Constant defined in header.php not visible in functions.php

I have defined constant in header.php file:

define( 'HOME_URL', esc_url( home_url() ) );

and used in functions.php file:

function woocommerce_header_add_to_cart_fragment( $fragments ) {
    ob_start(); ?

    div class=cart-customlocation
        img class=cart-img align-top src=?php echo HOME_URL . '/wp-content/uploads/icons/header/cart.png'; ? 
        div id=cart-count class=d-inline-block?php echo WC()-cart-cart_contents_count; ?/div
        div class=cart-description d-inline-block ml-4
            div id=cart-titleCart/div
            div id=cart-total?php echo WC()-cart-get_cart_total(); ?/div
        /div
    /div

    ?php
    $fragments['div.cart-customlocation'] = ob_get_clean();
    return $fragments;

    ob_start();
    ?

    div class=mini-cart
        
        ?php woocommerce_mini_cart(); ?
        
    /div

    ?php
    $fragments['div.mini-cart'] = ob_get_clean();
    return $fragments;
}
add_filter( 'woocommerce_add_to_cart_fragments', 'woocommerce_header_add_to_cart_fragment' );

and getting notice: bWarning/b: Use of undefined constant HOME_URL - assumed 'HOME_URL'...