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Better battery-powered designs with the new 160 V MOTIX™ 3-phase gate driver IC (Part 2)

Better battery-powered designs with the new 160 V MOTIX™ 3-phase gate driver IC (Part 2)

Srivatsa
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I remember a time when I was using a vacuum cleaner and accidentally overloaded it when a large object got stuck in the suction hose. The motor made a loud noise and then stopped working altogether. It turned out that the vacuum cleaner did not have any over current protection feature, which caused irreversible damage to the motor. That is when I realized the importance of such protection features in electronic devices. In part one of this blog series I introduced the new 6ED2742S01Q while today I will present to you 6ED2742S01Q's current sense amplifier & Itrip protection in typical applications such as power tools & vacuums.

The 6ED2742S01Q is a cost effective and easy-to-use gate driver IC for battery-powered applications. Its wide operating voltage range of 10 V to 120 V makes it the ideal “ONE” gate driver solution for a wide range of battery types like 12 V, 24 V, 48 V, 72, and 96 V. The 6ED2742S01Q is equipped with an over-current feature in addition to a stand-alone Current Sense Amplifier (CSA). These two robust protection and current sense schemes empower the system designer to implement reliable protection for the MOSFET inverter stage and current loop control. This article shows how.

Over current protection in 6ED2742S01Q

The over current protection functionality can sense over-current events in the DC-bus. Once the IC detects an over-current event, the outputs are shut down and RFE is pulled to VSS.

The level of current at which the over-current protection (OCP) is initiated is determined by the shunt resistor connected between COM pin and VSS pin as shown in Figure 1, and by the threshold configured by ITRIP CONF pin (VITRIP+). The circuit designer will need to determine the maximum allowable level of current in the DC-bus and select R0 and VITRIP+

VITRIP+ = R0 x IDC-


Figure 1.PNG

Figure 1. Programming the over-current protection

For example, a typical value for resistor R0 could be 10 mΩ, which gives an over current trip point of 13 A for the lowest threshold setting of 130 mV.

Current sense operational amplifier in 6ED2742S01Q

 A current sense operational amplifier (CSA) with configurable gain is integrated in the gate driver to sense the voltage between VSS and COM pins. The amplifier has a strobe input signal. When the strobe signal is “LOW”, the operational amplifier output signal CSO is following the VSS-COM voltage multiplied by a certain gain. When the strobe signal is “HIGH”, the CSO signal is reporting the op amp offset. CSO output has an offset added above VSS of 150 mV. This offset ensures the measured current remains positive and does not go negative in any regular operating conditions. This lets the microcontroller ADC work efficiently.

Figure 2.PNG

 Figure 2. Current sense operational amplifier and its timing diagram

Gain settings for the over current protection (ITRIP_Conf) and current sense operational amplifier (CSO)

The gain for the over current protection via ITRIP and current sense operation amplifier output can be set using a simple potential divider network as shown in below Figure 3.

Figure 3.PNG

Figure 3. Setting over current protection (ITRIP) gain and current sense operational amplifier gain via the resistor divider

The voltage of the potential divider network can be scaled down from an external 3.3 V. It should be noted that when powering from external 3.3 V, the supply sequencing should be such that the 6ED2742 is first powered up via VIN before applying the 3.3 V to the Gain/Config pins.

Two use cases are shown in Figure 5. “Fig a” shows the option where the 3.3 V input is either ramped up after or along with VIN / VCC. The RFE gets asserted (IC gets enabled) after the UVLO of VCC is crossed and the VRFE+ threshold is crossed. “Fig b” shows use case when the 3.3 V input is already available before VIN / VCC arrive. In this case, the RFE gets asserted when the UVLO of VCC is crossed.  It is good to note that the RFE pin is held low under two conditions:

  1. Under Voltage Lock Out (UVLO) of VCC / VRFE
  2. ITRIP threshold as set by ITRIP Config is crossed  

In case the 3.3 V arrives before VCC toggling (the pulling down and pulling up) the RFE will re-read the values of ITRIP config and CSO Gain.

Fig. A and Fig. B.PNG

 Figure 4. Input voltage sequencing for setting up different gain and ITRIP config

The voltage limits for different gains are as shown in Table 1 and Table 2 below.

Table 1. ITRIP Config pin voltage settings for different overcurrent threshold voltages

VITRIP

Over current threshold voltage

950

1000

1050

mV

ITRIP Conf > 3 V

475

500

525

1.5V < ITRIP Conf < 2V

225

250

275

0.5V < ITRIP Conf < 1V

110

130

150

ITRIP Conf < 0.25V

 

Table 2. CSO gain pin voltage settings for different gain of CSO output

GCSO

Current sense amplifier gain

36

40

41

 

 

V/V

CSO gain > 3 V

18

20

21

1.5V < CSO gain< 2V

9

10

11

0.5V < CSO gain < 1V

4

5

6

CSO gain < 0.25V

 

With the above basic analog (resistor-based) configurations to setup the over-current protection and current sense amplifier, the designer can also use DAC (digital to analog converter) within the microcontroller to dynamically set the threshold and gains and toggle the RFE to set the configuration for subsequent cycles.

These current sense amplifier and over current trip (Itrip) protection features of the 6ED2742S01Q provide the ideal solution for typical applications such as power tools and vacuum cleaners.    

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