Other Parts Discussed in Thread: BQ24075, LP87702
I am using the LP87702-Q1 as the primary supply in my design. There is also a BQ24075 for battery management and the output of the BQ is input to the LP. With only battery plugged in, The LP87702 boots fine with default OTP settings (1.8V out on Buck0) and I can configure the LP87702 fine and set the output of both bucks to 3.3V. But as soon as I plug in USB (with battery still connected) or power it only on USB, I can see that the LP87702 resets and Buck0 outputs 1.95V (actually i measured the output and its weirdly 1.95V instead of 1.8V. I get the expected 1.8V on default boot when using only battery). If I then try to set BUCK0_VOUT to 0xFF, the output only goes up to 2.25V only (I read back BUCK0_VOUT to confirm it was infact 0xFF). Also, BUCK1 does not output anything. I am not sure why this is happening. VIN_B0, VIN_B1 and VANA are tied together and are at 4.85V when I plug in USB.
This is the default register state when USB power is supplied
[0] unsigned char 0x00 '\x00' (Hex) 0x2000FFC4 [1] unsigned char 0xB6 '\xb6' (Hex) 0x2000FFC5 [2] unsigned char 0x1B '\x1b' (Hex) 0x2000FFC6 [3] unsigned char 0x2C ',' (Hex) 0x2000FFC7 [4] unsigned char 0x1B '\x1b' (Hex) 0x2000FFC8 [5] unsigned char 0x34 '4' (Hex) 0x2000FFC9 [6] unsigned char 0xB1 '\xb1' (Hex) 0x2000FFCA [7] unsigned char 0x7D '}' (Hex) 0x2000FFCB [8] unsigned char 0x5B '[' (Hex) 0x2000FFCC [9] unsigned char 0x32 '2' (Hex) 0x2000FFCD [10] unsigned char 0x23 '#' (Hex) 0x2000FFCE [11] unsigned char 0x14 '\x14' (Hex) 0x2000FFCF [12] unsigned char 0x05 '\x05' (Hex) 0x2000FFD0 [13] unsigned char 0x00 '\x00' (Hex) 0x2000FFD1 [14] unsigned char 0x00 '\x00' (Hex) 0x2000FFD2 [15] unsigned char 0x8B '\x8b' (Hex) 0x2000FFD3 [16] unsigned char 0x08 '\x08' (Hex) 0x2000FFD4 [17] unsigned char 0xC4 '\xc4' (Hex) 0x2000FFD5 [18] unsigned char 0x41 'A' (Hex) 0x2000FFD6 [19] unsigned char 0x3F '?' (Hex) 0x2000FFD7 [20] unsigned char 0x18 '\x18' (Hex) 0x2000FFD8 [21] unsigned char 0x9E '\x9e' (Hex) 0x2000FFD9 [22] unsigned char 0x9F '\x9f' (Hex) 0x2000FFDA [23] unsigned char 0x8A '\x8a' (Hex) 0x2000FFDB [24] unsigned char 0xA3 '\xa3' (Hex) 0x2000FFDC [25] unsigned char 0x03 '\x03' (Hex) 0x2000FFDD [26] unsigned char 0xBF '\xbf' (Hex) 0x2000FFDE [27] unsigned char 0x1F '\x1f' (Hex) 0x2000FFDF [28] unsigned char 0xDC '\xdc' (Hex) 0x2000FFE0 [29] unsigned char 0x0F '\x0f' (Hex) 0x2000FFE1 [30] unsigned char 0x00 '\x00' (Hex) 0x2000FFE2 [31] unsigned char 0x00 '\x00' (Hex) 0x2000FFE3 [32] unsigned char 0x01 '\x01' (Hex) 0x2000FFE4 [33] unsigned char 0x00 '\x00' (Hex) 0x2000FFE5 [34] unsigned char 0x00 '\x00' (Hex) 0x2000FFE6 [35] unsigned char 0x00 '\x00' (Hex) 0x2000FFE7 [36] unsigned char 0x00 '\x00' (Hex) 0x2000FFE8 [37] unsigned char 0x09 '\x09' (Hex) 0x2000FFE9 [38] unsigned char 0x00 '\x00' (Hex) 0x2000FFEA [39] unsigned char 0x00 '\x00' (Hex) 0x2000FFEB [40] unsigned char 0x01 '\x01' (Hex) 0x2000FFEC [41] unsigned char 0x88 '\x88' (Hex) 0x2000FFED [42] unsigned char 0x01 '\x01' (Hex) 0x2000FFEE [43] unsigned char 0xDD '\xdd' (Hex) 0x2000FFEF [44] unsigned char 0x0D '\x0d' (Hex) 0x2000FFF0 [45] unsigned char 0x3F '?' (Hex) 0x2000FFF1 [46] unsigned char 0x00 '\x00' (Hex) 0x2000FFF2 [47] unsigned char 0x00 '\x00' (Hex) 0x2000FFF3 [48] unsigned char 0x00 '\x00' (Hex) 0x2000FFF4 [49] unsigned char 0x06 '\x06' (Hex) 0x2000FFF5 [50] unsigned char 0x01 '\x01' (Hex) 0x2000FFF6 [51] unsigned char 0x00 '\x00' (Hex) 0x2000FFF7 [52] unsigned char 0x00 '\x00' (Hex) 0x2000FFF8 [53] unsigned char 0x03 '\x03' (Hex) 0x2000FFF9
