function proximoCampo(atual,proximo){
 var campo = atual.value.split('_').join('');
  if(campo.length >= atual.maxLength){
      alert("Campo = "+proximo);
      document.getElementById(proximo).focus();
  }
}

<p:outputLabel value="Cep:" for="inputText-cep" />
                <p:inputMask id="inputText-cep" mask="99999-999"  size="9" maxlength="9" onkeyup="proximoCampo(this, 'inputText-endereco')"
                    onmouseover="meuMouseOver()"
                    onmouseout="meuMouseOut()"
                    value="#{cadastroFuncionarioBean.logradouroModel.cep}">
                    <p:ajax event="blur"
                        listener="#{cadastroFuncionarioBean.encontraEndereco}"
                        process="inputText-cep" update="inputText-endereco" />
                </p:inputMask>