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HV7801 High Side Current Monitor
8V to 450V, Gain of 5
Features
Supply voltage 8V to 450V Voltage output device Typical gain 51% Max VSENSE 500mV Fast rise and fall times, 700ns to 2s Maximum quiescent current 50A
General Description
The HV7801 high side current monitor IC transfers a highside current measurement voltage to its ground referenced output with an accurate voltage gain of five. The measurement voltage typically originates at a current sense resistor which is located in a "high side" circuit, such as the positive supply line. This monitor IC features a very wide input voltage range, high accuracy of transfer ratio, small size, low component count, low power consumption, ease of use, and low cost. Offline applications, battery, and portable applications can be served well due to the wide input voltage range and the low quiescent current.
Applications
SMPS current monitor Battery current monitor Motor control
Typical Application Circuit
VSENSE 8V to 450V Input ISENSE
IN VO U T = 5 * VS E N S E
LOAD
HV7801
GND OUT
VOUT V
HV7801
Ordering Information
Device HV7801
-G indicates package is RoHS compliant (`Green')
Thermal Resistance
Package Option 5-Lead SOT-23 HV7801K1-G Package 5-Lead SOT-23
Note: Thermal testboard per JEDEC JESD51-7
ja 191 OC/W
Pin Configuration
OUT 5 GND 4
Absolute Maximum Ratings
Parameter VIN, VLOAD VOUT VSENSE ILOAD Operating ambient temperature Operating junction temperature Storage temperature Value -0.5V to +450V -0.5V to +10V -0.5V to +5.0V 10mA 0C to +70C -40C to +125C -65C to +150C
1 2 3 IN LOAD NC
5-Lead SOT-23
(top view)
Product Marking
7BYW
Y = Last Digit of Year Sealed W = Code for Week Sealed = "Green" Packaging
Absolute maximum ratings are those values beyond which damage to the device may occur. Functional operation under these conditions is not implied. Continuous operation of the device at the absolute rating level may affect device reliability. All voltages are referenced to device ground.
5-Lead SOT-23
Electrical Characteristics (T = 25C unless otherwise specified, V
A
IN
= 8.0V to 450V)
Symbol
Parameter
Min
Typ
Max
Units
Conditions
Supply
VIN IQ ROUT Supply voltage* Quiescent supply current 8.0 450 50 V A --VIN = 8V to 450V, VSENSE = 0mV --VSENSE = 0mV mV VSENSE = 100mV VSENSE = 200mV VSENSE = 500mV VSENSE step 5mV to 500mV VSENSE step 0mV to 500mV VSENSE step 500mV to 0mV
Input and Output
OUT pin output resistance 0 VOUT Output voltage 445 940 2425 16.5 50 555 1060 2575 k
Dynamic Characteristics
tRISE tFALL Output rise time, 10% to 90% Output fall time, 90% to 10% 0.7 0.7 2.0 2.0 s s
*Values apply over the full temperature range.
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HV7801
Block Diagram
VSENSE ISENSE
Typical use is measurement of line or load current for purpose of overcurrent protection, metering and current regulation. High side current sensing, as opposed to ground referenced or low side current sensing, is desirable or required when:
R SENSE RP (Optional, see text)
IN
LOAD
The current to be measured does not flow in a circuit associated with ground. The measurement at ground level can lead to ambiguity due to changes in the grounding arrangement during field use. The introduction of a sense resistor in the system ground is undesirable due to issues with safety, EMI, or signal degradation due to common impedance coupling.
RA
Bias Circuits
Principle of Operation
The operational amplifier and MOSFET forces the voltage across RA to track VSENSE within the limit of the offset voltage of the opamp, i.e. VRA = VSENSE.
VOUT OUT RB
HV7801
GND
The current through RA returns to ground through RB. RA and RB are integrated, exhibiting tight matching and excellent tracking. By design, RB is five times larger than RA. Consequently, VRB is five times larger than VRA, thus resulting in a voltage gain of 5.
OUT Pin Loading Effects
Note that the OUT pin has an typical output resistance of 16.5k. Loading the output causes the voltage gain to drop and rise/fall times to increase.
