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SC7755
ELECTRICITY POWER METER CIRCUIT
DESCRIPTION
The SC7755 is a high accuracy electrical energy measurement IC that can provides superior stability and accuracy over extremes in environmental conditions and over time. The SC7755 does not exhibit any creep when there is no load. The SC7755 supplies average real power information on the low frequency outputs F1 and F2. This logic outputs may be used to directly drive an electromechanically counter or interface to an MCU. The CF logic output gives instantaneous real power information. This output is intended to be used for calibration purposes, or interfacing to an MCU. The SC7755 includes a power supply monitoring circuit on the AVDD supply pin. If the supply falls below 4V, the SC7755 will be the same time. The SC7755 provides synchronous frequency output for autoreading meter system. The CF logic output is synchronous with the F1 and F2 logic output to ensure the show value of the meter is consonant with the real value. reset and F1, F2 will be set to logic high, CF will be set to logic low at ORDERING INFORMATION Device SC7755S SC7755 Package SSOP-24-300-0.65 SDIP-24-300-2.54
SDIP-24 SSOP-24
FEATURES
* Single 5V supply, low power. * On-chip power supply monitoring. * On-chip reference with external overdrive capability. * Supplies average real power on the frequency outputs F1 and F2, which can drive for electromechanical counters directly. * The high frequency output CF is intended for calibration and supplies instantaneous real power. * Less than 0.1% error over a dynamic range of 500 to 1. * On-chip creep protection (No load threshold). * The logic output REVP can be used to indicate a potential miswiring or negative power. * A PGA in the current channel make flexible to select the shunt and burden resistance.
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SC7755
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATING (Tamb=25C, unless otherwise specified)
Characteristics AVDD to AGND DVDD to DGND Analog Input Voltage to AGND V1P, V1N, V2P and V2N Reference Input voltage to AGND Digital Input Voltage to DGND Digital Output Voltage to DGND Power Dissipation Operating Temperature Range Industrial (A, B version) Storage Temperature Junction Temperature Symbol AVDD DVDD AVIN VREF DVIN DVOUT PD TOPR TSTG TJ Value -0.3 ~ +7 -0.3 ~ +7 -6 ~ +6 -0.3 ~ AVDD+0.3 -0.3 ~ DVDD+0.3 -0.3 ~ DVDD+0.3 450 -40~ +85 -65~ +150 +150 Unit V V V V V V mW C C C
ELECTRICAL CHARACTERISTICS (Tamb=25C, unless otherwise specified)
Characteristics Power Supply Analog Power Supply Digital Power Supply Analog Input Current Digital Input Current AVDD DVDD AIDD DIDD 5V5% 5V5% (2mA) TYP. (1.5mA) TYP. 4.75 4.75 ------5.25 5.25 3 2.5 V Symbol Test conditions Min. Typ. Max. Unit
mA
(To be continued)
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SC7755
(Continued) Characteristics ACCURACY Measurement Error
1
Symbol
Test conditions
Min.
Typ.
Max.
