Angular - how to show tooltip (ng-boostrap) when validation error

Question

I have reactive form with 2 fields: name and address

constructor(private fb: FormBuilder) {
  this.empForm = this.fb.group({
      name: ['', Validators.required],
      address: ''
  });
}

Htmp Template:

<form [formGroup]="empForm" novalidate>
    <input class="form-control" formControlName="name" [ngbTooltip]="tipContent" #t="ngbTooltip" triggers="manual">
    <input class="form-control" formControlName="address">
</form>

I want to show the tooltip when the input is not valid. How can I do that?