Application Note
9 of 63
V 1.2
2018-12-12
5 Output PMIC Controller/ IRPS5401
User guide with DB295 and DB296 demo boards
3
LDO Operation
The LDO input is pin 22. The input voltage has a range of 1.2 V to 5.5 V. The LDO output is pin 23.
Figure 9
LDO input
3.1
Source only mode
Set REG 0x1420 bit [8] (ldo_track_config) to 0
The LDO output has a range of 0.5 V to 3.6 V. The output is fed back to pin FB_L through a resistor divider
network. The output voltage will be set to (1+R_upper/R_lower)*0.5 V. With VOUT tied directly to FB_L, VOUT
will be set to 0.5 V…the reference voltage. The output is rated at 0.5 A. The OC_FAULT_LIMIT is read only and is
set to 0.72 A. The OV_WARN and FAULT, UV_WARN and FAULT are all read only and are a percentage of the
VOUT value set in REG 0x1420 [7:0] (ldo_target_vout). The lsb is 15.625 mV. So a value of 40h (1000/15.625 = 64
dec = 40h) would represent 1 V. Set this register to accurately represent the actual VOUT set by the external
components so that the UV and O V circuits trip at the correct value.
Figure 10
Source only mode
3.2
Sink/Source (Tracking) mode
Set REG 0x1420 bit [8] (ldo_track_config) to 1
In Tracking mode, VO_LDO must be connected directly to FB_L. An internal divider to VIN_LDO sets the
reference. The target VOUT is always ½*VIN_LDO so register ldo_target_vout has no function in tracking
mode. PMBus commands POWER_GOOD_ON and OFF also have no function in tracking mode. They are a
percentage of ½*VIN_LDO.
