diff --git a/examples/device/cdc_msc_hid/src/main.c b/examples/device/cdc_msc_hid/src/main.c
index 1fa0fead1..a8ef0575c 100644
--- a/examples/device/cdc_msc_hid/src/main.c
+++ b/examples/device/cdc_msc_hid/src/main.c
@@ -210,13 +210,15 @@ void tud_umount_cb(void)
   blink_interval_ms = 250;
 }
 
-// Invoked when device is suspended
+// Invoked when usb bus is suspended
+// USB specs: device can only draw up to 2.5 mA from bus
 void tud_suspend_cb(bool remote_wakeup_en)
 {
   (void) remote_wakeup_en;
   blink_interval_ms = 2500;
 }
 
+// Invoked when usb bus is resumed
 void tud_resume_cb(void)
 {
   blink_interval_ms = 1000;
diff --git a/src/device/usbd.h b/src/device/usbd.h
index 27bfe305b..2365d645e 100644
--- a/src/device/usbd.h
+++ b/src/device/usbd.h
@@ -76,16 +76,16 @@ bool tud_remote_wakeup(void);
 // Application Callbacks (WEAK is optional)
 //--------------------------------------------------------------------+
 
-// Callback invoked when device is mounted (configured)
+// Invoked when device is mounted (configured)
 ATTR_WEAK void tud_mount_cb(void);
 
-// Callback invoked when device is unmounted
+// Invoked when device is unmounted
 ATTR_WEAK void tud_umount_cb(void);
 
-// Callback invoked when device is suspended
+// Invoked when usb bus is suspended, max bus current draw is 2.5 mA
 ATTR_WEAK void tud_suspend_cb(bool remote_wakeup_en);
 
-// Callback invoked when device is resumed
+// Invoked when usb bus is resumed
 ATTR_WEAK void tud_resume_cb(void);
 
 #ifdef __cplusplus