diff --git a/doc/doxygen/lwip.Doxyfile b/doc/doxygen/lwip.Doxyfile
index 9855c053..c8aaaabb 100644
--- a/doc/doxygen/lwip.Doxyfile
+++ b/doc/doxygen/lwip.Doxyfile
@@ -2082,6 +2082,7 @@ PREDEFINED             = __DOXYGEN__=1 \
                          LWIP_IGMP=1 \
                          LWIP_TCP=1 \
                          LWIP_ALTCP=1 \
+                         LWIP_ALTCP_TLS=1 \
                          LWIP_IPV6_SCOPES=1 \
                          TCP_LISTEN_BACKLOG=1 \
                          LWIP_SNMP=1 \
@@ -2118,7 +2119,8 @@ PREDEFINED             = __DOXYGEN__=1 \
                          SO_REUSE=1 \
                          SO_REUSE_RXTOALL=1 \
                          LWIP_HAVE_SLIPIF=1 \
-                         LWIP_6LOWPAN=1
+                         LWIP_6LOWPAN=1 \
+                         HTTPD_ENABLE_HTTPS=1
  
 # If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
 # tag can be used to specify a list of macro names that should be expanded. The
diff --git a/src/apps/httpd/httpd.c b/src/apps/httpd/httpd.c
index 5c219338..53146738 100644
--- a/src/apps/httpd/httpd.c
+++ b/src/apps/httpd/httpd.c
@@ -2593,6 +2593,11 @@ httpd_init(void)
 }
 
 #if HTTPD_ENABLE_HTTPS
+/**
+ * @ingroup httpd
+ * Initialize the httpd: set up a listening PCB and bind it to the defined port.
+ * Also set up TLS connection handling (HTTPS).
+ */
 void
 httpd_inits(struct altcp_tls_config *conf)
 {
diff --git a/src/apps/smtp/smtp.c b/src/apps/smtp/smtp.c
index 44c4b263..86163459 100644
--- a/src/apps/smtp/smtp.c
+++ b/src/apps/smtp/smtp.c
@@ -367,6 +367,11 @@ smtp_set_server_port(u16_t port)
 }
 
 #if LWIP_ALTCP && LWIP_ALTCP_TLS
+/** @ingroup smtp
+ * Set TLS configuration for next SMTP connection
+ *
+ * @param tls_config TLS configuration
+ */
 void
 smtp_set_tls_config(struct altcp_tls_config *tls_config)
 {
diff --git a/src/include/lwip/altcp_tls.h b/src/include/lwip/altcp_tls.h
index aff57128..e542959c 100644
--- a/src/include/lwip/altcp_tls.h
+++ b/src/include/lwip/altcp_tls.h
@@ -2,6 +2,8 @@
  * @file
  * Application layered TCP/TLS connection API (to be used from TCPIP thread)
  *
+ * @defgroup altcp_tls TLS layer
+ * @ingroup altcp
  * This file contains function prototypes for a TLS layer.
  */
 
@@ -51,13 +53,26 @@
 extern "C" {
 #endif
 
+/** @ingroup altcp_tls
+ * ALTCP_TLS configuration handle, content depends on port (e.g. mbedtls) 
+ */
 struct altcp_tls_config;
 
+/** @ingroup altcp_tls
+ * Create an ALTCP_TLS server configuration handle
+ */
 struct altcp_tls_config *altcp_tls_create_config_server_privkey_cert(const u8_t *privkey, size_t privkey_len,
                             const u8_t *privkey_pass, size_t privkey_pass_len,
                             const u8_t *cert, size_t cert_len);
+
+/** @ingroup altcp_tls
+ * Create an ALTCP_TLS client configuration handle
+ */
 struct altcp_tls_config *altcp_tls_create_config_client(const u8_t *cert, size_t cert_len);
 
+/** @ingroup altcp_tls
+ * Create new ALTCP_TLS layer
+ */
 struct altcp_pcb *altcp_tls_new(struct altcp_tls_config* config, struct altcp_pcb *inner_pcb);
 
 #ifdef __cplusplus
diff --git a/src/include/lwip/apps/mqtt.h b/src/include/lwip/apps/mqtt.h
index 3c2fd82f..8f3af4aa 100644
--- a/src/include/lwip/apps/mqtt.h
+++ b/src/include/lwip/apps/mqtt.h
@@ -79,6 +79,7 @@ struct mqtt_connect_client_info_t {
   u8_t will_qos;
   u8_t will_retain;
 #if LWIP_ALTCP && LWIP_ALTCP_TLS
+  /** TLS configuration for secure connections */
   struct altcp_tls_config *tls_config;
 #endif
 };