Application Information
General
The HV7801 high side current monitor IC features accurate current sensing, small size, low component count, low power consumption, exceptional input voltage range, ease of use and low cost.
For example, assuming output resistance is 16.5k, the load resistance should exceed 16.5M in order to limit the drop in gain to 1 part in 1000. Again assuming output resistance is 16.5k, capacitive loading of 6pF results in a response pole with a time constant of 100ns, not high enough to materially affect the output rise and fall times (about 700ns).
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HV7801
Sense Resistor Considerations
Limit the sense resistor voltage to 500mV during normal operating conditions. Limit the power dissipation in the sense resistor to suit the application; a high sense voltage benefits accuracy, but increases power dissipation. Consider the use of Kelvin connections for applications where considerable voltage drops may occur in the PCB traces. A layout pattern which minimizes voltage across the sense lines is shown below.
+ VSENSE
Transient Protection
Add a protection resistor (RP) in series with the LOAD pin if VSENSE can exceed 5V in a positive sense or 600mV in a negative sense, whether in a steady state or in transient conditions. A large VSENSE may occur during system startup or shutdown due to the charging and discharging of bulk storage capacitors. VSENSE may be large due to fault conditions, such as a short circuit condition, or a broken or missing sense resistor. An internal 5V Zener diode with a current rating of 10mA protects the sense amplifier inputs. The block diagram shows the orientation of this diode. The Zener diode provides clamping at 5V for a positive VSENSE and at 600mV for a negative VSENSE. Under worst case conditions, limit the Zener current to 10mA. A 100k resistor limits the maximum Zener diode current to 4.5mA when VSENSE is 450V, whether positive or negative. Note that the protection resistor may affect the bandwidth. The resistor forms an RC network with the trace and pin capacitance at the LOAD pin. A capacitance of 5pF results in a time constant of 500ns. The protection resistor may cause an offset voltage due to bias current at the LOAD input. Under worst case bias current, a 100k protection resistor could cause an offset of 100V or 0.2% of full scale. Note that the bias current is nominally zero as the LOAD is a high impedance CMOS input.
-
R SENSE
IN
LOAD
Choose a low inductance type sense resistor if preservation of bandwidth is important. The use of Kelvin connections helps by excluding the inductive voltage drop across the traces leading to the sense resistor. The inductive voltage drop may be substantial when operating at high frequencies. A trace or component inductance of just 10nH contributes an impedance of 6.2m at 100kHz, which constitutes a 6% error when using a 100m sense resistor.
Pin Description
Pin # 1 2 3 4 5 Pin Name LOAD NC IN GND OUT Description Sense amplifier input. High impedance input with Zener diode protection. Add an external protection resistor in series with LOAD if VSENSE exceeds the range of -600mV to +5V. No connect. This pin must be left floating for proper operation. Sense amplifier input and supply. Supply return. Output with a nominal output resistance of 16.5k. Preservation of accuracy may require an external buffer amplifier to prevent excessive loading.
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HV7801
5-Lead SOT-23 Package Outline (K1)
2.9x1.6mm body, 1.45mm height (max), 0.95mm pitch
D e1 5 1
Note 1 (Index Area D/2 x E1/2) 1
E1
E L2
Gauge Plane
e
b L1
L
Seating Plane
Top View
A
View B
View B
A
A2
Seating Plane
A1
Side View
A
View A-A
Note 1: This chamfer feature is optional. If it is not present, then a Pin 1 identifier must be located in the index area indicated.The Pin 1 identifier may be either a mold, or an embedded metal or marked feature.
Symbol MIN Dimension (mm) NOM MAX
A 1.45
A1 0.00 0.15
A2 0.90 1.15 1.30
b 0.30 0.50
D 2.75 2.90 3.05
E 2.60 2.80 3.00
E1 1.45 1.60 1.75
e 0.95 BSC
e1 1.90 BSC
L 0.30 0.45 0.60
L1 0.60 REF
L2 0.25 BSC
0 4
O O
1 5O 10O 15O
8O
JEDEC Registration M0-178, Variation AA, Issue C, Feb. 2000. Drawings not to scale.
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to http://www.supertex.com/packaging.html.)
Doc.# DSFP-HV7801 A042307
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