ZSPM1025A
True Digital PWM Controller (Single-Phase, Single-Rail)
3.3.6.
Current Sensing
The ZSPM1025A offers cycle-by-cycle average current sensing with configurable over-current protection. A
dedicated ADC is used to provide fast and accurate current information over the switching period. The acquired
information is compared with configurable current thresholds to report warning and error levels to the user. DCR
current sensing across the inductor and dedicated shunt resistors are supported. Additionally, the device uses
DCR temperature compensation via the external temperature-sensing element. This increases the accuracy of
the current sense method by counteracting the significant change of the DCR over temperature.
To acquire accurate current information, the selection of the current sensing circuit is of critical importance. The
schematic of the required current sensing circuitry is shown in Figure 3.4 for the widely used DCR current-sensing
method, which uses the parasitic resistance of the inductor to acquire the current information. The principle is
based on a matched time-constant between the inductor and the low-pass filter built from a 2.15kΩ resistor
mounted on the Murata Power Block and C8. Resistor R6 should be a precision 2.15kΩ resistor in order to
provide good DC voltage rejection, .i.e. reduce the influence of the output voltage level in the current measure-
ment.
Figure 3.4
Inductor Current Sensing Using the DCR Method
Murata
OKLP-X/25-W12-C
L
DCR
+Vout
2.15 kOhm
+CS
-CS
C8
220nF
ZSPM1025
R6
2.15 kOhm
ISNSP
ISNSN
End-of-line calibration is supported so that the ZSPM1025A can achieve improved accuracy over the full output
current range. The full calibration method is detailed in the ZSPM10xx Application Note—Programming and
Calibration. This allows the user to correct mismatches between the nominal DCR value used to configure the
device and the actual DCR value in the application caused by effects such as manufacturing variations. The
calibration range is limited to +/- 50% of the nominal DCR value.
© 2013 Zentrum Mikroelektronik Dresden AG — Rev. 1.00
All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the
prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice.
Data Sheet
October 24, 2013
19 of 46
ETC [ ETC ]
