ES7 CYRUSTEK | Alldatasheet
Document overview
- Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
- PDF pages: 10
Technical content
Features
Description • True RMS-to-DC Conversion
- Input level is specified up to 400mVRMS The ES7 series are designed for the true RMS-to-DC conversion. ES7 accept low-level input signals from 0 to 400 mV RMS complex input waveforms. ES7 can be operated form either a single supply or dual supplies. The device draw less than 1 mA of quiescent supply current, furthermore, an enable pin is provided to turn-off the device, making it ideal for battery-powered applications.
- Averaging capacitor is typically 2.2uF
- Positive output voltage
- Computes RMS of AC and DC Signals
- Single or Dual Supply Operation
- Low Cost
- Power-Down Function
- Low Power: 600μA typically
- Wide power supply range : from ± 2.5V to ±10V Application * Digital Multi-Meters • 8-pin SOP package * Battery-Powered Instruments * Panel Meter
Pin Assignment: ES7 SOP 8 Pin Package Pin Description Pin No Symbol Type Description 1 RL - RL terminal. For zero-offset removing. 2 Vin I Measurement input. 3 PwrDown I Pull high (+Vs) to enable power-down function. 4 -Vs P Negative supply voltage.
5 Cav I/O Averaging capacitor
6 V out O Measurement output. 7 +Vs P Positive supply voltage.
8 COM P Power ground
I: input, O: output, P: power 4 5 ES7 RL Vin PwrDown -Vs Cav V out COM +Vs
Power Dissipation (Package) (TA= +25℃, Vs = +3V , -Vs = -3V , unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS Transfer Equation VOUT = avg.[(V IN) Averaging Time Constant 6 ms/μF CAV CONVERSION ACCURACY Total Error, Internal Trim (Notes 1) E S 7 ± 0 . 5 ± 1 . 0 mV ±% of Reading Total Error vs. Temperature (0 Reading/℃ Total Error vs. Supply ±0.1 ±0.01 mV ±% of Reading/V Total Error vs. DC Reversal VIN=+400mV ±2.0 ±% of Reading Crest Factor = 1 400mV Specified Accuracy 200mV 1.00 Crest Factor = 2 400mV 1.10 200mV 1.25 Crest Factor = 3 400mV 1.50 200mV 1.50 Additional Error (Note 2) Cav=2.2μF Crest Factor = 4 400mV 2.00 ±% of Reading FREQUENCY RESPONSE 35mV 50 100mV 200 200mV 200 Bandwidth for 1% Additional Error (0.09dB) 400mV 200 kHz 35mV 1.0 100mV 1.0 200mV 1.0 ±3dB Bandwidth 400mV 0.5 MHz
(TA= +25℃, Vs = +3V , -Vs = -3V , unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS INPUT CHARACTERISTICS Continuous RMS, All Supplies 0 to 400 mVRMS ±2.5V Supplies 1 ±3V Supplies 1.5 Input Signal range Peak Transient ±5V Supplies 2.8 VPK Input Resistance 6 8 10 MΩ Input Offset Voltage (Note3) ES7 ±0.5 mV OUTPUT CHARACTERISTICS +3V, -3V Supplies 1 Output Voltage Swing ±5V to ±10V Supplies 1 1.5 VRMS Output Resistance 8 10 12 kΩ Power SUPPLY Rated Performance ±3 V Dual Supplies ±2.5 ±10 V Single Supply +5 +20 V Supply Current ±3V Supply. Vin connects to COM 600 800 μA Supply Current (Power Down) Pin3 connects to V+ 60 75 μA Note 1: Accuracy is specified for 0 to 400mV, 1kHz sine-wave input. Accuracy is degraded at higher RMS signal levels. Note 2: Error vs. crest factor is specified as an additional error for 200mV RMS and 400mVRMS rectangular pulse input, pulse width = 200μs Note 3: The input offset voltage can be reduced or canceled by an external 500kohm variable resistor shown in Figure
Figure 1 shows the simplified sc hematic of ES7. It consists of four major sub-circuits: absolute value circuit (rectifier), square/divider, current mirror and buffer amplifier. The actual computation performed by the ES7 follows the equation: VRMS = Avg. [VIN2／VRMS] The input voltage, VIN, applied to the ES7 is conve rted to a unipolar current I 1 (Figure 1) by the absolute-value/voltage. This curren t drives one input of the squarer/divider that produces a current I4 , which has the transfer function: Ι Ι= Ι The current I4 drives the internal current mirror through a low-pass filter formed by R1 and the external capacitor, CAV. As long as the time constant of this filter is greater than the longest period of the input signal, I 4 is averaged. The current mirror returns a current, I3, to the square/divider to complete the circuit. The current I4 is then a function of the average of (I12/ I4), which is equal to I1RMS. The current mirror also produces a 2 ．I4 output current, IOUT, that can be used directly or converted to a voltage using resistor R2 and the internal buffer to provide a low-impedance voltage output. The transfer function for the ES7 is: VOUT = 2．R2．IRMS = VIN
The standard RMS connection requires onl y two external components, Rin and C av. in series with the input, as would typically be the case in single-supply operation. Figure 2. Standard connection for ES7.
