Datasheet LTC6103 (Analog Devices) - 9

LTC6103
APPLICATIONS INFORMATION
CMPZ4697 10k VLOGIC (3.3V TO 5V) M1 Si4465 7 3 LTC1540 RSENSE(LO) R + I SENSE(HI) LOAD 100mΩ 10mΩ 4 8 V Q1 – OUT VIN 5 CMPT5551 40.2k 6 4.7k 301Ω 301Ω 8 7 6 5 1.74M HIGH 2 1 RANGE INDICATOR LTC6103 619k (ILOAD > 1.2A) HIGH CURRENT 1 2 4 RANGE OUT BAT54C 250mV/A 7.5k VLOGIC LOW CURRENT RANGE OUT 6103 F03b R5 250mV/A (VLOGIC + 5V) ≤ VIN ≤ 60V 7.5k 0A ≤ ILOAD ≤ 10A
Figure 3b. The LTC6103 Allows High-Low Current Ranging
Care should be taken when designing the printed circuit In addition, the output impedance is determined by ROUT. If board layout to minimize input trace resistance (to Pins 5, the circuit to be driven has high enough input impedance, 6, 7 and 8), especially for small RIN values. Trace resistance then almost any useful output impedance will be accept- to the –IN terminals will increase the effective RIN value, able. However, if the driven circuit has relatively low input causing a gain error. Trace resistance on +IN terminals will impedance or draws spikes of current, as an ADC might have an effect on offset error. These errors are described do, then a lower ROUT value may be required in order to in more detail later in this data sheet. In addition, internal preserve the accuracy of the output. As an example, if the device resistance will add approximately 0.3Ω to RIN. input impedance of the driven circuit is 100 times ROUT, then the accuracy of VOUT will be reduced by 1% since:
Selection of External Output Resistor, ROUT
R • R OUT IN DRIV ( EN) The output resistor, ROUT, determines how the output cur- V = I OUT OUT • R + R rent is converted to voltage. V OUT IN DRIV ( EN) OUT is simply IOUT • ROUT. In choosing an output resistor, the maximum output voltage 100 must fi rst be considered. If the circuit following is a buf- = I • R • = . 0 99 • I • R OUT OUT OUT OUT fer or ADC with limited input range, then R 101 OUT must be chosen so that IOUT(MAX) • ROUT is less than the allowed maximum input range of this circuit. 6103f 9