QW1 TechTools, QW1 Datasheet - Page 4

• Manufacturer Part Number: QW1
• Description: PROGRAMMER PIC MCU QUICKWRITER
• Manufacturer: TechTools
• Series: QuickWriter™r
• Type: QuickWriterr

Specifications of QW1

• Contents: MCU Programmer with In-Circuit Serial Programming Cable and Optional GANG Adapters
• For Use With/related Products: PIC Micro® MCU
• For Use With: CBL-ICSP - CABLE PROG QUICKWRITER SERIALQW-4SSOP18 - ADAPTER QUICKWRITER 4GANG 18SSOPQW-4SSOP28 - ADAPTER QUICKWRITER 4GANG 28SSOPQW-4SO8/14W - ADAPT QUICKWRTR 4GANG 8/14SOIC WQW-4SO8/14N - ADAPT QUICKWRTR 4GANG 8/14SOIC NQW-4SOIC18 - ADAPTER QUICKWRITER 4GANG 18SOICQW-4ZIF18 - ADAPTER QUICKWRITER 4-GANG 18ZIFQW-4SOIC28 - ADAPTER QUICKWRITER 4GANG 28SOICQW-4PLCC44 - ADAPTER QUICKWRITER 4GANG 44PLCCQW-4ZIF40/28 - ADAPT QUICKWRITER 4GANG 40/28ZIFMP-ZIF14 - ADAPTER QUICKWRITER 14-PIN ZIFMP-SOIC8/14 - ADAPTER QUICKWRITER 8/14-SOICMP-SSOP18 - ADAPTER QUICKWRITER 18-SSOPMP-SSOP28 - ADAPTER QUICKWRITER 28-SSOPMP-14000 - ADAPTR QUICKWRTR PIC14000 28-PINMP-SOIC18 - ADAPTER QUICKWRITER 18-SOICMP-SOIC28 - ADAPTER QUICKWRITER 28-SOICMP-PLCC44 - ADAPTER QUICKWRITER 44-PIN PLCCMP-ZIF18/28 - ADAPTER QUICKWRITER 18/28PIN ZIFMP-ZIF40 - ADAPTER QUICKWRITER 40-PIN ZIF

VCC (2)
Who powers the target?
It is possible to do in-circuit programming with the programmer powering the target or with the target
powering itself. There are trade-offs and limitations with each choice.
Programmer Powered
The programmer can provide up to 100ma of power to power up your target during programming. This
gives it complete control over programming. However, there are a few things to watch for.
Back-feeding Regulators
Most power regulators regulate by adjusting how much current they DRIVE into the circuit. Few are
capable of sinking current. They depend on the load itself to sink current. Since they are not designed to
sink current, many regulators can be damaged if their OUTPUT becomes higher than their INPUT pin.
This is exactly what happens if you allow the programmer to power the target and do not power the input to
the regulator. Most 3-terminal regulator design guides specify if the regulator is tolerant of this condition
or how to design to make it tolerant.
Brown-outs
It is possible that the programmer can provide enough current to power up the target until actual
programming begins. At that time, the additional power required for programming could cause the entire
target board voltage to drop and the programming to fail. Alternatively, the average voltage could stay
valid, but noise could appear on VCC in response to surge current requirements by the circuit of device
being programmed. Either symptom would be an indication that the board requires more than the 100ma of
current the programmer is capable of supplying.
Partially powered targets
If you allow the programmer to back-feed the VCC power rail on the target, that would power up VCC, but
may leave other power rails on the target un-powered. This could be damaging to some components.
For example, if you have a 12 volt power supply powering some devices and this is normally regulated
down to 5V for the PICmico MCU and others, then the 12V devices would not get powered when the
programmer drives current into the VCC (5V) rail. This could cause 5V to be driven into some un-powered
devices.
Similar problems can occur even in 5V only systems if they have multiple isolated power rails.
Capacitance
QuickWriter can drive up to 1000uF on the VCC rail. If there is more capacitance than this,
QuickWriter will report that VCC failed to rise fast enough and will abort programming.
The larger the VCC capacitance, the longer it takes for them to bleed down after programming is
complete, depending on the target load. Large capacitance could increase programming times. If
this becomes a problem, you can add a bleed resister between VCC and GROUND on the ICSP
cable to speed up the bleed-down. Keep the VCC load under 100ma (target + bleed resister.)