TTL not working properly when worked on upsert function in mongodb using mongoose

Hi i came across one concept called as ttl in mongodb and tried the same in a insert operation using mongoose.Below is the code

mongoose = require('mongoose');
var Schema = mongoose.Schema;
var META_CTS_DB = mongoose.createConnection('mongodb://localhost/META');
var ttl= require('mongoose-ttl');
var date1=new Date();
var ServiceSchema = new Schema({
_id:String, 
CURDATE:{type:Date,index:true},
SERVICE_PROTOCOL:String, 
});
ServiceSchema.plugin(ttl, { ttl:5000 });
var MasterDBdata = META.model('ServiceSchema',ServiceSchema,'API_KEY_91994094177912_SERVICE_ID_0008_SERVICE_CONFIG');
var item = new MasterDBdata({'_id':'SERVICE_ID_0006','CURDATE':date1,'SERVICE_PROTOCOL':'Nil'});
item.save();

The ttl worked fine for this and the collection did get deleted.But when i performed the same for a update function as below

MasterDBdata.update({'_id':'SERVICE_ID_0006'},{'CURDATE':date1,'SERVICE_PROTOCOL':'hhl'},{upsert:true},function (err){

                                                        if (err) return handleError(err);
                                                        console.log('\n data stored in Database...')});

The ttl function didnt seem to work properly.Any idea regarding the behaviour of ttl and its performance on these functions will be really helpful.Thanks in advance