- SW1 is opened for AC-coupled operation, or closed for direct input.
- PwrDown pin is pulled to –Vs or keeps floating for normal operation. Connect it to
+Vs will force ES7 to enter power down mode.
500kohm VR, 1kohm and 10ohm resi stors are used to redu ce zero offset voltage. pin1-RL and pin8-COM should not be too large. Figure 3. Adjust the zero-offset
- SW1 is opened for AC-coupled operation, or closed for direct input.
- PwrDown pin is pulled to –Vs or keeps floating for normal operation. Connect it to
+Vs will force ES7 to enter power down mode.
- The 500k ohm variable resistor can be used to adjust the zero-offset voltage.
- AC-coupled operation Refer to the standard circuit of ES7 s hown in Figure 2~3. ES7 will work in an AC-coupled operation when the SW1 is opened. In AC-coupled operation, an AC-coupled capacitor (Ccp) and bias resi stors Rin must be required. For a low frequency input under 100Hz, the Ccp need a 1uF or even larger ca pacitor to prevent input signal from decaying. Due to the architecture of ES7, a bias current is needed to activate the input buffer. The resistor Rin applied from Vin to GND supplie s a bias current flow path in AC-coupled operation. The bias current flows from GND to Vin through Rin will cause a bias voltage at Vin pin. So the Rin resistance shou ld not be too large (cause an additional zero offset) or too small (low input impedance). 2. Power Down Function The ES7 provides a power-down enable pin (Pin 3). To enable the device, this pin must be connected to –Vs or keep floating. If it is connected to V+, the device will enter power-down mode. 3. Post Filter CF To reduce the output ripple of ES7, a post filter capacitor C F is required. This capacitor should be connected as shown in figure 2. W ith post filter, the value of Cav should be just large enough to give the maximum dc error at the lowest frequency of interest. And the output ripple will be removed by the post filter.
Choosing the Averaging Time Constant The ES7 computes the RMS value of AC a nd DC signals. At low frequencies and DC, the output tracks the input exactly; at higher frequencies, the average output approaches the RMS value of the input signal. The act ual output differs from the ideal by an average (or DC) error plus some amount of ripple. The DC error term is a f unction of the value of C av and the input signal frequency. The output ripple is inversely proportional to the value of C av. Waveforms with high crest factors, such as a pulse train with low duty cycle, shoul d have an average time constant chosen to be at least ten times the signal period. Using a large value of C av to remove the output ripple increases the setting time for a step change in the input signal level. Figure 4 shows the relationship between Cav and 1 % settling time, where 110ms settling equals 4uF of C av. The settling time, or time for the RMS converter to settle to within a given percent of the change in RMS level, is set by the averaging time constant, which varies approximately 2:1 between decreasing and increasing input signals. In addition, the se ttling time also varies with input signal levels, increasing as the input signal is reduced, and decreasing as the input is increased. Frequency Response ES7 utilizes a logarithmic circuit in performing the RMS computation of the input signal. Table 1 represents the simplified frequenc y response of the converters from 35mV to 400mV for ES7. Caution must be used when designing RMS measuring systems so that overload does not occur. The input clipping level for ES7 is ±10V . Error R M S ±1% ±3db 35mV 50KHz 1MHz 100mV 200KHz 1MHz 200mV 200KHz 1MHz 400mV 200KHz 500KHZ T a b l e 1