LT1510/LT1511/LT1512 Battery charger IC

Question

1. Can we create a PV based battery charger using LT1510/LT1511/LT1513? The input voltage will be connected to a PV panel of appropriate spec. Is there any additional thing to be taken cared of? 
 LT1510 is a current mode PWM step- down switcher where the internal switch is capable of handling 1.5A current. 2. If we need higher current capability is there any way to interface an external switch? 
 The switch inside IC is an NPN transistor although the switching frequency is 500kHz. We studied usually for high switching frequencies we prefer MOSFET, 3 . Is there any reason for using BJT for 500kHz switching?

ADIApproved · Accepted Answer

Typically, a switchmode converter will attempt to draw enough current from its source to maintain regulation at the output. A PV voltage source intrinsically has a high series resistance. This is a bad combination. As the converter tries to extract more current from the source the source voltage drops, and little or no power is drawn from the source. Ideally, a converter would operate at the input current/voltage point which delivers maximum power to the converter. See the discussion at https://en.wikipedia.org/wiki/Maximum_power_point_tracking . 
 The LTC4121 uses a simplified, effective MPPT technique. The LTC4121 battery-charging current is limited to 400mA, The LT8490 and LTC4015 include full-featured MPPT control using an input voltage/current sweep to identify the maximum power point. 
 The LT1510 is not designed to support higher current capability with an external switch. 
 The LT1510 was developed well before I worked here. I do not know why a BJT is used as the power switch. It may be that at the earlier development date processes supporting power FETs were not widely used.)

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LT1510/LT1511/LT1512 Battery charger IC