UCD3138: Questions of PMBus

Part Number:UCD3138

Hi TI experts,

I  used UCD3138OL64EVM to test PMBus write command with 100khz trans speed to  microchip pickit serial analyzer,but I found ACK's clock is not matched that I set 100khz,

please see the waveform as below , 

ex: Write data [B6h][48h][D0h][39h][4Dh][2Eh][53h][41h][30h][35h] , that i measured ACK clock is not 100khz? thanks.