Unit
Gain=1 Gain=2 Gain=8 Gain=16 EM
Over a dynamic range 500 to 1 Over a dynamic range 500 to 1 Over a dynamic range 500 to 1 Over a dynamic range 500 to 1 EP AC/ DC =0 and AC/ DC =1
-------
0.1 0.1 0.1 0.1 --0.01 0.01
----0.1 0.1 --0.014% *Fbase
% % % % % % Hz
on
Channel 1 Phase Error Between Channels
1
V1 Phase Lead 37 V1 Phase Lag 60 CFA CFD Fmin V1=100mV, V2=100mV, AC/ DC =1 S0=S1=1 G0=G1=0 V1=100mV, V2=100mV,
Output Frequency Rejection (AC) Output Frequency Rejection (DC) The MIN. Frequency of Output (F1, F2) ANALOG INPUTS Maximum Signal Levels Input Impedance (DC) Bandwidth (-3dB) ADC Offset Error Gain Error
1 1 1,2
---
VDD=DVDD=5V250mV --
LEVS IMIN BW EADC EG EGM
V1P, VIN V2N and V2P to AGND CLKIN=3.58MHz CLKIN/256, CLKIN=3.58MHz
-400 ---
--14 -4 0.2
1 --15 ---
V k kHz mV % %
V1=470mV, V2=660mV External 2.5V reference
---
Gain Error Match
REFERENCE INPUT REFIN/OUT Input Voltage Range Input Impedance Input Capacitance ON-CHIP REFERENCE Reference Error Temperature Coefficient CLKIN Input Clock Frequency LOGIC INPUTS3 Input High Voltage Input Low Voltage Input Current Input Capacitance VINH VINL IIN CIN DVDD=5V5% DVDD=5V5% Typically DVDD 10nA, VIN=0V to 2.4 --------0.8 3 10 V V A pF CLKIN Note all specifications for CLKIN of 3.58MHz 1 -4 MHz ER TC Nominal 2.5V ---30 200 60 mV ppm/C VINR IMIN CIN 2.5V8% --2.3 3.7 ----2.7 -10 V k pF
(To be continued)
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SC7755
(Continued) Characteristics LOGIC OUTPUTS3 Output F1 and F2 Voltage Output Voltage Output CF and REVP Voltage Output Voltage Low High Low High VOH VOL VOH VOL ISOURCE=10mA DVDD=5V ISINK=10mA DVDD=5V ISOURCE=5mA DVDD=5V ISINK=5mA DVDD=5V 4.5 -4 ------0.5 -0.5 V V V V Symbol Test conditions Min. Typ. Max. Unit
PIN CONFIGURATIONS
PIN DESCRIPTION
Pin No. 1 2 3 4 5 6 7 8 9 10 Symbol DVDD AC/ DC AVDD NC V1P V1N V2N V2P
RESET
Description Digital Power Supply. High Pass Filter Select. The pin should be high in power metering applications. Analog Power Supply. No connect. Positive and Negative Inputs for Channel 1 (Current Channel). Channel 1 has a PGA and the gain selections are outlined in Table I. The maximum signal level at these pins is 1V with respect to AGND. Negative and Positive Inputs for Channel 2 (Voltage Channel). The maximum differential input voltage is 660mV for specified operation. The maximum signal level at these pins is 1V with respect to AGND. Reset Pin for the SC7755. A logic low is valid; Reference voltage input/output pin. (To be continued)
REFIN/OUT
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SC7755
(Continued) Pin No. 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Symbol AGND SCF S1 S0 G1 G0 CLKIN CLKOUT NC REVP DGND CF F2 F1 Analog ground. Select Calibration Frequency. This logic input is used to select the frequency on the calibration output CF. Table III shows how the calibration frequencies are selected. Select one of four possible frequencies for the digital-to-frequency conversion. See Table II and Table III Select gains for Channel 1, See Table I 3.58MHZ crystal oscillator input pin 3.58MHZ crystal oscillator output pin No connect. State indication pin. While negative power or a potential miswriting occurs, it will be set to logic high. Digital ground. Calibration Frequency Logic Output.. Low Frequency Logic Outputs. They can be used to directly drive a stepper motor or electromechanical impulse counter Description
TIMIING CHARACTERISTICS1,2
(AVDD=DVDD=5V5%, AGND=DGND=0V, On-chip Reference, CLKIN=3.58MHZ, TMIN to TMAX=-40C~+85C.) Parameter t1
3
Test Condition F1 and F2 Pulse-width F1 and F2 Pulse Period. Time Between F1 Falling Edge and F2 Falling Edge CF Pulse-width CF Pulse Period. Minimum Time Between F1 and F2 Pulse
