CBC5300 datasheet(7/11 Pages) ETC2

7 / 11 page

EnerChip EH CBC5300

DS-72-06 Rev06

Page 7 of 11

Preliminary

As configured, the CBC5300 will operate with many transducer types. However, performance specifications

of transducers - namely output impedance - will affect the power conversion efficiency of the CBC5300 kit as

designed. Please contact Cymbet Applications Engineering at the phone number shown below to discuss your

specific application and desired transducer(s).

The CBC5300 module is designed to work with transducers having an output impedance over the range of 58Ω

to 4kΩ and an input voltage range of 270mV to 1.5V. The minimum open circuit voltage to start operation is

700mV. Peak efficiency will occur at a nominal transducer input voltage of 800mV to 1.0V at 1kΩ. Operating

characteristics for most transducer types are typically available from the manufacturer’s data sheet. An

example photovoltaic cell operating curve is shown below. Output impedance, operating voltage, and peak

power point can also be verified by empirical measurements. To do this, measure the load voltage and current

as a variable load impedance across the transducer is swept over a broad enough range where the peak power

point can be found by finding the maximum product of the measured load voltage and current.

To configure the CBC5300 to work with a given transducer, the optimal transducer operating voltage point

must first be obtained though the manufacturer’s data sheet or from empirical measurements. Next calculate

the values needed for a voltage divider to set the operating voltage point on the VOPER pin (pin 10). The top

of the voltage divider shown in Figure 3 uses VREG (pin 11) as its voltage source; the bottom of the voltage

divider is connected to ground. VOPER is equal to VREG * (R2 / (R1 + R2)), where VREG is nominally 4.06V and

R2 (bottom resistor) is in the range of 500kΩ to 1MΩ with the optimal value around 750kΩ. Note: Better

circuit performance (i.e., less input ripple voltage) will be obtained if R2 is made smaller than 750kΩ. A more

useful formula is: R1 = R2 * ((VREG / VOPER) - 1). Example: For a 1kΩ photovoltaic cell with operating voltage of

1.01V, R1 can be determined as R1 = 1MΩ * ((4.06V / 1.01V) - 1) = 3.02MΩ. A 3.01MΩ resistor is the nearest

standard value. R2 was chosen as a standard resistor value. 750kΩ for R2 is also a standard resistor value but

the VOPER voltage will be further away from nominal due to the standard resistor values available for R1.

Capacitor C1 (47µF) is used to set the bandwidth of the boost converter control loop. If a low impedance

transducer is used the value of C1 might have to be reduced in value. This can be verified using an oscilloscope

to check the waveform on GATE (pin 3). The waveform should be three pulses followed by a longer interval,

followed again by three pulses. The three pulses will have approximately 16.7µs of high duration followed by

16.7µs of low duration. If more than three pulses are in the waveform then the value of C1 should be reduced

to obtain the nominal waveform.

Setting the Under Voltage Lockout Voltage

The under voltage lockout (UVLO SEL) voltage should be set at or above the operating point, VOPER, in order to

prevent the EnerChip from inadvertently powering the boost converter when insufficient input transducer power

is available. Normally, UVLO should be set to a value that is 20% to 80% above VOPER. UVLO SEL can be set by

adding one or more series diodes between UVLO SEL and VIN. For example, the nominal voltage at UVLO SEL is

700mV; to raise it to 1.4V, insert one standard silicon diode. To reach intermediate voltages, Schottky diodes

may be used.

VOC: Open-circuit voltage

ISC: Short-circuit current

VOP: Optimum operating voltage

IOP: Optimum operating current

PMAX: Maximum operating power

Current-Voltage Curve

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