TPS1HC100-Q1
ZHCSLK6A –JULY 2021 –REVISED DECEMBER 2021
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9.2.1 Design Requirements
Component
Description
Purpose
TVS
SMBJ39CA (optional)
220 nF (optional)
100 nF
Filter voltage transients coming from battery (ISO7637-2)
Better EMI performance
CVBB
CIC
Minimal amount of capacitance on input for EMI mitigation
There to hold the rail for the LDO; however, helps to filter voltage
transients on supply rail. Not a requirement.
CBULK
10 uF (optional)
RPROT
RILIM
Protection resistor for microcontroller and device I/O pins
Set current limit threshold
5 kΩ
7 kΩ–70 kΩ
1kΩ
RSNS
Translate the sense current into sense voltage.
Coupled with RPROT on the SNS line creates a low pass filter to filter out
noise going into the ADC of the MCU
CFILTER
100 nF
CVOUT
RGND
DGND
22 nF
Improves EMI performance, filtering of voltage transients
Stabilize GND potential during turn-off of inductive load
Keeps GND close to system ground during normal operation
1 kΩ
BAS21 Diode
9.2.2 Detailed Design Procedure
To keep maximum voltage on the SNS pin at an acceptable range for the system, calculate the RSNS as in 方程
式1. To achieve better current sense accuracy. A 1% accuracy or better resistor is preferred.
(VSNSFH –VHR) × KSNS / ILOAD,max ≤RSNS ≤VADC,min × KSNS / ILOAD,min
(12)
表9-1. Typical Application
Parameter
Value
5 V
VDIAG_EN
ILOAD,max
ILOAD,min
VADC,min
VHR
2 A
5 mA
5 mV
1 V
For this application, an RSNS value of approximately 1 kΩcan be chosen to satisfy the equation requirements.
(5 V –1 V) × 1040 / 4 A ≤≈1 kΩ≤5 mV × 1040 / 5 mA
(13)
In other applications, more emphasis can be put on the lower end measurable values, which can increase
RSNS. Likewise if the higher currents are of more interest the RSNS can be decreased. Note that the maximum
current that can be measured without saturation is 6 A.
Having the maximum SNS voltage scale with the DIAG_EN voltage removes the need for a Zener diode on the
SNS pin going to the ADC.
The current limit must be set to an acceptable level, so with the KCL tolerances, the current limit of 4A is chosen.
To set the programmable current limit value at 4 A , calculate the RLIM as in Equation 12.
RLIM = KCL / ILIM = 45 / 4 = 11.25 kΩ
(14)
For a more accurate current limit estimation with the error tolerances of KCL see the Current Limit Accuracy
section and use the graph to estimate the error at each desired current limit value.
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