VIN, and is controlled by the internal register of the chip. In some applications, if you do not want UVLO to be so low, you can set the power supply start voltage and stop by adjusting the resistance of the voltage divider. Voltage.
The calculation formula of r1 is: r 1 = V start − V stop I hys r1=\frac{Vstart-Vstop}{Ihys}r 1=I h y sV s t a r t−In the t of the p
The calculation formula of r2 is: r 2 = V ena V start − V enar 1 + I 1 r2=\frac{Vena}{\frac{Vstart-Vena}{r1}+I1}r 2=r 1V s t to r t - V e n to+I 1Vena
- Vstart is the start voltage, and Vstop is the shutdown voltage;
- Vena is the EN threshold voltage;
- Ihys is the hysteresis current, I1 is the EN pull-up source current;
- r1 and r2 are external divider resistors;
If the requirement is not high, you can directly use the formula: V start = V stop = V ena ∗ (r 1 + r 2) r 2 Vstart=Vstop=\frac{Vena*(r1+r2)}{r2}V s t a r t=V s t o p=r 2Vena∗( r 1+r 2 )
That is, the power supply above Vstart is turned on, and the power supply below Vstart is turned off.
In order to enable DC-DC stably, you can set Vena to be larger than its threshold (between the threshold and its maximum value). According to the threshold and the desired turn-on voltage, select the appropriate values of r1 and r2 .
▉ How to play 5: EN pin externally add RC delay circuit
Some circuits have multiple LDOs, and there are timing requirements for LDO power-on. At this time, you can add RC to EN Pin and set the size of RC to meet the requirements. If VOUT1 is required to be powered on before VOUT2, you can R1C1 parameter setting is smaller than R2C2.
上电时序有要求的可在EN Pin上加RC延时电路
The EN pin can also be used for two GPIO control, using the control delay of the two GPIOs to meet the timing requirements.
用两个GPIO控制EN来满足上电时序
In order to prevent the output voltage from being affected by the fluctuation of the input voltage (T1~T2) when the power is just turned on in some occasions, use a voltage divider resistor or RC delay circuit to make the input voltage rise to 70-80%*VIN, and then turn on the enable EN (After T2) to get a more stable output voltage.
Vout受到Vin电压波动的影响
▉ Gameplay 6: Multi-power cooperative combat
Some circuits use a variety of power, can be used for a power supply to pin PWRGD drive EN Pin under a power supply and meet bliss when in trouble with the object, i.e., on a power switch, a power supply under The upper-level power supply is abnormal, and the next-level power supply cannot be turned on (open and closed at the same time). This circuit can also meet the timing requirements, that is, VOUT2 is slower than VOUT1.
用上一级PWRGD管脚来驱动下一级电源的EN Pin
The PWRGD in the above figure is an open-drain output. When the power supply is abnormal, this pin will be pulled low to indicate whether the power supply is good.
PWRGD管脚描述
The following are the power-on waveforms of EN1, PWRGD1, VOUT1, and VOUT2. It can be seen that after the front-end power supply is fully powered up, that is, when the PWRGD1 pin becomes a stable high level, VOUT2 starts to rise slowly.
双电源EN1、PWRGD1、VOUT1、VOUT2上电波形
▉ More ways to play waiting for you to unlock
Introduced these 6 kinds of gameplay, you can draw inferences, and there are many EN pin design methods that are not listed one by one. The purpose of designing EN pins is to realize the corresponding functions and the stable and reliable operation of the power chip.
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