Test Data 275 See Table II 1/2 t2 90 See Table III CLKIN/4
Units ms sec sec ms sec sec
t2 t3 t4
3,4
t5 t6
NOTE: 1. Sample tested during initial release and after any redesign or process change that may after this parameter. 2. See the following figure. 3. The pulse-widths of F1, F2 and CF are not fixed for higher output frequencies. t1
F1 t6 t2 F2 t3 t4 CF t5
Timing Diagram for Frequency outputs
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SC7755
Timing Diagram for Frequency Outputs shows a timing diagram for the various frequency outputs of the SC7755. The low frequency outputs, F1 and F2 can drive electromechanical counters and two phase stepper motors directly. As the figure show, the F1 and F2 outputs provide two alternating low going pulses. The pulse width (t1) is set at 275ms and the time between the falling edges of F1 and F2 (t3) is approximately half the period of F1 (t2). If however the period of F1 and F2 falls below 550 ms (1.81Hz) the pulse width of F1 and F2 is set to half of their period. The frequency of F1 and F2 corresponds to the input voltages, and F=
2 8.06*V1*V2*G*Fbase/ VREF The values of G and Fbase can be set by consumers, and the selection of G
and Fbase please refer to the table I and table III , V1 and V2 are the rms value of the two inputs, VREF is the voltage of reference, whose value is 2.5+0.2v when the internal bandgap reference of SC7755 is valid. The maximum output frequencies for F1 and F2 are shown in Table II. The high frequency output, CF is intended for calibration and supplies instantaneous real power. CF produces a 90ms wide active high pulse (t4) at a frequency proportional to active power. The CF output frequencies are given in Table III. As in the case of F1 and F2, if the period of CF (t5) falls below 180ms, the CF pulse-width is set to half the period.
APPENDIX
Table I. gain selection for channel 1 G1 0 0 1 1 G0 0 1 0 1 G 1 2 8 16 Maximum Differential Signal 470mV 235mV 60mV 30mV
Table II. Maximum output frequency on F1 and F2 S1 0 0 1 1 S2 0 1 0 1 Max Frequency for DC Inputs (Hz) 0.68 1.36 2.72 5.44 Max Frequency for AC Inputs (Hz) 0.34 0.68 1.36 2.72
Table III. Maximum output frequency on CF SCF 1 0 1 0 1 0 1 0 S1 0 0 0 0 1 1 1 1 alter. S0 0 0 1 1 0 0 1 1 Fbase(Hz) 1.7 1.7 3.4 3.4 6.8 6.8 13.6 13.6 XTAL/CLKIN* 3.579MHz/2 3.579MHz/2 3.579MHz/2 3.579MHz/2
21 21
CF Max for AC signals (Hz) 128xF1, F2 64xF1, F2 64xF1, F2 32xF1, F2 32xF1, F2 16xF1, F2 16xF1, F2 2048xF1, F2
20 20
3.579MHz/219 3.579MHz/2 3.579MHz/2 3.579MHz/2
19 18 18
NOTE: *Fbase is a binary fraction of the master clock and therefore will vary if the specified CLKIN frequency is
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SC7755
TYPICAL APPLICATION CIRCUIT
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SC7755
PACKAGE OUTLINE
SSOP-24-300-0.65 UNIT: mm
12(2x)
7.80.2
5.250.2 0.1520.05
0.3
0.65
8.150.2 12(4x) 1.750.05
SDIP-24-300-2.54
0.150.05
UNIT: mm
2.54 0.250.05 15 degree
6.400.25
1.27
29.720.3
0.5 MIN
0.46 0.89MAX
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3.00MIN
4.36MAX
7.62
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SC7755
HANDLING MOS DEVICES:
Electrostatic charges can exist in many things. All of our MOS devices are internally protected against electrostatic discharge but they can be damaged if the following precautions are not taken: * Persons at a work bench should be earthed via a wrist strap. * Equipment cases should be earthed. * All tools used during assembly, including soldering tools and solder baths, must be earthed. * MOS devices should be packed for dispatch in antistatic/conductive containers.
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