Datasheet

VBG
1.229V
CTRL
Error
Amplifier
FB
TPS61170
www.ti.com SLVS789C – NOVEMBER 2007– REVISED APRIL 2011
For optimum performance, use the PWM mode in the range of 5kHz to 100kHz. The requirement of minimum
frequency comes from the EasyScale detection delay and detection time specification for the mode selection.
The device can mistakenly enter 1 wire mode if the PWM signal frequency is less than 5kHz. Because there is
an internal fixed ON-time error of 40nS, the FB voltage absolute value will be different than expected when the
PWM frequency is above 100kHz. For example, the additional duty cycle of 3.2% due to the ON-time error
increases the FB voltage when using an 800kHz PWM signal. A compromise between PWM frequency and FB
voltage accuracy extends the frequency range. Adding an external RC filter to the pin serves no purpose.
Figure 14. Block Diagram of Programmable FB Voltage Using PWM Signal
1 WIRE PROGRAM MODE
The CTRL pin features a simple digital interface to control the feedback reference voltage. The 1 wire mode can
save the processor power and battery life as it does not require a PWM signal all the time, and the processor can
enter idle mode if available.
The TPS61170 adopts the EasyScale™ protocol, which can program the FB voltage to any of the 32 steps with
single command. See Table 1 for the FB pin voltage steps. The programmed reference voltage is stored in an
internal register. The default value is full scale when the device is first enabled (V
FB
= 1.229V). A power reset
clears the register value and reset it to default.
EasyScale™
EasyScale is a simple but very flexible one pin interface to configure the FB voltage. The interface is based on a
master-slave structure, where the master is typically a microcontroller or application processor. Figure 15 and
Table 1 give an overview of the protocol. The protocol consists of a device specific address byte and a data byte.
The device specific address byte is fixed to 72 hex. The data byte consists of five bits for information, two
address bits, and the RFA bit. The RFA bit set to high indicates the Request for Acknowledge condition. The
Acknowledge condition is only applied if the protocol was received correctly. The advantage of EasyScale
compared with other on pin interfaces is that its bit detection is in a large extent independent from the bit
transmission rate. It can automatically detect bit rates between 1.7kBit/sec and up to 160kBit/sec.
Table 1. Selectable FB Voltage
FB voltage
D4 D3 D2 D1 D0
(mV)
0 0.000 0 0 0 0 0
1 0.031 0 0 0 0 1
2 0.049 0 0 0 1 0
3 0.068 0 0 0 1 1
4 0.086 0 0 1 0 0
5 0.104 0 0 1 0 1
6 0.123 0 0 1 1 0
7 0.141 0 0 1 1 1
8 0.160 0 1 0 0 0
9 0.178 0 1 0 0 1
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