Register Settings after I write (which sets BUCK0_VOUT to 2.25V)
[0] unsigned char 0x00 '\x00' (Hex) 0x2000FFC4 [1] unsigned char 0xB6 '\xb6' (Hex) 0x2000FFC5 [2] unsigned char 0x19 '\x19' (Hex) 0x2000FFC6 [3] unsigned char 0x04 '\x04' (Hex) 0x2000FFC7 [4] unsigned char 0x19 '\x19' (Hex) 0x2000FFC8 [5] unsigned char 0x04 '\x04' (Hex) 0x2000FFC9 [6] unsigned char 0xFF '\xff' (Hex) 0x2000FFCA [7] unsigned char 0xFF '\xff' (Hex) 0x2000FFCB [8] unsigned char 0x58 'X' (Hex) 0x2000FFCC [9] unsigned char 0x32 '2' (Hex) 0x2000FFCD [10] unsigned char 0x23 '#' (Hex) 0x2000FFCE [11] unsigned char 0x14 '\x14' (Hex) 0x2000FFCF [12] unsigned char 0x05 '\x05' (Hex) 0x2000FFD0 [13] unsigned char 0x00 '\x00' (Hex) 0x2000FFD1 [14] unsigned char 0x00 '\x00' (Hex) 0x2000FFD2 [15] unsigned char 0x8B '\x8b' (Hex) 0x2000FFD3 [16] unsigned char 0x08 '\x08' (Hex) 0x2000FFD4 [17] unsigned char 0xC4 '\xc4' (Hex) 0x2000FFD5 [18] unsigned char 0x41 'A' (Hex) 0x2000FFD6 [19] unsigned char 0x3F '?' (Hex) 0x2000FFD7 [20] unsigned char 0x18 '\x18' (Hex) 0x2000FFD8 [21] unsigned char 0xBE '\xbe' (Hex) 0x2000FFD9 [22] unsigned char 0x9F '\x9f' (Hex) 0x2000FFDA [23] unsigned char 0x8A '\x8a' (Hex) 0x2000FFDB [24] unsigned char 0xA3 '\xa3' (Hex) 0x2000FFDC [25] unsigned char 0x00 '\x00' (Hex) 0x2000FFDD [26] unsigned char 0xBF '\xbf' (Hex) 0x2000FFDE [27] unsigned char 0x18 '\x18' (Hex) 0x2000FFDF [28] unsigned char 0xDC '\xdc' (Hex) 0x2000FFE0 [29] unsigned char 0x0F '\x0f' (Hex) 0x2000FFE1 [30] unsigned char 0x00 '\x00' (Hex) 0x2000FFE2 [31] unsigned char 0x00 '\x00' (Hex) 0x2000FFE3 [32] unsigned char 0x01 '\x01' (Hex) 0x2000FFE4 [33] unsigned char 0x00 '\x00' (Hex) 0x2000FFE5 [34] unsigned char 0x00 '\x00' (Hex) 0x2000FFE6 [35] unsigned char 0x00 '\x00' (Hex) 0x2000FFE7 [36] unsigned char 0x00 '\x00' (Hex) 0x2000FFE8 [37] unsigned char 0x09 '\x09' (Hex) 0x2000FFE9 [38] unsigned char 0x00 '\x00' (Hex) 0x2000FFEA [39] unsigned char 0x00 '\x00' (Hex) 0x2000FFEB [40] unsigned char 0x01 '\x01' (Hex) 0x2000FFEC [41] unsigned char 0x88 '\x88' (Hex) 0x2000FFED [42] unsigned char 0x01 '\x01' (Hex) 0x2000FFEE [43] unsigned char 0xDD '\xdd' (Hex) 0x2000FFEF [44] unsigned char 0x0D '\x0d' (Hex) 0x2000FFF0 [45] unsigned char 0x3F '?' (Hex) 0x2000FFF1 [46] unsigned char 0x00 '\x00' (Hex) 0x2000FFF2 [47] unsigned char 0x00 '\x00' (Hex) 0x2000FFF3 [48] unsigned char 0x00 '\x00' (Hex) 0x2000FFF4 [49] unsigned char 0x06 '\x06' (Hex) 0x2000FFF5 [50] unsigned char 0x01 '\x01' (Hex) 0x2000FFF6 [51] unsigned char 0x00 '\x00' (Hex) 0x2000FFF7 [52] unsigned char 0x00 '\x00' (Hex) 0x2000FFF8 [53] unsigned char 0x03 '\x03' (Hex) 0x2000FFF9
What am I missing?
