L5987TR STMicroelectronics, L5987TR Datasheet - Page 12

• Manufacturer Part Number: L5987TR
• Description: IC REG SW 3A STEPDOWN 8-VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5987TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 18 V
• Current - Output: 3A
• Frequency - Switching: 250kHz
• Voltage - Input: 2.9 ~ 18 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 8-VFQFN, 8-VFQFPN
• Power - Output: 1.5W
• Output Voltage: 0.6 V
• Output Current: 3 A
• Output Power: 1.5 W
• Input Voltage: 2.9 V to 18 V
• Switching Frequency: 250 KHz
• Mounting Style: SMD/SMT
• Duty Cycle (max): 100 %
• For Use With: 497-8369 - BOARD EVALUATION FOR L5987
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-8494-2

Functional description
5.3
12/41
Error amplifier and compensation
The error amplifier (E/A) provides the error signal to be compared with the sawtooth to
perform the pulse width modulation. Its non-inverting input is internally connected to a 0.6 V
voltage reference, while its inverting input (FB) and output (COMP) are externally available
for feedback and frequency compensation. In this device the error amplifier is a voltage
mode operational amplifier so with high DC gain and low output impedance.
The uncompensated error amplifier characteristics are the following:
Table 5.
In continuos conduction mode (CCM), the transfer function of the power section has two
poles due to the LC filter and one zero due to the ESR of the output capacitor. Different
kinds of compensation networks can be used depending on the ESR value of the output
capacitor. In case the zero introduced by the output capacitor helps to compensate the
double pole of the LC filter a type II compensation network can be used. Otherwise, a type
III compensation network has to be used (see
compensation network selection).
Anyway the methodology to compensate the loop is to introduce zeros to obtain a safe
phase margin.
Maximum source/sink current
Uncompensated error amplifier characteristics
Output voltage swing
Low frequency gain
Parameter
Slew rate
GBWP
Doc ID 14972 Rev 3
Chapter 6.4
for details about the
25 mA/40 mA
0 to 3.3 V
4.5 MHz
100 dB
7 V/μs
Value
L5987